Spurious Hyperphosphatemia in a Patient with Chronic Kidney Disease - a Rare Case of Alteplase Contamination

Spurious hyperphosphatemia, a rare occurrence, typically arises from substances in a patient's blood interfering with the colorimetric method for serum phosphate measurement. We present a case of factitious hyperphosphatemia caused by alteplase-contaminated blood samples in an 88-year-old CKD patient on hemodialysis, leading to misleadingly high phosphorus levels. Thorough investigations ruled out other etiologies, highlighting the necessity of stringent adherence to blood collection protocols to prevent sample contamination and avert erroneous laboratory results. This unique cause of hyperphosphatemia should be considered in the differential diagnosis when encountering unexplained elevations in phosphorus levels, particularly in the context of normal blood calcium levels.

Evaluation of methods to eliminate analytical interference in multiple myeloma patients with spurious hyperphosphatemia

OBJECTIVE

The acid/molybdate assay performed on the Beckman Coulter AU5821 could be subject to paraprotein interference, which potentially results in spurious hyperphosphatemia. We attempted to find a reliable solution to eliminate paraprotein interference in laboratory test results and discuss the causes of paraprotein interference.

METHODS

We observed 50 multiple myeloma patients with serum paraproteins. We used the trichloroacetic acid (TCA) deproteinizing method to confirm that paraproteins indeed interfered with phosphate detection in the serum acid/molybdate assay. Furthermore, we used the dry chemical method (Vitros 5.1 FS, Johnson) and deionized water (H2O), normal saline (NS), and healthy human serum as alternative diluents. We assessed the clinical acceptability of the 4 methods by evaluating a bias percentage (bias%) lower than 10% under the premise of TCA treatment as a serum phosphate reference method.

RESULTS

In total, comparing the results of the TCA treatment on the Beckman Coulter AU5821, 3/50 (6%) multiple myeloma patients exhibited phosphate pseudo-elevation (bias% >10%). Additionally, we found pseudo-hypophosphate only in immunoglobulin (Ig)G-kappa paraprotein samples, and all were above 50 g/L. The bias% between TCA and dry chemical method for the 3 patients was below 10%. The maximum acceptable dilutions for patient 22 were 8-fold H2O, 4-fold H2O , and 2-fold serum; those for patient 45 were 16-fold H2O, 16-fold H2O, and 2-fold serum. However, the bias% of patient 40 was beyond the acceptable range in all 3 dilution groups.

CONCLUSION

High concentrations of IgG kappa-type paraproteins are more likely to interfere with serum phosphorous detection. Both the TCA and dry chemical method can effectively eliminate paraprotein interference.

Health Economic Benefits of Introducing Sucroferric Oxyhydroxide in the Treatment of Patients with Chronic Kidney Disease under Dialysis in the Kingdom of Saudi Arabia

Hyperphosphatemia is an electrolyte disorder highly prevalent in patients with chronic kidney disease undergoing hemodialysis (HD) that usually requires treatment with oral phosphate binders (PBs). Sucroferric oxyhydroxide (SO) is a calcium-free, iron-based PB indicated for the control of serum phosphorus. In the real-world setting, SO has shown clinical effectiveness with a lower pill burden and has also been associated with reduced hospital admission rates. This study aims to assess the potential economic benefits resulting from the introduction of SO to the health-care setting of the Kingdom of Saudi Arabia (KSA). An economic analysis using data from a retrospective real-world study that compared HD patients with uninterrupted SO prescriptions with patients who discontinued SO and switched to other PBs (oPBs). Annual drug costs for the estimated PB-eligible population in KSA were quantified. Costs per responder were estimated for all treatments. Hospital admissions' incidence rates were converted into annual inpatient cost savings and were deducted from drug costs to estimate the annual economic effect of SO versus oPBs. Sensitivity and breakeven analyses were also conducted. The eligible population for PB therapy in KSA was estimated at n = 14,748. Treating therapy-eligible populations exclusively with SO was estimated to generate annual inpatient cost-savings of SAR 107.4-119.4 million compared to treating the population with oPBs. The estimated economic effect signified overall annual savings ranging from SAR 82.8 to SAR 94.8 million when the population is treated with SO. Sensitivity analyses showed persistent cost savings. The estimated benefit-cost ratios showed that for every SAR 1 spent on SO, the expected return on investment was SAR 4.4-4.9. SO is an effective therapy that may result in substantial cost savings from reducing hospital admission costs that are attributable to hyperphosphatemia among HD patients.

Use of Teriparatide in Hyperphosphatemic Familial Tumor Calcinosis: Evaluating the Interaction Between FGF23 and PTH on the Phosphaturic Effect

Hyperphosphatemic familial tumor calcinosis (HFTC) is a rare disease characterized by hyperphosphatemia and calcium and phosphorus crystal deposition. It occurs due to the loss of function of FGF23. Herein, we report a case of a 50-year-old woman diagnosed with HFTC (homozygous variant in the GALNT3 gene, c.803_804 C insertion) with a history of ectopic calcifications in the past 30 years. Laboratory tests on admission were as follows: phosphate (P) 7.1 mg/dL (Normal range (NR) 2.5-4.5 mg/dL), FGF23 c-terminal 2050 RU/mL (NR < 150 RU/mL), and intact FGF23 (iFGF23) 18.93 pg/mL (NR 12.0-69.0 pg/mL). Treatment with acetazolamide, sevelamer, and a phosphorus-restricted diet was started, but phosphatemia remained high and calcifications continued to progress. In an attempt to further decrease P, a 36-day cycle of teriparatide (TPTD) 20 mcg twice daily was added, decreasing P from 6.2 to 5.2 mg/dL and increasing the 1.25(OH)₂ vitamin D by 34.2%. As urinalysis was not feasible at the end of the 36-day cycle, a second cycle was performed for another 28 days, producing a similar decrease in P (from 6.4 to 5.5 mg/mL) and an evident decrease in the rate of tubular reabsorption of P (from 97.2 to 85.3%), however, accompanied by a worrying increase in calciuria. The use of TPTD 20 mcg twice daily in a patient with genetic resistance to FGF23 (HFTC) was associated with consistent increase in phosphaturia and reduction in phosphatemia, in addition to an increase in calcitriol. The resulting hypercalciuria precludes the therapeutic use of TPTD in HFTC and suggests an important role of FGF23, not only in phosphate homeostasis but also in avoiding any excess of calcitriol.

Transient Hyperphosphatasemia in a Child with Autism Spectrum Disorder

INTRODUCTION

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication and the presence of restricted interests and repetitive behaviors. Transient hyperphosphatasemia of infancy and early childhood (THI) is a benign laboratory disorder characterized by transiently extremely elevated activity of serum alkaline phosphatase (S-ALP).

CASE REPORT

We present a 21-month-old girl with a right leg limp, most probably due to reactive arthritis after febrile viral infection, and deterioration of psychomotor development with concomitant transient elevation of S-ALP (61.74 μkat/L; normal 2.36-7.68 μkat/L). Normal values of serum creatinine, aspartate-aminotransferase, alanin-aminotransferase, calcium, phosphate, together with normal wrist X-ray ruled out rickets or other bone or hepatic cause of high S-ALP. The S-ALP gradually decreased within 3 months, thus fulfilling the THI criteria. Screening for inborn errors of metabolism was negative and meticulous neurologic, psychologic and psychiatric assessment pointed to the diagnosis of autism spectrum disorder (ASD). There was no causal relationship between THI and ASD, as high S-ALP was an accidental and transient finding within the routine laboratory assessment. However, when THI occurs in a child with an onset of a new disorder, or with a pre-existing bone or liver disease, it might seriously concern the physician.

CONCLUSION

Children with THI should be spared from extensive evaluations and unnecessary blood draws.

LED&Paper-based analytical device for phosphatemia/calcemia diagnostics☆

In this communication a prototype of paper-based analytical device designed for simultaneous determination of orthophosphate and calcium ions, which levels are significant for hyperphosphatemia diagnostics, is presented. The laboratory-on-paper structure for two analytes detection was wax-printed on the surface of filter paper. These two-analyte disposable paper strips are combined with two paired LED-based fluorescence detectors and simple voltmeter used as recorder of analytical signal, what makes the developed device miniature, extremely low-cost, portable and user-friendly. Thus the developed device allows usage outside of specialized clinical laboratory. Moreover, each paper strip is disposable and its utilization is easy and fast and, additionally, burnt strip tests ensure waste non-infectious. The presented LED&Paper-based analytical device provides low detection limits: 1.4 μmol L^-1 and 7.4 μmol L^-1 for orthophosphate and calcium ions, respectively. The practical utility of the developed device for calcemia/phosphatemia diagnostics is demonstrated using control serum standards and real human serum.

Treatment of hyperphosphatemia: the dangers of aiming for normal PTH levels

Secondary hyperparathyroidism is part of the complex of chronic kidney disease-associated mineral and bone disorders (CKD-MBD) and is linked with high bone turnover, ectopic calcification, and increased cardiovascular mortality. Therefore, measures for CKD-MBD aim at lowering PTH levels, but there is no general consensus on optimal PTH target values. This manuscript is part of a pros and cons debate for keeping PTH levels within the normal range in children with CKD, focusing on the cons. We conclude that a modest increase in PTH most likely represents an appropriate adaptive response to declining kidney function in patients with CKD stages 2-5D, due to phosphaturic effects and increasing bone resistance. There is no evidence for strictly keeping PTH levels within the normal range in CKD patients with respect to bone health and cardiovascular outcome. In addition, the potentially adverse effects of PTH-lowering measures, such as active vitamin D and calcimimetics, must be taken into account. We suggest that PTH values of 1-2 times the upper normal limit (ULN) may be acceptable in children with CKD stage 2-3, and that PTH levels of 1.7-5 times UNL may be optimal in patients with CKD stage 4-5D. However, standard care of CKD-MBD in children relies on a combination of different measures in which the observation of PTH levels is only a small part of, and trends in PTH levels rather than absolute target values should determine treatment decisions in patients with CKD as recommended by the 2017 KDIGO guidelines.

Effect of Intradialytic Exercise on Hyperphosphatemia and Malnutrition

Intradialytic exercise (IDE) is not routinely prescribed in hemodialysis (HD) units despite its potential benefits on patients' outcomes. This study was the first in the United Arab Emirates to examine the effect of aerobic IDE on hyperphosphatemia, malnutrition, and other health outcomes among HD patients. Participants were chosen from the largest HD unit in Sharjah Emirate for a quasi-experimental intervention with pre and post evaluation. The study lasted for 12 months. Study parameters were collected at baseline, post intervention, and follow-up. The intervention included a moderate-intensity aerobic IDE of 45 min per HD session; intensity was assessed using the Borg Scale. Patients were educated on the importance of exercise. Study outcomes were serum phosphorus (P), malnutrition inflammation score (MIS), quality of life (QOL), and pertinent blood tests. Forty-one eligible consenting HD patients were included in the study. Results at follow-up showed a non-significant reduction in P (p = 0.06) in patients who were hyperphosphatemic at baseline, but not in the sample as whole. MIS did not deteriorate throughout the study (p = 0.97). IDE resulted in a non-significant increase in the QOL visual analogue scale (p = 0.34). To conclude, aerobic IDE for 45 min is safe and could be beneficial, especially for hyperphosphatemic patients.

Modeled Daily Ingested, Absorbed and Bound Phosphorus: New Measures of Mineral Balance in Hemodialysis Patients

BACKGROUND

Control of predialysis serum phosphorus in hemodialysis patients is challenging. We explored the utility of a novel kinetic phosphorus modeling program.

METHODS

As part of a quality assurance program, urea kinetic modeling results were combined with those from phosphorus kinetic modeling to compute modeled daily ingested phosphorus (DIP) and components making up this metric, including absorbed, bound, and nonabsorbed, nonbound phosphorus.

RESULTS

In 182 hemodialysis patients, DIP averaged 1,089 ± 348 mg/day in men and 934 ± 292 in women (p < 0.002) and correlated substantially with body weight. DIP/kg bodyweight (12.8 ± 3.40 mg/kg) was not significantly different between the sexes. Prescribed equivalent binder dose (EBD) was 4.98 ± 3.61 and 4.53 ± 3.02 g/day in men and women, respectively (p NS). Protein catabolic rate (PCR) was significantly higher in men (64.4 ± 18) g/day vs. women (48.2 ± 15.6, p < 0.001), and the DIP/PCR ratio was 17.4 ± 4.81 in men vs. 20.1 ± 5.76 in women (p < 0.001). Presence of residual kidney function was associated with a lower prescribed EBD dose (4.08 ± 2.62 vs. 5.38 ± 3.81 g/day, p < 0.01). Self-reported poor binder compliance was associated with higher DIP or DIP/kg as well as higher prescribed EBD. In anuric patients, DIP/kg was increased in patients consuming diets with high phosphate additive content and those reporting poor compliance with the prescribed dose of phosphate binders.

CONCLUSIONS

The combination of urea kinetic and phosphorus modeling can be used to estimate measures related to phosphorus intake. High DIP/PCR or DIP/kg body weight values in anuric patients suggest consumption of a diet high in phosphorus additives or noncompliance with the prescribed amount of phosphorus binders.

Hyperphosphatemic Familial Tumoral Calcinosis in Two Siblings with a Novel Mutation in GALNT3 Gene: Experience from Southern Turkey

Inactivating autosomal recessive mutations in fibroblast growth factor 23 (FGF23), klotho (KL) and polypeptide N-acetylgalactosaminotransferase 3 (GALNT3) genes lead to a rare disorder, hyperphosphatemic familial tumoral calcinosis (HFTC). Patients with HFTC present with hyperphosphatemia and tumor like soft tissue calcifications. Although 78% of patients develop their first symptoms between the ages of 2-13 years, diagnosis is usually delayed until adulthood. Some individuals with the same genetic defect develop a condition named hyperphosphatemic hyperostosis syndrome. Herein we report two siblings suffering from periarticular, warm, hard and tender subcutaneous masses. Subcutaneous calcifications were present on X-ray and biopsy results were consistent with calcinosis in both patients. Laboratory results showed marked hyperphosphatemia and elevated renal tubular phosphate reabsorption rates, normal renal function tests and normal serum 25-hydroxyvitamin D levels. Thus, we suspected HFTC and performed next generation sequencing for the GALNT3 gene, reported as the most frequent cause. A novel homozygote P85Rfs*6 (c.254_255delCT) mutation in GALNT3 was identified in both siblings. Our report adds two new patients to the literature about this rare genetic disease and suggests that small deletions in the GALNT3 gene may be related with HFTC phenotype.

The impact of a nutritional intervention based on egg white for phosphorus control in hemodialyis patients

BACKGROUND AND AIMS

Here we describe a dietary intervention for hyperphosphatemia in dialysis patients based on the partial replacement of meat and fish, which are one of the main sources of alimentary phosphorous, with egg white, a virtually phosphorous-free protein source. This intervention aims to reduce phosphorous intake without causing protein wasting.

PATIENTS AND METHODS

As many as 23 hyperphosphatemic patients (15 male and 8 female, mean age 53.0 ± 10.0 years) on chronic standard 4 h, three times weekly, bicarbonate hemodialysis were enrolled in this open-label, randomized controlled trial. Patients in the intervention group were instructed to replace fish or meat with egg white in three meals a week for three months whereas diet was unchanged in the control group.

RESULTS

Serum phosphate concentrations were significantly lower in the intervention group than in controls after three (4.9 ± 1.0 vs 6.6 ± 0.8; p < 0.001) but not after one month of treatment. Phosphate concentrations decreased more from baseline in the intervention than in the control group both after one (-1,2 ± 1,1 vs 0,5 ± 1,1; p = 0.004) and after three (-1,7 ± 1,1 vs -0,6 ± 1,1; p < 0.001) months of follow-up. No change either in body weight or in body composition assessed with bioelectrical impedance analysis or in serum albumin concentration was observed in either group.

CONCLUSION

The partial replacement of meat and fish with egg white induces a significant decrease in serum phosphate without causing protein malnutrition and could represent a useful instrument to control serum phosphate levels in hemodialysis patients. CLINICALTRIALS.

GOV IDENTIFIER

NCT03236701.

Control of metabolic predisposition to cardiovascular complications of chronic kidney disease by effervescent calcium magnesium citrate: a feasibility study

Aims

Cardiovascular (CV) complications are common in chronic kidney disease (CKD). Numerous metabolic disturbances including hyperphosphatemia, high circulating calciprotein particles (CPP), hyperparathyroidism, metabolic acidosis, and magnesium deficiency are associated with, and likely pathogenic for CV complications in CKD. The goal of this feasibility study was to determine whether effervescent calcium magnesium citrate (EffCaMgCit) ameliorates the aforementioned pathogenic intermediates.

Methods

Nine patients with Stage 3 and nine patients with Stage 5D CKD underwent a randomized crossover study, where they took EffCaMgCit three times daily for 7 days in one phase, and a conventional phosphorus binder calcium acetate (CaAc) three times daily for 7 days in the other phase. Two-hour postprandial blood samples were obtained on the day before and on the 7th day of treatment.

Results

In Stage 5D CKD, EffCaMgCit significantly increased T50 (half time for conversion of primary to secondary CPP) from baseline by 63% (P = 0.013), coincident with statistically non-significant declines in serum phosphorus by 25% and in saturation of octacalcium phosphate by 35%; CaAc did not change T50. In Stage 3 CKD, neither EffCaMgCit nor CaAc altered T50. With EffCaMgCit, a significant increase in plasma citrate was accompanied by statistically non-significant increase in serum Mg and phosphate. CaAc was without effect in any of these parameters in Stage 3 CKD. In both Stages 3 and 5D, both drugs significantly reduced serum parathyroid hormone. Only EffCaMgCit significantly increased serum bicarbonate by 3 mM (P = 0.015) in Stage 5D.

Conclusions

In Stage 5D, EffCaMgCit inhibited formation of CPP, suppressed PTH, and conferred magnesium and alkali loads. These effects were unique, since they were not observed with CaAc. In Stage 3 CKD, neither of the regimens have any effect. These metabolic changes suggest that EffCaMgCit might be useful in protecting against cardiovascular complications of CKD by ameliorating pathobiologic intermediates.

Design and baseline characteristics of the LANDMARK study

Background

Calcium (Ca)-based phosphate (P) binders, compared to non-Ca-based P binders, contribute to vascular calcification, which is associated with cardiovascular events.

Methods

The LANDMARK study is a multicenter, randomized, open-label, parallel comparative study of lanthanum carbonate (LC) and calcium carbonate (CC) in hemodialysis patients. Stable hemodialysis patients with intact parathyroid hormone ≤240 pg/mL meeting ≥1 of the following criteria (age >65 years, postmenopause, diabetes mellitus) were randomized into the LC and CC groups. LC group patients initially received LC 750 mg/day or the previously used dose and were titrated up to a maximum 2250 mg/day to achieve serum P levels of 3.5–6.0 mg/dL. CC group patients received CC 3 g/day or the previously used dose and were titrated to achieve the same P range. If the target serum P level was not achieved, non-Ca-based P binders (other than LC) could also be added. The primary endpoint is survival time free of cardiovascular events, including cardiovascular death, non-fatal myocardial infarction or stroke, and unstable angina.

Results

Overall, 2309 patients were allocated to the LC (N = 1154) or CC group (N = 1155). At baseline, the mean age was 68.4 years, 40.4 % were women, 55.9 % had diabetes, 18.3 % had a history of ischemic heart disease, and 13.9 % had cerebrovascular disease. A total of 184 patients (8.4 %) had undergone coronary intervention procedures. Baseline characteristics were well balanced between groups.

Conclusions

The LANDMARK study will determine whether LC, a non-Ca-based P binder, reduces cardiovascular mortality and morbidity in chronic hemodialysis patients.

Topical Sodium Thiosulfate: A Treatment for Calcifications in Hyperphosphatemic Familial Tumoral Calcinosis?

CONTEXT

Hyperphosphatemic familial tumoral calcinosis (HFTC) and hyperphosphatemia hyperostosis syndrome (HHS) are rare diseases characterized by hyperphosphatemia and ectopic calcifications or recurrent episodes of diaphysitis. In the setting of metabolic or inflammatory diseases, recent data suggest that systemic administration of sodium thiosulfate (STS) could be effective in the treatment of ectopic calcifications but may also be poorly tolerated (digestive symptoms, metabolic acidosis). Our group developed a topical formulation of STS to treat ectopic calcifications locally, therefore limiting patient exposure to the drug and its adverse effects.

OBJECTIVE

We aimed at describing efficacy and tolerance for a topical formulation of STS in treated patients.

DESIGN

We performed a retrospective study wherein clinical, radiological, and biological data before and after the application of the topical STS treatment were collected and analyzed.

PATIENTS OR OTHER PARTICIPANTS

Three patients admitted to 3 different hospitals with an ectopic calcification secondary to HFTC or HHS were treated with topical STS.

INTERVENTION

The topical STS was applied daily by the patients.

RESULTS

A significant clinical and radiological decrease of ectopic calcifications was observed after at least 5 months of treatment. The STS treatment was well tolerated and no clinical or biological side effects were observed.

CONCLUSION

Topical STS appears to be a promising treatment for ectopic calcifications secondary to HFTC or HHS.

Meal phosphate variability does not support fixed dose phosphate binder schedules for patients treated with peritoneal dialysis: a prospective cohort study

BACKGROUND

Removal of phosphate by peritoneal dialysis is insufficient to maintain normal serum phosphate levels such that most patients must take phosphate binders with their meals. However, phosphate 'counting' is complicated and many patients are simply prescribed a specific dose of phosphate binders with each meal. Therefore, our primary objective was to assess the variability in meal phosphate content to determine the appropriateness of this approach.

METHODS

In this prospective cohort study, adult patients with ESRD treated with peritoneal dialysis and prescribed phosphate binder therapy were eligible to participate. Participants were excluded from the study if they were unable to give consent, had hypercalcemia, were visually or hearing impaired or were expected to receive a renal transplant during the time of the study. After providing informed consent, patients kept a 3-day diet diary that included all foods and beverages consumed in addition to portion sizes. At the same time, patients documented the amount of phosphate binders taken with each meal. The phosphate content of the each meal was estimated using ESHA Food Processor SQL Software by a registered dietitian. Meal phosphate and binder variability were estimated by the Intra Class Correlation Coefficient (ICC) where 0 indicates maximal variability and 1 indicates no variability.

RESULTS

Seventy-eight patients consented to participate in the study; 18 did not complete the study protocol. The patients were 60 (± 17) years, predominately male (38/60) and Caucasian (51/60). Diabetic nephropathy was the most common cause of end stage kidney disease. The daily phosphate intake including snacks ranged from 959 ± 249 to 1144 ± 362 mg. The phosphate ICC by meal: breakfast 0.63, lunch 0.16; supper 0.27. The phosphate binder ICC by meal: breakfast 0.68, lunch 0.73, supper 0.67.

CONCLUSION

The standard prescription of a set number of phosphate binders with each meal is not supported by the data; patients do not appear to be adjusting their binders to match the meal phosphate content. An easy to use phosphate counting program that assists the patient in determining the appropriate amount of phosphate binder to take may enhance phosphate control.

[Phosphorus: a new cardiovascular risk factor?]

Phosphorus is an essential mineral in the regulation of many metabolic processes. However, is known as alterations in serum phosphate levels, compared to the normal range, have clinical relevance: many studies about phosphorus and cardiovascular risk have shown that high serum phosphate levels are associated with clinical and subclinical cardiovascular disease, in CKD and non-CKD patients. In recent years, serum phosphate level within the upper limits of normal range is also identified as a "stealthier killer", and has emerged as a risk factor of cardiovascular mortality and progression of CKD. This mounting evidence suggests the possibility that lowering serum phosphate levels may be a future target of cardiovascular disease management, also through the use of early biomarkers of phosphate overload, such as FGF23, Klotho or the urinary fractional excretion of phosphate. The goal must be an early diagnosis and treatment of disordered phosphorus metabolism, before end-organ damage occurs. Since the western diet is rich in phosphate, a dietary restriction associated with the use of phosphate binders, as well as the use of intervention such as calcitriol supplementation, certainly will have a positive influence on the phosphate-regulatory axis.

Mineral (Mal)Adaptation to Kidney Disease--Young Investigator Award Address: American Society of Nephrology Kidney Week 2014

In the short time since its initial discovery as the cause of rare hypophosphatemic disorders, fibroblast growth factor-23 (FGF-23) has emerged as a major regulator of mineral metabolism and critical component of the bone and mineral adaptation to CKD. However, because elevated FGF-23 levels are also a novel biomarker and possible molecular mediator of increased risks of cardiovascular disease and death in CKD, the initially adaptive response to increase FGF-23 levels to maintain neutral phosphate balance in CKD may ultimately become maladaptive. Incorporating FGF-23 into understanding the complex physiology that governs normal bone and mineral metabolism and its alterations in CKD has filled critical knowledge gaps and opened a new landscape of exciting hypotheses and novel therapeutic strategies to be tested in the continued quest to alleviate the burden of CKD.

Serum phosphorus levels in premature infants receiving a donor human milk derived fortifier

An elevated serum phosphorus (P) has been anecdotally described in premature infants receiving human milk fortified with donor human milk-derived fortifier (HMDF). No studies have prospectively investigated serum P in premature infants receiving this fortification strategy. In this single center prospective observational cohort study, extremely premature infants ≤ 1250 grams (g) birth weight (BW) were fed an exclusive human milk-based diet receiving HMDF and serum P levels were obtained. We evaluated 93 infants with a mean gestational age of 27.5 ± 2.0 weeks (Mean ± SD) and BW of 904 ± 178 g. Seventeen infants (18.3%) had at least one high serum P level with a mean serum P of 9.2 ± 1.1 mg/dL occurring at 19 ± 11 days of life. For all infants, the highest serum P was inversely correlated to the day of life of the infant (p < 0.001, R2 = 0.175) and positively correlated with energy density of HMDF (p = 0.035). Serum P was not significantly related to gender, BW, gestational age, or days to full feeds. We conclude that the incidence of hyperphosphatemia was mild and transient in this population. The risk decreased with infant age and was unrelated to gender, BW, or ethnicity.

A Practical Clinical Approach to Paediatric Phosphate Disorders

Phosphate metabolism is critical to multiple systems and cellular functions. Disruption of any point in the pathways of phosphate metabolism may cause serum phosphate abnormalities and resultant acute or chronic clinical conditions. The study of phosphate disorders has revealed a wealth of information regarding normal phosphate physiology. Careful evaluation of affected patients based on pathophysiologic assessments will usually identify the aetiology of hypophosphataemia or hyperphosphataemia, which is important to guide appropriate therapy. Because of the relative importance of chronic hypophosphataemia and hyperphosphataemia to bone disease, much of this chapter will focus on chronic disorders, especially those mediated by excess or deficient fibroblast growth factor 23 functioning.

[Phosphate disorders: hyperphosphatemia or pseudohyperphosphatemia?]

We report the case of a 79 year old woman presenting with progressive confusion and drowsiness. Renal insufficiency with hyperkalemia as well as hypercalcemia and severe hyperphosphatemia were diagnosed. Renal insufficiency improved with treatment. However, hyperphosphatemia persisted without apparent explanation. We discuss possible causes of hyper- and pseudohyperphosphatemia. Specifically, phosphate analysis may be disturbed by the paraproteins in patients with multiple myeloma, resulting in pseudohyperphosphatemia. We review the standard laboratory phosphate measurement and the mechanisms of interference with paraproteins.

Lanthanum carbonate versus placebo for management of hyperphosphatemia in patients undergoing peritoneal dialysis: a subgroup analysis of a phase 2 randomized controlled study of dialysis patients

BACKGROUND

This short-term study assessed the efficacy and safety of lanthanum carbonate in the treatment of hyperphosphatemia in dialysis patients; here, we report a prespecified subgroup analysis of patients undergoing peritoneal dialysis.

METHODS

Men and women (n=39) who had received continuous ambulatory peritoneal dialysis for chronic kidney disease for 6 months or more were enrolled in eight renal medicine departments in the United Kingdom. A 2-week washout period was followed by a 4-week dose-titration phase during which patients received lanthanum carbonate titrated up to 2250 mg/day. This was followed by a 4-week, randomized, placebo-controlled, parallel-group phase during which patients continued to receive either lanthanum carbonate at the titrated dose, or a matched dose of placebo. The main outcome measure was control of serum phosphate levels (1.3-1.8 mmol/l) at the end of the parallel-group phase.

RESULTS

Serum phosphate was controlled in 3/39 (8%) patients at the beginning of the dose-titration phase (after washout) and in 18/31 (58%) patients treated with lanthanum carbonate at its end. After the parallel-group phase, 60% of lanthanum carbonate-treated patients and 10% of those receiving placebo had controlled serum phosphate. There was no difference in mean (95% confidence interval) serum phosphate levels between groups at randomization: lanthanum carbonate, 1.57 (1.34-1.81) mmol/l; placebo, 1.58 (1.40-1.76) mmol/l (p=0.96). However, a difference was seen at the end of the parallel-group phase: lanthanum carbonate, 1.56 (1.33-1.79) mmol/l; placebo, 2.25 (1.81-2.68) mmol/l (p=0.0015). There were no clinically important changes in nutritional parameters and no serious treatment-related adverse events were recorded.

CONCLUSIONS

At doses up to 2250 mg/day, lanthanum carbonate is well tolerated and controls hyperphosphatemia effectively. Treatment with higher doses of lanthanum carbonate may allow patients undergoing peritoneal dialysis the potential to increase their dietary protein intake without compromising their phosphate control.

Mineral and bone disorder in Chinese dialysis patients: a multicenter study

BACKGROUND

Mineral and bone disorder (MBD) in patients with chronic kidney disease is associated with increased morbidity and mortality. Studies regarding the status of MBD treatment in developing countries, especially in Chinese dialysis patients are extremely limited.

METHODS

A cross-sectional study of 1711 haemodialysis (HD) patients and 363 peritoneal dialysis (PD) patients were enrolled. Parameters related to MBD, including serum phosphorus (P), calcium (Ca), intact parathyroid hormone (iPTH) were analyzed. The achievement of MBD targets was compared with the results from the Dialysis Outcomes and Practice Study (DOPPS) 3 and DOPPS 4. Factors associated with hyperphosphatemia were examined.

RESULTS

Total 2074 dialysis patients from 28 hospitals were involved in this study. Only 38.5%, 39.6% and 26.6% of them met the Kidney Disease Outcomes Quality Initiative (K/DOQI) defined targets for serum P, Ca and iPTH levels. Serum P and Ca levels were statistically higher (P < 0.05) in the HD patients compared with those of PD patients, which was (6.3 ± 2.1) mg/dL vs (5.7 ± 2.0) mg/dL and (9.3 ± 1.1) mg/dL vs (9.2 ± 1.1) mg/dL, respectively. Serum iPTH level were statistically higher in the PD patients compared with those of HD patients (P = 0.03). The percentage of patients reached the K/DOQI targets for P (37.6% vs 49.8% vs 54.5%, P < 0.01), Ca (38.6% vs 50.4% vs 56.0%, P < 0.01) and iPTH (26.5% vs 31.4% vs 32.1%, P < 0.01) were lower among HD patients, compared with the data from DOPPS 3 and DOPPS 4. The percentage of patients with serum phosphorus level above 5.5 mg/dL was 57.4% in HD patients and 47.4% in PD patients. Age, dialysis patterns and region of residency were independently associated with hyperphosphatemia.

CONCLUSIONS

Status of MBD is sub-optimal among Chinese patients receiving dialysis. The issue of hyperphosphatemia is prominent and needs further attention.

Vascular calcifications in chronic kidney disease--clinical management

Chronic kidney disease (CKD) patients could present various types of calcifications causing different pathological conditions that would contribute to the renal disease progression and high risk of mortality. Extra-skeletal calcifications represent a common consequence of mineral bone disorders in CKD patients. Vascular calcifications represent a complex systemic manifestation caused by phospho-calcium homeostasis disorders, by imbalance among promoters and inhibitors of calcification and the presence of various arterial diseases and other risk factors. Consequently, vascular calcification can be considered an active pathological process that resembles osteogenesis. Therefore, before starting a suitable therapy for the prevention or delay of vascular calcifications, our recommendations are: to perform lateral abdominal radiography or CT-based techniques in CKD stages 3-5 patients for an early vascular calcification detection, to assess thoroughly patients presenting hyperphosphatemia, hyperparathyroidism, vitamin D deficiency and to understand clearly the pathophysiology of arterial calcification and calciphylaxis.

Hyperphosphatasemia in an adult. Clinical, conventional roentgenographic, and CT findings

A 47-year-old Saudi deaf lady with short stature presented being unable to walk. She had long standing diffuse skeletal deformities, and progressive head enlargement. She had markedly elevated serum alkaline phosphatase. The radiographic changes were those of hyperphosphatasemia, and the CT scanning of the skull, which was not studied before, further elicited the extensive calvarial and basilar changes. The various entities of hyperphosphatasemia with and without bony changes are reviewed.

[Fibroblast growth factor 23--a phosphate regulating hormone]

Fibroblast growth factor 23 (FGF23) is a recently identified phosphatonin. Its main physiological functions are to maintain serum phosphate within its reference range and to counter regulate the effects of vitamin D. Diseases correlated to high serum values of FGF23 are hypophosphatemic rickets, fibrous dysplasia, and tumour-induced osteomalacia. In contrast, hyperphosphatemic tumoral calcinosis is associated with accelerated degradation of FGF23. Measuring FGF23 serves as a differential diagnostic tool in elucidating conditions of long-lasting hypophosphatemia.

[Clinical aspect of recent progress in phosphate metabolism. Clinical usefulness of measurement of fibroblast growth factor 23 (FGF23)]

Through the studies of patients with hypophosphatemic rickets/osteomalacia, FGF23 has emerged as a humoral factor that reduces serum phosphate. Discovery of FGF23 as an essential regulator of phosphate homeostasis has markedly improved our understanding of phosphate homeostasis and hypophosphatemic or hyperphosphatemic disorders. Measurement of circulatory FGF23 levels seems to be useful for diagnosis of these disorder. Novel therapeutic methods for these disorder may be developed by elucidation of the mechanism of action of FGF23.

[Clinical aspect of recent progress in phosphate metabolism. Hyperphosphatemia and hypophosphatemia]

Serum inorganic phosphate (Pi) concentrations are generally maintained at 2.5-4.5 mg/dL in adults. In children, serum Pi levels are higher than those in adults. Hyperphosphatemia may be the consequence of (1) a decreased excretion of Pi, or (2) an external or internal cause of acute Pi loading to extracellular fluid, and the chronic kidney disease (CKD) is the most frequent cause of hyperphosphatemia. Hyperphosphatemia due to the increased Pi reabsorption is associated with hyperparathyroidism, tumoral calcinosis, and so on. Hypophosphatemia may be caused by (1) a decreased Pi intake, (2) an increased excretion of Pi, or (3) the transcellular shift of Pi from the extracellular to the intracellular space. Hypophosphatemia due to the increased excretion of Pi can be observed in various diseases, including Fanconi syndrome, hereditary hypophosphatemic rickets/osteomalacia, and tumor-induced hypophosphatemic osteomalacia.

Newly discovered mutations in the GALNT3 gene causing autosomal recessive hyperostosis-hyperphosphatemia syndrome

BACKGROUND AND PURPOSE

Periosteal new bone formation and cortical hyperostosis often suggest an initial diagnosis of bone malignancy or osteomyelitis. In the present study, we investigated the cause of persistent bone hyperostosis in the offspring of two consanguineous parents.

METHODS

Clinical assessment, imaging, and direct sequencing were used to elucidate the etiology of the condition seen in the patient.

RESULTS

Radiological examination revealed periosteal reaction, diaphysitis, and cortical hyperostosis, suggesting osteomyelitis or a bone neoplasm. The clinical and radiological features were also reminiscent of hyperostosis with hyperphosphatemia (HHS), a rare autosomal recessive disease manifesting with recurrent, transient, and painful swelling of the long bones. The identification of two novel heterozygous pathogenic mutations in the GALNT3 gene confirmed a diagnosis of HHS.

INTERPRETATION

Molecular analysis represents an invaluable tool in the differential diagnosis of persistent cortical hyperostosis.

Disorders of phosphate homeostasis and tissue mineralisation

Phosphate is absorbed from the diet in the gut, stored as hydroxyapatite in the skeleton, and excreted with the urine. The balance between these compartments determines the circulating phosphate concentration. Fibroblast growth factor 23 (FGF23) has recently been discovered and is part of a previously unrecognised hormonal bone-kidney axis. Phosphate-regulating gene with homologies to endopeptidases on the X chromosome, and dentin matrix protein 1 regulate the expression of FGF23 in osteocytes, which then is O-glycosylated by UDP-N-acetyl-alpha-D-galactosamine: polypeptide N-acetylgalactosaminyl-transferase 3 and secreted into the circulation. FGF23 binds with high affinity to fibroblast growth factor receptor 1c in the presence of its co-receptor Klotho. It inhibits, either directly or indirectly, reabsorption of phosphate and the synthesis of 1,25-dihydroxy-vitamin-D by the renal proximal tubule and the secretion of parathyroid hormone by the parathyroid glands. Acquired or inborn errors affecting this newly discovered hormonal system can lead to abnormal phosphate homeostasis and/or tissue mineralisation. This chapter will provide an update on the current knowledge of the pathophysiology, the clinical presentation, diagnostic evaluation and therapy of the disorders of phosphate homeostasis and tissue mineralisation.

Hyperostosis and hyperphosphataemia syndrome: a diagnostic dilemma

The syndrome of hyperostosis and hyperphosphataemia (HHS) is very rare. It can mimic bone infections and tumours. A nine-year-old girl presented with pain in her left lower leg. Radiographs showed patchy sclerosis in the tibial diaphysis. Investigations were normal except for hyperphosphataemia. Open biopsy showed chronic inflammation. Bacterial cultures were negative. Four months later, she had pain in the other leg. On evaluation for hyperphosphataemia, there was increased renal reabsorption of phosphates. She responded to analgesics. In patients between six and 16 years of age, HHS must be considered when there is painful diaphyseal swelling of long bones associated with isolated hyperphosphataemia. The painful episodes can recur. Surgical decompression can be considered if conservative treatment methods are ineffective.

Transient hyperphosphatasemia in an infant with bronchiolitis and pneumonia

We present a case of benign transient hyperphosphatasemia in a 4-month-old infant with acute bronchiolitis and pneumonia. During hospitalization the infant had an increased catalytic activity of alkaline phosphatase (ALP): day 2, 5074 U/L; day 3, 5622-U/L; and day 8, 3129 U/L. The x-ray, leukocytosis, and C-reactive protein findings pointed to bacterial etiology of the respiratory disorder. Electrophoretic separation revealed an atypical isoenzyme profile: fast anodal, near-cathodal and bone fractions. ALP levels normalized within 54 days, and control electrophoresis indicated normal liver, placental/placental-like, intestinal and bone isoenzymes. The appearance of atypical fast anodal and near-cathodal fractions of ALP in this infant during the course of acute lower respiratory tract infection and rapid return to the reference intervals pointed to benign transient hyperphosphatasemia.

Asymptomatic disseminated carcinomatosis of bone marrow presenting as hyperphosphatasia: report of a case

Metastatic involvement of the musculoskeletal system is one of the most significant clinical issues facing orthopaedic oncologists. The number of patients with metastasis to the skeletal system from a carcinoma is 15 times greater than the number of patients with primary bone tumours of all types. However, progression patterns like disseminated carcinomatosis of bone marrow are comparatively rare. The pathophysiology for disseminated carcinomatosis of bone marrow, with a prognosis reported to be very poor, is still unknown. We describe a patient who had no symptoms with hyperphosphatasia. Bone scintigraphy showed a so-called super bone scan and a needle biopsy from the ileum showed adenocarcinoma cells. Additional endoscopic investigation was performed and signet cell gastric cancer was found. From the bone scan and biopsy, we established the diagnosis of disseminated carcinomatosis of the bone marrow. From the experience of this case, we believe that intensive stomach investigation should be considered in cases with hyperphosphatasia, even when the patient has no symptoms.

Extreme hyperphosphatemia and hypocalcemic coma associated with phosphate enema

Fleet enema (sodium phosphate, C.B. Fleet Co., Inc., Lynchburg, Virginia) is widely used for bowel preparation or constipation relief in the hospital and over the counter. The potential risks, including hyperphosphatemia and hypocalcemic coma should be kept in mind of primary care physician. The patients with older age, bowel obstruction, small intestinal disorders, poor gut motility, and renal disease are contraindicated or should be administered with caution. We present a patient with old age and chronic renal failure who developed severe hyperphosphatemia and hypocalcemic tetany with coma after sodium phosphate enema. We recommend the use of alternative enema preparations, such as simple tap water or saline solution enemas, which can prevent fatal complications in high risk patients.

A new approach to the evaluation of hyperphosphatemia in chronic kidney disease

AIMS

Hyperphosphoremia, main contributor to cardiovascular calcifications, has a major impact on the morbidity and mortality of chronic renal failure (CRF) patients. Phosphate binders and dietary phosphate limitation are not effective enough to abolish hyperphosphoremia-induced cardiovascular abnormalities, therefore, the identification of other and more timely approaches for serum phosphorous reduction is necessary. Salivary fluid contains phosphate which, if related to the daily salivary secretion (1,000 - 1,800 ml), deserves attention as a marker for an earlier start of pharmacologic treatment for phosphorous removal. In ESRD patients under dialysis we have shown increased salivary phosphate closely to be related with serum phosphorous and interpreted as compensatory. This study evaluates salivary phosphate secretion in 77 nondialyzed CRF compared with healthy subjects and its relationship with renal function.

METHODS

Saxon's test confirmed normal salivary function in patients and controls. Serum phosphorous, creatinine and GFR were also measured.

RESULTS

Salivary phosphorous was significantly higher in CRF patients compared with controls: 38.60 mg/dl (range 12.20 - 95.60) vs 16.30 (10.30 - 27.10), p < 0.0001; serum phosphate was also significantly higher: 3.70 (2.10 - 6.80) vs 3.50 (2.3 4.6), p = 0.013. In CRF patients, salivary phosphorous positively correlated with serum phosphorous (r - 0.45, p < 0.0001) and with serum creatinine (r = 0.72, p < 0.0001), while negatively correlated with GFR (r = -0.72, p < 0.0001).

CONCLUSIONS

The results of our study show also in CRF patients increased salivary phosphate secretion, which is related with renal function. On this basis the use of salivary phosphate secretion as a marker for an earlier start of the abnormal phosphate, metabolism pharmacologic treatment could be proposed.