Impairment of bone turnover in elderly women with hip fracture

Bone metabolism subgroups identified as hip fracture patients via clustering

PURPOSE

The aim of the study was to describe the bone metabolism status that underlies a hip fracture.

METHODS

Estimated glomerular filtration rate (e-GFR), calcium (Ca), phosphorus (P), total (ALP) and bone specific alkaline phosphatase (b-ALP), intact parathyroid hormone (i-PTH), 25-hydroxy-vitamin D (25OHD), total procollagen type I amino-terminal propeptide (PINP), and N-terminal peptide of collagen I (NTx), measured at admission in 272 hip fracture patients, were ex post analyzed by K-means clustering and principal component analysis and were evaluated by a clinician.

RESULTS

Four components, mainly consisting of b-ALP, PINP, ALP, and NTx; e-GFR and P; i-PTH and 25OHD; and Ca explained about 70% of the variability. A total of 184 patients clustered around a centroid (A) with low 25OHD (13.2 ng/ml), well-preserved kidney function (e-GFR=67.19 ml/min/1.73m²), normal Ca, P, i-PTH and bone markers, with the exception of slightly increased NTx (24.82nMBCE). Cluster B (n=70) had increased i-PTH (93.38 pg/ml), moderately decreased e-GFR, very low 25OHD (8.68 ng/dl), and high bone turnover (b-ALP 28.46 U/L, PINP 69.87 ng/ml, NTx 31.3nMBCE). Cluster C (n=17) also had hyperparathyroidism (80.35 pg/ml) and hypovitaminosis D (9.15 ng/ml), low e-GFR(48.89 ml/min/1.73m²), and notably high ALP (173 U/L) and bone markers (b-ALP 44.64 U/L, PINP 186.98 ng/ml, NTx 38.28nMBCE). According to the clinician, 62 cases clearly had secondary hyperparathyroidism.

CONCLUSIONS

Based on serum measurements, the dominant patterns of bone metabolism were normal bone turnover with high normal NTx, and secondary hyperparathyroidism related to chronic kidney disease and hypovitaminosis D. The bone formation markers, e-GFR, NTx, and P composed the most important factors.

Bone Turnover Markers Are Not Associated With Hip Fracture Risk: A Case-Control Study in the Women's Health Initiative

Current guidelines recommend that serum C-terminal telopeptide of type I collagen (CTX) and serum procollagen type 1 aminoterminal propeptide (PINP), measured by standardized assays, be used as reference markers in observational and interventional studies. However, there are limited data to determine whether serum CTX and PINP are associated with hip fracture risk among postmenopausal women. We determined the associations of serum CTX and serum PINP with hip fracture risk among postmenopausal women aged 50 to 79 years at baseline. We performed a prospective case-control study (400 cases, 400 controls) nested in the Women's Health Initiative Observational Study, which enrolled participants at 40 US clinical centers. Cases were women with incident hip fracture not taking osteoporosis medication; hip fractures were confirmed using medical records. Untreated controls were matched by age, race/ethnicity, and date of blood sampling. Serum CTX and serum PINP were analyzed on 12-hour fasting blood samples. The main outcome measure was incident hip fracture risk (mean follow-up 7.13 years). After adjustment for body mass index, smoking, frequency of falls, history of fracture, calcium and vitamin D intake, and other relevant covariates, neither serum CTX level nor serum PINP level was statistically significantly associated with hip fracture risk (CTX p_trend  = 0.22, PINP p_trend  = 0.53). Our results do not support the utility of serum CTX level or PINP level to predict hip fracture risk in women in this age group. These results will inform future guidelines regarding the potential utility of these markers in fracture prediction. © 2018 American Society for Bone and Mineral Research.

Biochemical Markers of Bone Turnover and Fracture Prediction

Low bone mineral density is a strong risk factor for fractures in the older woman. Biochemical markers of bone turnover may predict fracture risk independently of bone mineral density. High levels of bone resorption markers are associated with increased risk of fracture in both retrospective and prospective studies, although the evidence for bone formation markers and fracture risk is equivocal. For example, the risk of fracture is increased up to two-fold in women with elevated levels of several markers of bone resorption. Prediction models have been developed to predict the 10–year risk of fracture using bone mineral density and biochemical markers of bone turnover and these could prove very useful in clinical practice.

CER1 gene variations associated with bone mineral density, bone markers, and early menopause in postmenopausal women

Background

Osteoporosis has a multifactorial pathogenesis characterized by a combination of low bone mass and increased fragility. In our study, we focused on the effects of polymorphisms in CER1 and DKK1 genes, recently reported as important susceptibility genes for osteoporosis, on bone mineral density (BMD) and bone markers in osteoporotic women. Our objective was to evaluate the effect of CER1 and DKK1 variations in 607 postmenopausal women. The entire DKK1 gene sequence and five selected CER1 SNPs were amplified and resequenced to assess whether there is a correlation between these genes and BMD, early menopause, and bone turnover markers in osteoporotic patients.

Results

Osteoporotic women seem to suffer menopause 2 years earlier than the control group. The entire DKK1 gene sequence analysis revealed six variations. There was no correlation between the six DKK1 variations and osteoporosis, in contrast to the five common CER1 variations that were significantly associated with BMD. Additionally, osteoporotic patients with rs3747532 and rs7022304 CER1 variations had significantly higher serum levels of parathyroid hormone and calcitonin and lower serum levels of osteocalcin and IGF-1.

Conclusions

No significant association between the studied DKK1 variations and osteoporosis was found, while CER1 variations seem to play a significant role in the determination of osteoporosis and a potential predictive role, combined with bone markers, in postmenopausal osteoporotic women.

Clinical application of biochemical markers of bone turnover

With the ageing population in most countries, disorders of bone and mineral metabolism are becoming increasingly relevant to every day clinical practice. Consequently, the interest in, and the need for effective measures to be used in the screening, diagnosis and follow-up of such pathologies have markedly grown. Together with clinical and imaging techniques, biochemical tests play an important role in the assessment and differential diagnosis of metabolic bone disease. In recent years, the isolation and characterisation of cellular and extracellular components of the skeletal matrix have resulted in the development of molecular markers that are considered to reflect either bone formation or bone resorption. These biochemical indices are non-invasive, comparatively inexpensive and, when applied and interpreted correctly, helpful tools in the diagnostic and therapeutic assessment of metabolic bone disease. This review provides an overview of the current evidence regarding the clinical use of biochemical markers of bone remodelling in bone disease, with an emphasis on osteoporosis.

Effect of fracture on bone turnover markers: a longitudinal study comparing marker levels before and after injury in 113 elderly women

In this longitudinal, prospective, and population-based study (n = 1044), seven BTMs were assessed before and after trauma in 113 elderly women (85 with fractures). Markers were not altered in the immediate postfracture period but were clearly elevated during fracture repair. Recent fracture should thus be taken into account when markers are used in clinical practice.

INTRODUCTION

Fracture may influence the levels of bone turnover markers (BTM) and have implications for their use in clinical practice. In this longitudinal, prospective, and population-based study, we assessed prefracture levels of BTMs and compared them with postfracture levels of the same individuals immediately after fracture and during fracture repair. This is the first study in which the effect of fracture on bone markers has been evaluated with prefracture samples available.

MATERIALS AND METHODS

Serum and urine were collected at the emergency unit from 85 women (77.9 +/- 1.8 yr) who sustained a fracture after low-energy trauma and 28 controls (77.8 +/- 2.0 yr) with similar trauma but no fracture. All were participants of the Malmö OPRA study (n = 1044), and pretrauma samples were collected 1.05 +/- 0.85 yr before. Bone turnover was assessed by seven different BTMs reflecting different stages of bone metabolism {C-terminal cross-linked telopeptides of type I collagen [S-CTX], S-TRACP5b, N-terminal propeptides of type I collagen [S-PINP], serum osteocalcin (S-OC[1-49] and S-TotalOC), urinary deoxypyridinoline [U-DPD], and urinary osteocalcin [U-OC]}.

RESULTS

BTMs sampled within a few hours after fracture were not altered from preinjury levels. Both bone formation and bone resorption markers were, however, significantly increased 4 mo after fracture. The elevation was most pronounced after hip fracture. Bone turnover remained elevated up to 12 mo after fracture.

CONCLUSIONS

We believe this study extends our knowledge on the skeletal postfracture metabolic processes. In addition, it may provide a basis for future means to monitor pharmacological intervention promoting fracture healing.

Prediction and discrimination of osteoporotic hip fracture in postmenopausal women

Osteoporotic hip fractures increase dramatically with age and are responsible for considerable morbidity and mortality. Several treatments to prevent the occurrence of hip fracture have been validated in large randomized trials and the current challenge is to improve the identification of individuals at high risk of fracture who would benefit from therapeutic or preventive intervention. We have performed an exhaustive literature review on hip fracture predictors, focusing primarily on clinical risk factors, dual X-ray absorptiometry (DXA), quantitative ultrasound, and bone markers. This review is based on original articles and meta-analyses. We have selected studies that aim both to predict the risk of hip fracture and to discriminate individuals with or without fracture. We have included only postmenopausal women in our review. For studies involving both men and women, only results concerning women have been considered. Regarding clinical factors, only prospective studies have been taken into account. Predictive factors have been used as stand-alone tools to predict hip fracture or sequentially through successive selection processes or by combination into risk scores. There is still much debate as to whether or not the combination of these various parameters, as risk scores or as sequential or concurrent combinations, could help to better predict hip fracture. There are conflicting results on whether or not such combinations provide improvement over each method alone. Sequential combination of bone mineral density and ultrasound parameters might be cost-effective compared with DXA alone, because of fewer bone mineral density measurements. However, use of multiple techniques may increase costs. One problem that precludes comparison of most published studies is that they use either relative risk, or absolute risk, or sensitivity and specificity. The absolute risk of individuals given their risk factors and bone assessment results would be a more appropriate model for decision-making than relative risk. Currently, a group appointed by the World Health Organization and lead by Professor John Kanis is working on such a model. It will therefore be possible to further assess the best choice of threshold to optimize the number of women needed to screen for each country and each treatment.

The Importance of Parathyroid Hormone and Vitamin D Status in the Treatment of Osteoporosis and Renal Insufficiency

Suboptimal vitamin D status is common in sick, elderly patients and is associated with secondary hyperparathyroidism, increased bone turnover, and accelerated bone loss. Nutritional supplementation of elderly patients with vitamin D and calcium has been associated with a reduction in fractures and falls. Recently, the National Kidney Foundation (NKF) recommended screening parathyroid hormone (PTH) levels in those with glomerular filtration rates (GFR) less than 60 mL/min. The PTH target range increases as renal failure progresses because of skeletal resistance. When PTH levels are above the target range, measurement of serum 25-hydroxyvitamin D (25-OH-D) is recommended. If the 25-OH-D level is less than 30 ng/mL, supplementation with vitamin D is recommended. Practitioners should consider supplementing most residents with vitamin D and calcium or follow NKF guidelines.

Women with hip fracture have a greater rate of decline in bone mineral density than expected: another significant consequence of a common geriatric problem

INTRODUCTION

Hip fracture is a major public health problem, annually affecting over 350,000 persons in the United States and 1.6 million worldwide. Consequences include decreased survival, loss of independence, and increased risk of subsequent fractures. A substantial decline in bone mineral density (BMD) also occurs, yet the magnitude of the decline specifically attributable to hip fracture has not been documented.

METHODS

To determine the amount of BMD decline attributable to hip fracture, the rate of decline in BMD in a cohort of hip fracture patients was compared with that in a cohort of women of similar age and BMD but without hip fracture. All subjects were community dwelling when enrolled. Hip fracture patients in the Baltimore Hip Studies (BHS) came from two hospitals in Baltimore, Maryland, from 1992 through 1995; comparison subjects came from the Study of Osteoporotic Fracture (SOF) enrolled in four areas of the United States during the same period. Eighty-four white, female hip fracture patients 65 years and older from the BHS were compared with 168 SOF participants matched on age, race, and BMD at baseline. BMD of the femoral neck and total hip was measured by dual-energy x-ray absorptiometry.

RESULTS

Hip fracture patients had a greater decline in BMD during the 12-month postfracture follow-up than that expected on the basis of the nonfracture cohort: 4.9% vs. 0.4% at the femoral neck and 3.5% vs. 0.7% for the total hip. The decline in BMD in hip fracture patients was 11.8 times the amount expected at the femoral neck (matched on age and baseline BMD and adjusted for between-cohort differences in smoking prevalence) and 4.9 times that expected for the total hip at the end of 1 year after the hip fracture.

CONCLUSION

In this sample of older women, bone loss over the year following hip fracture far exceeded that expected and is an important clinical management concern.

Biochemical bone markers are useful to monitor fracture repair

Biochemical bone markers reflect bone metabolism but little is known regarding their usefulness during fracture repair. Reduced bone mineral density may influence fracture healing. We hypothesized that low bone mineral density results in decreased levels of bone markers during the acute phase of fracture healing, especially in women who are postmenopausal. We also addressed the question of different fracture types and locations resulting in different levels of bone markers. Urinary levels of N-terminal cross-linked telopeptide, deoxypyridinoline, and pyridinoline were measured preoperatively and postoperatively in patients with hip fractures, distal forearm fractures, and in 25 control subjects. Bone mineral density was determined using quantitative computed tomography of the spine. Patients with low bone mineral density, especially women who were postmenopausal, had greater concentrations of N-terminal cross-linked telopeptide when compared with patients with normal bone mineral density or men. Patients with pertrochanteric fractures had greater concentrations than patients with femoral neck fractures, as did patients with hip fractures compared with patients with fractures of the distal forearm. These results suggest that levels of bone markers increase during fracture healing despite low bone mineral density and that different fracture types and locations result in different levels of bone markers.

LEVEL OF EVIDENCE

Prognostic study, Level I (high quality prospective study-all patients were enrolled at the same time with > or = 80% of followup of enrolled patients). See the Guidelines for Authors for a complete description of levels of evidence.

Serum concentrations of cross-linked N-telopeptides of type I collagen: new marker for bone resorption in hemodialysis patients

BACKGROUND

Urinary cross-linked N-telopeptide of type I collagen (NTX) is a reliable bone resorption marker in patients with metabolic bone disease. We assessed a clinically available serum NTX assay suitable for anuric patients on hemodialysis (HD).

METHODS

Serum concentrations of NTX, C-terminal telopeptide of type I collagen (beta-CTX), pyridinoline (PYD), and deoxypyridinoline (DPD) were determined as bone resorption markers, and those of bone alkaline phosphatase (BAP) and intact osteocalcin (OC) as bone formation markers, in 113 male HD patients (mean age, 59.3 years; mean HD duration, 67.7 months). Each patient's bone mineral density (BMD) in the distal third of the radius was measured twice, with a 2-year interval between measurements, by dual-energy x-ray absorptiometry.

RESULTS

Serum NTX correlated significantly with beta-CTX, PYD, DPD, BAP, and intact OC. NTX, as well as beta-CTX, PYD, DPD, BAP, and intact OC, correlated significantly with BMD at the time of measurement. NTX, beta-CTX, and DPD correlated significantly with the annual change in BMD during the 2-year period thereafter, in contrast to PYD, BAP, and intact OC. Patients in the highest quartile of serum NTX concentrations showed the fastest rate of bone loss. The sensitivity and specificity for detecting rapid bone loss were 48% and 83%, respectively, for serum NTX.

CONCLUSION

Serum NTX may provide a clinically relevant serum assay to estimate bone turnover in HD patients.

Vitamin D status and bone turnover in women with acute hip fracture

Hypovitaminosis D is common in elderly women. Few data are available on vitamin D status and bone turnover in women with acute hip fracture. The aims of this study were to determine whether elderly Italian women with an acute hip fracture also had low vitamin D levels and an increase of bone turnover compared with elderly women with osteoporosis but without fractures. Seventy-four women with acute osteoporotic hip fracture and 73 women with postmenopausal osteoporosis were studied. All women were self-sufficient and had adequate sunlight exposure. To exclude the effect of trauma on serum 25-hydroxycolecalciferol levels and bone markers (bone alkaline phosphatase and C-terminal telopeptides of Type I collagen as indices of bone formation and bone resorption), blood samples were drawn within 24 hours of the fracture. Current data indicated that in our patients the prevalence of hypovitaminosis D is common although to a lesser extent than in women who are housebound. Women with acute hip fractures had a higher prevalence of vitamin deficiency defined as serum 25-hydroxycolecalciferol lower than 12 ng/mL, compared with women with osteoporosis. Moreover, the presence of fracture did not influence the rate of bone formation, whereas the increase in bone resorption could be attributed to an older age of women with acute hip fracture because of similar values of parathyroid hormone levels in the two groups.

Beneficial Effect of Etidronate Therapy in Immobilized Hip Fracture Patients[Retracted]

OBJECTIVES

Hip fracture is among the most common causes of acute immobilization in elderly patients leading to increased bone resorption, and elderly patients with hip fracture are at high risk for a subsequent hip fracture.

DESIGN

In this double-blind, randomized, prospective study, 80 female patients who were immobilized because of a hip fracture were divided into two groups. The etidronate group received oral administration of 200 mg/day etidronate for 2 wks starting 1 day after the surgery. Then, after a 9-wk intermission, etidronate administration was resumed for 2 wks. The placebo group received placebo in a similar manner.

RESULTS

At baseline, both groups had high serum concentrations of ionized calcium, high urinary deoxypyridinoline (D-Pyr) concentrations, and decreased calcitriol concentrations, suggesting immobilization-induced hypercalcemia and inhibition of renal synthesis of calcitriol. After treatment, serum calcitriol concentrations increased in the etidronate and placebo groups. The etidronate group had significant decreases in serum ionized calcium and urinary D-Pyr, and the placebo group had higher serum calcium and urinary D-Pyr concentrations.

CONCLUSIONS

Etidronate therapy inhibits bone resorption and improves calcium balance, and such therapy may prevent bone loss and reduce the risk of subsequent hip fracture.

Bone remodeling markers: assessment of fracture risk and fracture risk reduction

There is an increasing repertoire of laboratory tests available for assessing the bone remodeling process. Biochemical markers of bone remodeling can be measured in serum or urine, and have a number of potential roles in the management of fracture risk. Differences in remodeling between individuals might be related to fracture risk and could be used to target therapy. Change in remodeling with therapy could be related to fracture risk reduction and the choice of therapy could be influenced by knowledge of bone remodeling. Biochemical therapeutic monitoring may improve patient understanding and therapeutic adherence. The rate of bone remodeling is weakly predictive of fracture risk in individuals who are not receiving therapy; however, it is not clear whether this is independent of other risk factors. There is increasing evidence that change in bone mineral density does not explain fracture risk reduction with antiresorptive therapies, and that therapeutic benefit might be explained by change in bone turnover. Additional studies and information are required to allow these scientific advances to be translated into cost-effective and validated clinical protocols. Optimizing the precision and accuracy of bone turnover assessment remains an important priority.

Preventing fractures in elderly people

Preventing fractures in elderly people is a priority, especially as it has been predicted that in 20 years almost a quarter of people in Europe will be aged over 65. This article describes the factors contributing to fracture, interventions to prevent fracture, and the various treatments.

Biochemical markers of bone remodeling

Because of the aging population in most countries, disorders of bone and mineral metabolism are becoming increasingly relevant to everyday clinical practice. Consequently, the interest in, and the need for effective measures to be used in the screening, diagnosis, and follow-up of such pathologies has markedly grown. Together with clinical and imaging techniques, laboratory tests play an important role in the assessment and differential diagnosis of metabolic bone disease.

Comparison of biochemical markers of bone turnover and bone mineral density between hip fracture and vertebral fracture

Bone density and the biochemical markers of bone turnover were compared between 26 hip-fracture patients and 41 vertebral-fracture patients after age adjustment to investigate whether or not type of osteoporosis differs between hip fracture and vertebral fracture. C-Terminal propepides of type I collagen (PIPC) was lower in hip fracture than vertebral fracture. The other bone formation markers (bone-specific alkaline phosphatase [ALP], osteocalcin) tended to be lower, and bone resorption markers (deoxypyridinoline, C-telopeptide crosslinking of type I collagen [CTX] tended to be higher in hip fracture compared to vertebral fracture. Mean of Z-scores of spine bone mineral density (BMD) in hip fracture and vertebral fracture were -0.461 and -0.919, respectively. Mean of Z-scores of femoral neck BMD in hip fracture and vertebral fracture were -0.994 and -0.361, respectively. All Z-scores were negative values, which means reduction of BMD compared to decade-matched controls. Z-scores of bone formation markers, such as bone-specific ALP, osteocalcin, and PIPC, were positive values in vertebral fracture, which means an increase against decade-matched controls, whereas those were negative values in hip fracture. Z-scores of bone resorption markers, such as deoxypyridinoline and CTX, were greater in hip fracture than in vertebral fracture. To express bone balance between formation and resorption in hip fracture and vertebral fracture, we calculated an uncoupling status index (USI) by the values of biochemical markers. USI of hip fracture showed a great negative value (-1.29), which indicates excess of bone resorption over formation, whereas that of vertebral fracture showed a small positive value (0.23). In conclusion, bone formation markers increase in vertebral fractures, but decrease in hip fracture. Bone resorption markers increase in both fracture, but greater increase in hip fracture.

Diurnal, week-to-week, and long-term variation in urine deoxypyridinoline cross-link excretion in healthy older women

OBJECTIVES

To establish a reference range for morning and afternoon excretion of urinary deoxypyridinoline (DPD) in apparently healthy older women selected from a volunteer database. To assess the extent of diurnal variation and short and long-term within-subject longitudinal variation.

DESIGN

Prospective, observational, cohort study.

SETTING

Clinical Age Research Unit, King's College School of Medicine, London, United Kingdom.

PARTICIPANTS

Forty-two women aged 68 to 89 (median age 75) selected from a volunteer database.

METHODS

Subjects completed an osteoporosis risk factor questionnaire and a physical examination and had a measurement of the broadband ultrasound attenuation and speed of sound of their right heel. Subjects provided six urine samples: morning and afternoon at baseline and 1 week and 60 weeks later for measurement of DPD.

RESULTS

The mean baseline values for DPD of morning and afternoon samples were 7.2 nM/mM and 6.0 nM/mM creatinine, respectively. The majority of subjects showed diurnal variation, with mean afternoon values 15% lower than morning values (P <.0001 for afternoon vs morning values). The mean difference in DPD after 60 weeks was 1.67 nM/mM for morning and 1.34 nM/mM for afternoon creatinine. This difference was not significant. Some individuals displayed marked changes in DPD excretion with no change in health status or treatment. DPD excretion in a nonfasting afternoon sample showed similar characteristics to morning void samples in terms of scatter, week-to-week variation, and long-term reproducibility.

CONCLUSIONS

The study was set up to provide background data to assist the development of a clinical osteoporosis service for older women. Further studies are needed to determine whether these measurements predict fracture risk and respond to treatment changes in this age group.

Assessment and Recommendations on Factors Contributing to Preanalytical Variability of Urinary Pyridinoline and Deoxypyridinoline

Background: Pyridinoline (PYD) and deoxypyridinoline (DPD) are two of the most extensively characterized biochemical bone markers, but the interpretation of results is hampered by biologic and other preanalytical variability. We reviewed factors contributing to preanalytical variation of pyridinium cross-links in urine.

Methods: We searched four databases for English-language reports on PYD and/or DPD in urine. Searches were restricted to humans, except for studies of stability, when the search was expanded to other species. The 599 identified articles were supplemented with references from those articles and with articles known to the authors.

Results: The mean reported within-day variability was 71% for PYD (range, 57–78%) and 67% for DPD (range, 53–75%). The mean interday variability was 16% for both DPD and PYD (range for PYD, 12–21%; range for DPD, 5–24%). The mean intersubject variabilities across studies were 26% for PYD (range, 12–63%) and 34% for DPD (range, 8–98%) for healthy premenopausal women and 36% (range, 22–61%) and 40%, (range, 27–54%) for postmenopausal women, respectively. Specimen instability and errors in creatinine measurements were additional sources of variability.

Conclusions: Intra- and intersubject variability can be reduced by collecting specimens at a specific time of the day and by maintaining similar patient status at each specimen collection regarding factors such as medications and dietary supplements.

Comparison of serum and urinary C-terminal telopeptide of type I collagen in aging, menopause and osteoporosis

BACKGROUND

Urinary C-terminal telopeptide of type I collagen (u-CTx) has been reported to be a sensitive biochemical marker of bone turnover. There have been two assays for urinary CTx, which are alpha-CTx and beta-CTx. A newly developed immunoassay for serum CTx (s-CTx) is now available for assessment of bone resorption. We evaluated the effects of aging, menopause, and osteoporosis on the measurements of serum CTx and compared them to urinary CTx assays.

METHODS

In 79 premenopausal healthy women, 80 postmenopausal healthy women, 61 osteoporotic patients with vertebral fractures and 34 osteoporotic patients with hip fractures, s-CTx and urinary beta-CTx (u-betaCTx) were measured by ELISAs, and urinary alpha-CTx (u-alphaCTx) was measured by an RIA.

RESULTS

In all subjects, s-CTx significantly correlated with both u-alphaCTx (r=0.54) and u-betaCTx (r=0.51). There was no significant difference among s-CTx, u-alphaCTx and u-betaCTx in the T-scores of the postmenopausal group over the premenopausal group. These findings indicate that the value of s-CTx, as well as urinary CTxs, reflected the increase of bone resorption associated with menopause with a high degree of sensitivity. Patients with vertebral fractures had moderately increased concentrations of bone resorption markers compared to age-matched healthy postmenopausal women (T-score; s-CTx: 0.8, u-alphaCTx: 0.9, u-betaCTx: 0.7), whereas bone resorption markers in hip fracture patients were greatly increased compared to healthy postmenopausal women (T-score; s-CTx: 1.1, u-alphaCTx: 1.3 u-betaCTx: 1.3). The T-scores of u-CTxs against the postmenopausal group in vertebral fracture group and in hip fracture group were not significantly different from those of s-CTx.

CONCLUSIONS

s-CTx, as well as urinary CTxs, reflects the increase of bone resorption in patients with vertebral fractures and hip fractures.

Role of biochemical markers in the management of osteoporosis

Several serum and urine biochemical markers of bone resorption and formation have been developed. Biochemical bone markers have been used as intermediate end-points in all major studies of anti-osteoporotic therapies. Bone resorption markers, in particular, may add an independent, predictive value to the assessment of bone loss and fracture risk. There are also potential advantages in monitoring anti-osteoporotic treatment in the short-term in addition to bone densitometry, to rapidly identify non-responders to therapy, or non-compliance. Despite these recent advances, until now bone markers have simply been very useful research tools, with their clinical utility being limited by intra-individual and diurnal variability. However, the probability of the true bone mineral density response to hormone replacement therapy for the individual patient may be predicted using algorithms based on a spectrum of cut-off bone marker levels with varying false positive and negative rates. Thus, the transition of biochemical bone markers into everyday clinical practice may be rapidly approaching.

Changes in biochemical markers of bone metabolism and BMD during the first year after a hip fracture

We measured the levels of biochemical markers of bone formation and bone resorption in hip fracture patients preoperatively and after 6 and 12 months. Bone densitometry was done with quantitative computer tomography (QCT), dual-energy X-ray absorptiometry (DXA) and heel ultrasound. After 6 months, the biochemical markers of bone formation and bone resorption had increased. The levels remained high after 1 year and no change occurred between 6 and 12 months. We found no correlations between biochemical bone markers and bone density/stiffness on admission and change in bone mineral density (BMD) during the first postoperative year, despite the changes in bone markers and bone density. In our opinion, biochemical bone markers can not be used to predict bone loss in the individual patient after a hip fracture.

Biochemical bone markers and bone density in hip fracture patients: weak correlation in 106 women

Biochemical markers of bone formation and bone resorption were measured preoperatively, within 18 hours after a hip fracture (n 106) and bone mineral density (BMD) was measured with quantitative computer tomography (QCT), dual-energy x-ray absorptiometry (DXA) and heel ultrasound in 63 hip fracture patients. Patients with pertrochanteric fractures had more osteoporosis in all measurements than patients with femoral neck fractures. We found no differences in biochemical markers of bone formation or bone resorption in patients with femoral neck fractures and in those with pertrochanteric fractures. Correlations between biochemical bone markers and bone density, bone mass and stiffness on admission were weak.

Down-regulation of the serum stimulatory components of the insulin-like growth factor (IGF) system (IGF-I, IGF-II, IGF binding protein [BP]-3, and IGFBP-5) in age-related (type II) femoral neck osteoporosis

Both a decrease in bone formation and an increase in bone resorption have been implicated in the pathogenesis of age-related (type II) femoral neck osteoporosis. While the increase in the bone resorption rate has been shown to be partially related to secondary hyperparathyroidism, the mechanisms underlying the decline in bone formation have not yet been identified. The aim of the present study was to test the hypothesis that the bone formation deficit associated with type II osteoporosis might be due to secondary hyperparathyroidism and/or to a deficiency of the insulin-like growth factor (IGF) system. Circulating concentrations of IGF-I, IGF-II, IGF binding protein (IGFBP)-3, IGFBP-4, IGFBP-5, 25-hydroxycholecalciferol (25(OH)D3), and intact parathyroid hormone (PTH) were measured in 50 elderly women after sustaining a hip fracture and in 50 healthy age-matched controls. In addition, serum levels of osteocalcin (OC), skeletal alkaline phosphatase, and N-terminal procollagen peptide and urinary pyridinium cross-links were determined as markers of bone remodeling, and bone mineral density (BMD) was assessed at the proximal femur. In the patient group, serum was drawn within 18 h of the fracture and prior to surgery. Circulating protein concentrations did not change over this time frame. No difference was found between mean IGFBP-4 serum levels in the two groups studied, while mean levels of IGF-I, IGF-II, IGFBP-3, IGFBP-5, 25(OH)D3, and markers of bone formation were significantly lower (p < 0.006) in patients as compared with healthy subjects. Serum PTH and urinary pyridinium cross-links, however, were markedly increased (p < 0.001) in the osteoporotic group. In pooled data from the normal and osteoporotic populations, age-adjusted multiple regression models based on IGF-I, IGF-II, IGFBP-3, and IGFBP-5 were found to be highly predictive of serum OC (R2 = 19%, p < 0.001) and BMD of femoral neck (R2 = 49%, p < 0.0001), consistent with an effect of the anabolic IGF components on overall bone formation rate. Similar models based on 25(OH)D3 and PTH, however, were statistically unrelated to OC. To address further the potential impact of trauma on circulating IGF system components, we measured IGF system component levels in 10 male patients within 18 h following tibial fracture and in 10 age-matched normal male subjects. There was no significant difference in serum level of any of the IGF system components between the two groups. Although limited by its cross-sectional design, the present study suggests that, in addition to bone resorption resulting from secondary hyperparathyroidism, impaired bone formation associated with deficiency of the IGF system might predispose elderly women to fragility fracture of the proximal femur.

Dietary change and stable isotopes: a model of growth and dormancy in cave bears

In order to discuss dietary change over time by the use of stable isotopes, it is necessary to sort out the underlying processes in isotopic variation. Together with the dietary signal other processes have been investigated, namely metabolic processes, collagen turnover and physical growth. However, growth and collagen turnover time have so far been neglected in dietary reconstruction based on stable isotopes. An earlier study suggested that cave bears (Ursus spelaeus) probably gave birth to cubs during dormancy. We provide an estimate of the effect on stable isotopes of growth and metabolism and discuss collagen turnover in a population of cave bears. Based on a quantitative model, we hypothesized that bear cubs lactated their mothers during their first and second winters, but were fed solid food together with lactation during their first summer. This demonstrates the need to include physical growth, metabolism and collagen turnover in dietary reconstruction. Whereas the effects of diet and metabolism are due to fractionation, growth and collagen turnover are dilution processes.

Biochemical markers of bone turnover

Biochemical markers of bone turnover that are specific to bone allow study of the subtle changes in bone turnover associated with osteoporosis. They have been evaluated in Paget's disease of the bone and chronic renal failure. This review focuses on the use of biochemical markers of bone turnover in osteoporosis. The data in this review period are numerous and varied due to the growing interest in the use of biochemical markers of bone turnover in clinical practice. The data provide support for the use of the newer bone turnover markers for monitoring treatment of osteoporosis, if care is taken to minimize sources of variability.

Bone turnover and its relationship with bone mineral density in pre- and postmenopausal women with or without fractures

OBJECTIVE

This work was carried out in order to investigate possible relationships between bone turnover rate, as evaluated by bone biomarkers and skeletal mass, as evaluated by bone mineral density (BMD).

METHOD

Fifty-eight normal women and 30 female patients with osteoporotic fractures were enrolled. Three groups were defined: (1) fertile subjects (n = 24), mean age 33.7 +/- 8.1 years; (2) postmenopausal women (n = 32, including 11 patients with fractures) whose BMD values, in terms of T score, were less than -2.5 S.D. below the young adult mean obtained in our laboratory (mean age 61.7 +/- 7.9 years; and years since menopause (ysm), 12.6 +/- 8.3); (3) postmenopausal women (n = 32, including 19 patients with fractures) whose BMD values in terms of T score, were below -2.5 S.D. (mean age 62.9 +/- 8.6 years; and ysm 15.9 +/- 9.0). Groups II and III characterised, by inclusion criteria, by significant different mean BMD values, were similar as far as chronological and menopausal age were considered. Metabolic tests included a short urine collection to determine calcium, hydroxyproline, cross-linked N-telopeptides of type I collagen (NTx) and creatinine (Cr); half-way through this collection, a blood sample was taken for the measurement of total alkaline phosphatase activity (ALP) and tartrate-resistant acid phosphatase activity (TRAP). BMD at lumbar spine was evaluated.

RESULTS

There were significant differences amongst the three groups in mean ALP (P < 0.001, by analysis of variance) TRAP (P < 0.006) and NTx/Cr (P < 0.001) values, but not as far as mean values of calcium/Cr or hydroxyproline/Cr ratios were concerned. Considering the group as a whole, there were significant inverse correlations between NTx/Cr, ALP, TRAP and BMD controlling for both age (r = -0.392, P < 0.001; r = -0.447, P < 0.001 and r = -0.327, P < 0.002, respectively) and ysm (r = -0.374, P < 0.001; r = -0.474, P < 0.001 and r = -0.333, P < 0.002).

CONCLUSIONS

Our results indicate, that, even after controlling for both ageing and oestrogen status, there is an inverse relationship between bone mass (that at a given time represents the balance of all previous metabolic events) and a biochemical marker (which reflects bone turnover at the time of examination). These findings are in line with the belief that increased bone turnover should be regarded as a risk factor for osteoporosis. Furthermore, our results indicate that, unless there is no increase of hepatic isozyme, total ALP still maintains a possible role as a first analysis to evaluate bone turnover before requesting markers with greater specificity, sensitivity but also more expensive and whose analysis is sometimes time-consuming.

Biochemical markers of bone turnover. Applications for osteoporosis

The recent discovery of specific and sensitive biochemical markers reflecting the overall rate of bone formation and bone resorption has markedly improved the noninvasive assessment of bone turnover in various metabolic bone diseases, especially in osteoporosis. The immunoassay of human osteocalcin, recognizing the intact molecule and its major proteolytic fragment, and assays for bone alkaline phosphatase and the intact form of the N-terminal extension propeptide of type I collagen are currently the most sensitive markers for assessing bone formation. The best indices of bone resorption are the new immunoassays for pyridinoline cross-links and type I collagen-related peptides in urine and, recently, in serum. Several studies indicate that screening for these bone markers may be useful for improving the prognostic assessment of postmenopausal women in combination with bone mass measurement, that is, their risk for osteoporosis and, ultimately, for fractures and to monitor rapidly the efficacy of antiresorptive drugs.

Postmenopausal bone remodelling and hormone replacement

Osteoporosis is a serious, frequently occurring disease. Sensitive, specific and precise biochemical measures of bone remodelling, thus, are important tools in the evaluation of bone loss, fracture risk and treatment response. Bone turnover is predictive of the subsequent rate of loss. A high bone turnover documented by increased levels of biochemical markers predicts an increased rate of loss in bone mass. Additionally, as a high bone turnover leads to an increase in the extent of bone resorption as well as an increase of the erosion depth, this may also cause deterioration of the bone structure, thereby leading to an increased risk of fracture. That the predictive values of bone mass and markers of bone turnover are additive suggests that these measures describe different properties of bone. Hormone replacement induces a reduction in postmenopausal bone turnover, arrests loss of bone mass and decreases fracture risk. The skeletal response to therapy is reflected by bone markers and these may be used for monitoring purposes. Those who are in most need of treatment can be identified by a combination of bone mass and bone marker measurement. Furthermore, those who need the treatment most will demonstrate the best response in terms of bone mass. Concern has arisen because of a relatively large day-to-day variation, especially in urinary markers; however, this seems to be resolved through use of the new serum markers.

Vitamin D and bone mineral density

Bone mineral density (BMD) at the lumbar spine and the neck of femur and serum concentrations of 25-hydroxyvitamin D (25OHD), intact parathyroid hormone (PTH), alkaline phosphatase, calcium, albumin, creatinine and phosphate were measured in a group of 166 postmenopausal women (30-79 years) attending a bone clinic for bone density measurements. Four subjects with suspected primary hyperparathyroidism were excluded from analysis. BMD at the lumbar spine was correlated with body mass index (BMI) (r = 0.278, p = 0.0003), age (r = -0.194, p = 0.0134) and serum 25OHD (r = 0.188, p = 0.0167). BMD at the neck of femur correlated with BMI (r = 0.391, p < 0.0001), age (r = -0.356, p < 0.0001), PTH (r = -0.156, p = 0.047) and serum 25OHD (r = 0.231, p = 0.0031). Stepwise multiple regression analysis showed that age, BMI and serum 25OHD contributed to the variation in BMD at lumbar spine. At the neck of femur, PTH was an additional contributor. We conclude that serum 25OHD makes a contribution to BMD a lumbar spine and neck of femur.

Age-related (type II) femoral neck osteoporosis in men: biochemical evidence for both hypovitaminosis D- and androgen deficiency-induced bone resorption

The problem of osteoporosis in men has recently been recognized as an important public health issue. To test the hypothesis that endocrine deficiency-mediated alterations in bone metabolism might contribute to osteoporotic fracture risk in elderly men, serum levels of 25-hydroxycholecalciferol (25(OH)D), 1,25-dihydroxycholecalciferol (1,25(OH)2D), intact parathyroid hormone (PTH), testosterone, and estradiol were measured in 40 males (mean age 73 years) who were consecutively recruited within 18 h following a fracture of the proximal femur, and in an equal number of community-living older men (mean age 72 years) who served as controls. In addition, circulating osteocalcin and urinary excretion of (deoxy)pyridinoline were determined as markers of bone formation and resorption, respectively. No differences were observed between the mean serum concentrations of osteocalcin and estradiol. Serum levels of 25(OH)D, 1,25(OH)2D, and testosterone, however, were decreased in hip fracture patients. When correcting for differences in vitamin D binding protein, differences in 1,25(OH)2D did not persist, whereas serum 25(OH)D was still significantly lower in patients than in controls (6.1 +/- 4.3 vs. 7.6 +/- 2.8, p = 0.01). Similarly, a highly significant deficit was observed in the free testosterone index, calculated from total testosterone and the level of sex hormone binding globulin (2.6 +/- 1.3 vs. 8.2 +/- 2.9, p < 0.001). Serum PTH and urinary pyridinium cross-links, however, were markedly increased in the fracture group. Moreover, in fracture patients, free 25(OH)D and free testosterone were both significant and mutually independent negative predictors of (deoxy)pyridinoline excretion. Although limited by its cross-sectional design, the present study suggests that both hypovitaminosis D and androgen deficiency may predispose to bone resorption in elderly men and in turn to remodeling imbalance and fracture risk.

Decrease of bone formation in adult women with fragility fractures

OBJECTIVES

To compare bone mineral density (BMD) and some markers of bone metabolism in women with fragility fractures and in normal age-matched subjects.

METHODS

A 100 women with at least one vertebral deformity > 25%, and 219 age-, BMI- and parity-matched healthy women, were recruited for the study. In all the patients fractures were symptomatic and occurred at least 1 year before densitometric measurement. Forearm bone mineral density (BMD) as well as biochemical assessment of some markers of bone turnover were measured in all the subjects.

RESULTS

BMD was significantly lower in the fracture than in the control group (0.326 +/- 0.073 vs. 0.379 +/- 0.079; P < 0.001). Fractured women showed alkaline phosphatase (ALP) and osteocalcin (OC) serum levels significantly lower than controls, while no differences were found in fasting urinary calcium and hydroxyproline excretion. Women without fractures showed a significant correlation between ALP and both age and years since menopause (YSM). Such a correlation is lacking in the fracture group.

CONCLUSIONS

Women with vertebral deformities likely due to a fracture had a forearm BMD and markers of bone formation lower than normal. Whether low bone density is due to a low peak of bone mass or to an increased postmenopausal bone loss sustained by an uncoupling between the two bone remodelling processes is still unclear.

Bone markers

The recent development of specific and sensitive biochemical markers reflecting the overall rate of bone formation and bone resorption, has markedly improved the non-invasive assessment of bone turnover in various metabolic bone diseases, especially osteoporosis. The immunoassay of human osteocalcin recognizing the intact molecule and its major proteolytic fragment, along with that of bone alkaline phosphatase, are currently the most sensitive markers to assess bone formation. For bone resorption, the total urinary excretion of pyridinoline crosslinks measured by high pressure liquid chromatography has shown its superiority over all other markers for the clinical assessment of osteoporosis. The recent development of immunoassays recognizing either the free pyridinoline crosslinks or pyridinoline crosslinked-type I collagen peptides in urine and serum should allow a broad use of this sensitive resorption marker. Recent studies, some of them still in progress, define the clinical use of these markers: first, to improve the prognostic assessment of post-menopausal women in combination with bone mass measurement, i.e. their risk of developing osteoporosis and, ultimately, fractures and, second, to monitor the efficacy of anti-resorption drugs.

Relationship of bone turnover to bone density and fractures

To assess the influence of bone turnover on bone density and fracture risk, we measured serum levels of osteocalcin (OC), bone alkaline phosphatase (BAP), and carboxy-terminal propeptide of type I procollagen (PICP), as well as 24-h urine levels of cross-linked N-telopeptides of type I collagen (NTx) and the free pyridinium cross-links, pyridinoline (Pyd) and deoxypyridinoline (Dpd), among 351 subjects recruited from an age-stratified random sample of Rochester, Minnesota women, PICP, NTx, and Dpd were negatively associated with age among the 138 premenopausal women. All of the biochemical markers were positively associated with age among the 213 postmenopausal women, and the prevalence of elevated turnover (> 1 standard deviation [SD] above the premenopausal mean) varied from 9% (PICP) to 42% (Pyd). After adjusting for age, most of the markers were negatively correlated with bone mineral density (BMD) of the hip, spine, or forearm as measured by dual-energy X-ray absorptiometry, and women with osteoporosis were more likely to have high bone turnover. A history of osteoporotic fractures of the hip, spine, or distal forearm was associated with reduced hip BMD and with elevated Pyd. After adjusting for lower BMD and increased bone resorption, reduced bone formation as assessed by OC was also associated with prior osteoporotic fractures. These data indicate that a substantial subset of elderly women has elevated bone turnover, which appears to adversely influence BMD and fracture risk. Combined biochemical and BMD screening may provide better prediction of future fracture risk than BMD alone.

Changes in bone collagen markers and in bone density in hormone treated and untreated postmenopausal women

OBJECTIVE

This study aims to compare bone mineral density measurements (BMD), pyridinium crosslink levels and pyridinium crosslink levels in untreated and hormone treated postmenopausal women.

METHODS

A cross-sectional study comparing biophysical (BMD) and biochemical (pyridinium crosslink and PCICP) parameters in a group of untreated postmenopausal women (n = 145) to a group of postmenopausal women on hormone replacement therapy (HRT) (n = 92).

RESULTS

Untreated postmenopausal women compared to postmenopausal women on HRT had higher Osteoblastic and Osteoclastic activity. Procollagen I C-end terminal peptide (PCICP) was 11.3% lower in the women on HRT compared to controls whilst crosslinks were 27.2% lower than in controls. This seems to indicate that women on HRT had a bone balance that was higher compared to the control group (15.9%). The difference in bone density of L2-L4 between the two groups was (16.1%).

CONCLUSIONS

This study seems to indicate that postmenopausal women receiving HRT readjust their bone remodelling so that although osteoblastic function is reduced, there is a much greater deduction in osteoclastic function and this results in an overall higher bone mass observed in the BMD of women on HRT.

Evaluation of bone turnover in postmenopause, vertebral fracture, and hip fracture using biochemical markers for bone formation and resorption

The purpose of this study is to evaluate bone turnover in postmenopausal status and established osteoporosis with vertebral fracture and hip fracture by assessing bone biochemical markers. Subjects were 50 healthy premenopausal subjects, 44 healthy postmenopausal subjects, 30 osteoporotic patients with vertebral fracture, and 31 osteoporotic patients with hip fracture. Alkaline phosphatase, osteocalcin, PICP, ICTP, NTx, free deoxypyridinoline, total pyridinoline and deoxypyridinoline were measured. In postmenopause, both Z-scores of bone formation markers and resorption markers were around 1-2. In osteoporosis, although Z-scores of bone formation markers were 0.4-2.8, resorption markers were 2.3-9.5. Moreover, Z-scores of resorption markers were higher in hip fracture than in vertebral fracture. These results indicate that bone formation and resorption increased and balanced in postmenopausal status. However, bone resorption increased more than bone formation and did not balance at all in osteoporosis. This imbalance is greater in hip fractures than in vertebral fractures.

Clinical epidemiology and osteoporosis. Measures and their interpretation

Identifying patients with a high risk of fracture and monitoring a patient's therapeutic response are important. Current methods to evaluate the risk of fracture include the measurement of bone mineral density as well as other risk factors, including those associated with the risk of falling. Several considerations are important in defining the risk for fracture. There is currently no level of bone mineral density at which the risk of fracture is zero, that is, some high-risk women will not have a fracture and some low-risk women will. The monitoring of high-risk individuals for subtle changes in their bone status is not economically feasible at this time. Given the precision of current measurement technology, it is more reasonable to expect to monitor individuals on a 3- to 5-year basis rather than every 6 months to 1 year. There is no single optimal site at which measurement is highly precise and predictive of bone mineral density measurement at other skeletal locations. Currently, measurement of the femoral neck seems to have the most universal applicability. Measurement of bone turnover markers remains more effective as a research tool and is less effective as a method to diagnose or monitor the bone status of individual patients.

Longitudinal evaluation of a bone resorption marker in elderly subjects

The variability over time in the excretion of a bone resorption metabolite (collagen type I N-telopeptide crosslink, NTx) was evaluated in a cohort of community-dwelling elderly men and women (mean age 73 years). Three annual 24-h urine samples were collected. NTx concentration was measured using an established ELISA. Total (24-h) NTx excretion as well as Ntx/creatinine concentration were compared. Men had a significantly lower excretion of NTx/creatinine than women who were not on hormone replacement therapy. Overall, the within-subject long-term coefficient of variability for Ntx/creatinine was 26%. The correlation coefficient between the samples taken a year apart was higher for the 24-h NTx excretion (r = 0.66) than for the 24-h creatinine excretion (r = 0.51). The consistency of NTx excretion over time was also evaluated in all 93 subjects with three yearly samples using Kendall's rank correlation method; the resulting coefficient of concordance was 0.78 (significant at the 0.01 level). These results indicate that while NTx excretion varies in subject samples collected over a period of 2 years, this variability is not much greater than the daily variation reported for NTx and other bone metabolism markers. The relative reproducibility of NTx excretion over time in this age group was also evident in the coefficient of concordance. The results provide support for stratifying subjects according to level of bone resorption and identifying those subjects with high turnover who may be at greater risk of osteoporotic fracture.

Markers of bone resorption predict hip fracture in elderly women: the EPIDOS Prospective Study

Increased bone turnover has been suggested as a potential risk factor for osteoporotic fractures. We investigated this hypothesis in a prospective cohort study performed on 7598 healthy women more than 75 years of age. One hundred and twenty-six women (mean years 82.5) who sustained a hip fracture during a mean 22-month follow-up were age-matched with three controls who did not fracture. Baseline samples were collected prior to fracture for the measurement of two markers of bone formation and three urinary markers of bone resorption: type I collagen cross-linked N- (NTX) or C-telopeptide (CTX) and free deoxypyridinoline (free D-Pyr). Elderly women had increased bone formation and resorption compared with healthy premenopausal women. Urinary excretion of CTX and free D-Pyr, but not other markers, was higher in patients with hip fracture than in age-matched controls (p = 0.02 and 0.005, respectively). CTX and free D-Pyr excretion above the upper limit of the premenopausal range was associated with an increased hip fracture risk with an odds ratio (95% confidence interval) of 2.2 (1.3-3.6) and 1.9 (1.1-3.2), respectively, while markers of formation were not. Increased bone resorption predicted hip fracture independently of bone mass, i.e., after adjustment for femoral neck bone mineral density (BMD) and independently of mobility status assessed by the gait speed. Women with both a femoral BMD value of 2.5 SD or more below the mean of young adults and either high CTX or high free D-Pyr levels were at greater risk of hip fracture, with an odds ratio of 4.8 and 4.1, respectively, than those with only low BMD or high bone resorption. Elderly women are characterized by increased bone turnover, and some markers of bone resorption predict the subsequent risk of hip fracture independently of hip BMD. Combining the measurement of BMD and bone resorption may be useful to improve the assessment of the risk of hip fracture in elderly women.

New developments in biochemical markers for osteoporosis

The noninvasive assessment of bone turnover has markedly improved in the past few years with the development of sensitive and specific markers of bone formation and bone resorption. Markers of bone formation in serum include total and bone-specific alkaline phosphatase, osteocalcin, and type I collagen carboxyterminal extension peptide. Assessment of bone resorption can be achieved by measuring plasma tartrate-resistant acid phosphate and the urinary excretion (and possibly serum levels) of bone type I collagen degradation products: hydroxyproline, hydroxylysine glycosides, and, more recently, the pyridinium crosslinks (pyridinoline and deoxypyridinoline) and associated peptides. The immunoassay of human osteocalcin and bone alkaline phosphatase for formation and the pyridinoline crosslinks measured by high-pressure liquid chromatography or by immunoassay for bone resorption are currently the most sensitive and specific markers of bone turnover for the clinical assessment of osteoporosis. Using these new markers, several studies have shown that bone turnover increases after the menopause and remains elevated in late postmenopausal and elderly women. An increased bone turnover rate is related to a high rate of bone loss in postmenopausal women and to a decreased bone mass in elderly women. Recent data suggest that some of the new immunoassays for pyridinoline crosslinks could predict the subsequent risk of hip fracture in elderly women. Thus, bone markers might be used in combination with bone mass measurement to improve the prognostic assessment of postmenopausal women, i.e., their risk of developing osteoporosis and ultimately fractures. Treatment of postmenopausal women with antiresorptive drugs such as estrogens, bisphosphonates, and calcitonin induces a rapid decrease in the levels of bone markers that is correlated with the long-term effect of such treatments on bone mass. Thus, bone markers should be very useful in monitoring treatment efficacy in patients with osteoporosis.

Age-related bone loss and senile osteoporosis: evidence for both secondary hyperparathyroidism and skeletal growth factor deficiency in the elderly

Aging is characterized by a decrease in bone volume, implying that net bone resorption exceeds net bone formation. This age-related bone loss can be regarded as the main determinant of hip fracture risk in the elderly. In the concept of senile osteoporosis, a key role has been attributed to vitamin D deficiency. Lack of vitamin D activity may affect femoral strength through impaired mineralization as well as through a hyperparathyroidism-mediated increase in bone resorption. In addition to vitamin D-related mechanisms, recent evidence has indicated a decline in the skeletal content of anabolic growth factors--such as insulin-like growth factor-I (IGF-I)--in femoral (cortical) bone, suggesting that skeletal growth factor deficiency may contribute to the age-related bone loss in the proximal femur as well. It is tempting to speculate that skeletal IGF-I loss might, at least partially, be accounted for by growth hormone deficiency. However, critical evidence does not yet support the concept that the decreased activity of the growth hormone-IGF-I-axis alters bone remodeling, and the extent to which serum concentrations of growth factors are reflective of skeletal activity remains to be clarified.

Assessment of biochemical markers of bone metabolism in relation to the occurrence of fracture: a retrospective and prospective population-based study of women

We have in a population-based setting evaluated biochemical markers of bone metabolism in 328 women, aged 40-80 years, and related it to contents of bone mineral measurements and the retrospective and prospective presence of fracture. The participants were recruited from the city population files. Serum samples for analysis of osteocalcin (Oc), procollagen I carboxy-terminal extension peptide (PICP), and carboxy-terminal telopeptide of type I collagen (ICTP) were taken, and forearm bone mineral content (BMC) was measured by single photon absorptiometry (SPA). Fracture history was recorded, and the information was verified and supplemented from both radiologic and orthopedic files. Five years later the registration of fractures was repeated. At the initial investigation, Oc was 23% lower in women who had sustained a fracture (n = 37) within 6 years before measurement (6.3 +/- 3.6 microgram/l vs 8.2 +/- 4.2 microgram/l (p = 0.006)), after adjusting for age and BMC difference. PICP and ICTP were not different from values in the women without fracture. However, in women aged 70-80 years with a fracture sustained during the previous 6 years, PICP was lower (128 +/- 32 microgram/l vs 144 +/- 34 microgram/l, p = 0.046). Oc and ICTP were significantly correlated to age and BMC (Oc-age r = 0.36, Oc-BMC r = -0.31, ICTP-age r = 0.44, ICTP-BMC r = -0.24). The correlations of PICP were weaker. Prospectively, logistic regression gave an odds ratio (OR) of 1.8 (p = 0.015) for a low PICP and fracture susceptibility, at a change of 1 SD, independent of age and BMC. In the age bracket 70-80, the odds ratio was 2.4 (p = 0.036). The odds ratio for ICTP, independent of age and BMC, was 1.9 (P = 0.043) for 1 SD decrease and subsequent fracture risk. We concluded that women who had sustained at least one recent fracture had an altered bone turnover with decreased bone formation but an unaltered resorption. Women with retrospectively registered fractures also sustained subsequent fractures. A decrease from the mean of the collagen markers PICP and ICTP was associated with an increased risk for future fracture. Utilizing these biochemical markers of bone metabolism in a female population, PICP and ICTP had a similar influence on the risk of future fracture as forearm BMC (OR = 1.6, p = 0.03).

Increased bone resorption and decreased bone formation in Chinese patients with hip fracture

Biochemical markers of bone formation (bone-specific alkaline phosphatase and osteocalcin) and bone resorption (hydroxyproline excretion and bone isoenzyme of acid phosphatase) were measured in 30 patients (15 M and 15 F) with hip fracture and 30 healthy subjects matched for age and sex. Bone isoenzyme of tartrate-resistant acid phosphatase (TRACP) was measured by a recently developed specific immunoassay. Serum osteocalcin concentration and bone-specific alkaline phosphatase activity were significantly lower and serum TRACP concentration and urinary hydroxyproline excretion were elevated in patients compared with healthy subjects. We suggest that there is reduced bone formation and increased bone resorption in patients with hip fracture.

Biochemical markers of bone turnover

The noninvasive assessment of bone turnover has received increasing attention over the past few years because of the need for sensitive markers in the clinical investigation of osteoporosis. Markers of bone formation include the serum measurement of total and bone-specific alkaline phosphatase, osteocalcin, and type I collagen extension peptides. Assessment of bone resorption can be achieved with measurement of fasting urinary calcium and hydroxyproline, urinary hydroxylysine glycosides, urinary excretion of the pyridinium cross-links (pyridinoline and deoxypyridinoline), and plasma tartrate-resistant acid phosphatase activity. Several studies performed in a variety of metabolic bone diseases have shown these markers to be of unequal sensitivity and specificity. In addition, some of them are not fully characterized. For assessment of the level of bone turnover in women with vertebral osteoporosis, serum osteocalcin and urinary pyridinoline appear to be the most sensitive markers so far. Programs combining bone mass measurement and assessment of bone turnover by several markers in women at the time of menopause are being developed in an attempt to improve the assessment of the risk for osteoporosis. Efforts are being made to develop more convenient assays and to identify other markers of bone turnover. A battery of various specific markers is likely to improve the assessment of the complex and subtle abnormalities of bone metabolism that characterize metabolic bone diseases, especially the various aspects of osteoporosis.