Serum cystatin C in pregnant women: reference values, reliable and superior diagnostic accuracy

BACKGROUND

A simple, endogenous, accurate and minimally invasive marker of glomerular filtration rate (GFR) is much desired in clinical nephrology. Cystatin C fulfills all criteria to be a marker for GFR. For early detection of renal impairment in pregnant women, it is necessary to determine serum cystatin C reference values and the correlation with GFR. The present study was therefore undertaken.

METHOD

Healthy pregnant women were followed during pregnancy and the postnatal period. Patient demographics included age, height, weight, BMI, parity, total blood count, LFT, urea, creatinine, Na, K, and blood sugar. Serum cystatin C was estimated using particle enhanced nephlo-immunoassay method. All the parameters were recorded at the start of pregnancy and then in each trimester and the postnatal period. Regression analysis correlation coefficient, ANOVA and the Student's t-test were used for analysis using the SPSS statistical package.

RESULTS

A total of 197 pregnant women were included. Mean serum cystatin C for all the women was 0.82 +/- 0.184 mg/l. Serum cystatin C levels were high -0.89 +/- 0.12 mg/l in the first trimester, decreased significantly to 0.651 +/- 0.14 mg/l during the second trimester (p = 0.0000 compared to first trimester), and increased again to 0.82 +/- 0.191 mg/l in the third trimester. After delivery the level rose to 0.94 +/- 0.12 mg/l. A strong correlation was found between serum cystatin C and serum creatinine. A strong negative correlation was found between GFR and cystatin C values in the women (r = -0.546, p = 0.000). A linear relationship was found between GFR and cystatin C levels. A significant increase in the GFR was noted with the progression of pregnancy from 128.06 +/- 29.7 ml/min in the first trimester to 155.2 +/- 29.59 ml/min during second trimester (p = 0.006). A decline in the level of cystatin C exactly parallel to the increase in the GFR was noted with the progression of pregnancy. Interestingly cystatin C was found to have a strong negative correlation with gestational age (r = -0.663, p = 0.000).

CONCLUSION

Our results indicate that the mean serum cystatin C levels reflect changes in the GFR during the entire pregnancy and also in the postnatal period. Moreover, serum cystatin C levels are independent of age, height, weight, or blood sugar level. Cystatin C can be used for close supervision and early diagnosis of renal impairment in pregnant patients. Cystatin C is a reliable, useful and promising marker of GFR in pregnant women.

Pharmacokinetics and Pharmacodynamics of Febuxostat, a New Non-purine Selective Inhibitor of Xanthine Oxidase in Subjects with Renal Impairment

To assess the safety, pharmacokinetics, and pharmacodynamics of febuxostat in subjects with normal renal function or renal impairment, febuxostat (80 mg/d) was orally administered for 7 days to subjects with normal renal function (n = 11, CLcr >80 mL/min/1.73 m) or to subjects with mild (n = 6, CLcr 50-80 mL/min/1.73 m), moderate (n = 7, CLcr 30-49 mL/min/1.73 m), or severe renal impairment (n = 7, CLcr 10-29 mL/min/1.73 m). The pharmacokinetics of febuxostat and its active quantifiable metabolites 67M-1, 67M-2, and 67M-4 as well as the pharmacodynamics of uric acid, xanthine, and hypoxanthine were determined in plasma (or serum) and urine. Febuxostat was safe and well tolerated. Regression analyses indicated that febuxostat tmax and Cmax,u values were not affected by CLcr. However, for AUC24,u, CLu/F, and t1/2z, regression analyses indicated a statistically significant relationship with CLcr. With the exception of 67M-1 Cmax, regression analyses for 67M-2 and 67M-4 Cmax, and for AUC24 for all 3 metabolites indicated a statistically significant linear relationship with CLcr. Irrespective of renal function group, the mean serum uric acid concentrations decreased by 55% to 64% by day 7. Although plasma exposure to febuxostat and its metabolites was generally higher in subjects with increasing degrees of renal impairment, the percentages of decrease in serum uric acid were comparable regardless of the renal function group. A once-daily 80-mg dose of febuxostat appears to be safe and well tolerated in different renal function groups and does not appear to require any dose adjustment based on differences in renal function.

Evolution of the parathyroid hormone (PTH) assay--importance of circulating PTH immunoheterogeneity and of its regulation

Most of what we know on PTH bioactivity has been associated with the first 34 amino acids of the PTH structure acting on the type I PTH/PTHrP receptor, leaving little place to the carboxyl-terminal structure. This reality has dictated the evolution of the PTH assay. The first generation of PTH assays has permitted the description of circulating PTH immunoreactivity and of its acute regulation by calcium concentration. Most assays reacted with the dominant forms of circulating PTH, PTH fragments devoid of bioactivity. This was believed to limit their clinical performance, particularly in the diagnosis of hypercalcemic disorders and the evaluation of secondary hyperparathyroidism and/or bone diseases associated with chronic renal failure. This brought up the development of a 2nd generation of PTH assays, the Intact (I) PTH assay. These assays were initially demonstrated to react only with hPTH(1-84), the bioactive form of the hormone. They greatly improved the differential diagnosis of hypercalcemic disorders, facilitated studies of parathyroid function in renal failure patients but were still limited in their capacity to dissociate the various bone diseases associated with chronic renal failure. Eventually, it was demonstrated that these assays, which used 13-34 epitopes, reacted with large C-PTH fragments having a partially preserved amino-terminal (N) structure, also called non-(1-84) PTH. These fragments accounted for up to 50% of I-PTH immunoreactivity in renal failure patients. hPTH(7-84), a surrogate of non-(1-84) PTH fragments, was demonstrated to cause hypocalcemia and to antagonize hPTH(1-34) and hPTH(1-84) calcemic effect in vivo and to inhibit bone resorption in vitro via a C-PTH receptor, different from the type I PTH/PTHrP receptor. This suggested a dual control of calcium concentration via N- and C-PTH molecular forms. This also explained why the ratio of C-PTH fragments/I-PTH was so well regulated both acutely and chronically in various experimental conditions. The fact that I-PTH assays detected circulating PTH molecular forms with biological effects opposite to those of hPTH(1-84) was believed to explain their limitations, particularly in renal failure, and prompted the evolution of a third generation of PTH assays. The last is based on a 1-4 epitope to reveal PTH(1-84) and not hPTH(7-84). It also permits an indirect evaluation of non-(1-84) PTH fragments by subtracting a 3rd generation PTH value from a 2nd generation PTH value and the calculation of a PTH(1-84)/non-(1-84) PTH ratio. The combination of a third generation PTH value with the PTH(1-84)/non-(1-84) PTH ratio value has in some studies improved the differential diagnosis of bone diseases associated with renal failure. But more studies are required to see whether PTH(1-84)/PTH fragment ratios will improve the clinical performance of PTH concentrations used alone.

The effects of age and hyperhomocysteinemia on the redox forms of plasma thiols

We assayed the redox forms of cysteine (reduced [CSH], oxidized [CSSC], and bound to protein [CS-SP]), cysteinylglycine (CGSH; cysteinylgycine disulfide [CGSSGC] and cysteinylglycine-protein mixed disulfide [CGS-SP]), glutathione (GSH; glutathione disulfide [GSSG] and glutathione-protein mixed disulfide [GS-SP]), homocysteine (Hcy; homocystine [HcyS] and homocystine-protein mixed disulfides [bHcy]), and protein sulfhydryls in the plasma of healthy subjects (divided into 8 groups ranging in age from birth to 70 years) and patients with mild hyperhomocysteinemia associated with cardiovascular disease (heart-transplant patients) or vascular atherosclerosis, with or without renal failure. In healthy individuals, levels of disulfides and protein-mixed disulfides were more abundant than those of thiols, and those of protein-thiol mixed disulfides were higher than disulfides. Concentrations of CSH, GSH, and CGSH in the various groups had profiles characterized by a maximum over time. The concentration of Hcy was unchanged up to the age of 30 years, after which it increased. CSSC concentration increased gradually with age, whereas concentrations of the other disulfides were essentially unchanged. By contrast, the concentrations of all protein-thiol mixed disulfides, especially those with CSH, increased gradually with age. Ranks of distribution of the reduced forms changed with age (at birth, CSH > CGSH > GSH > Hcy; in 1- to 2-year-olds, CSH > GSH > CGSH > Hcy; and in 51- to 70-year-olds, CSH > CGSH = GSH > Hcy), whereas those of disulfides and protein-thiol mixed disulfides were substantially unchanged (in all age groups, CSSC > CGSSGC > GSSG = HcyS and CS-SP > CGS-SP > bHcy > GS-SP). In patients with pathologic conditions, plasma levels of disulfide forms CSSC, HcyS, CS-SP, and bHcy were significantly increased, whereas other redox forms of thiols were unchanged or showed variations opposite (increasing or decreasing) to control values. Maximal increases in disulfides and protein-thiol mixed disulfides were associated with renal failure. Our data suggest that increases in plasma bHcy concentrations in subjects with pathologic conditions were more likely the result of activation of thiol-disulfide exchange reactions between free reduced Hcy and CS-SP than of a direct action of reactive oxygen species.

Monitoring haemodialysis using electronic nose and chemometrics

An ever-increasing number of patients have to undergo regular renal dialysis to compensate for acute or chronic renal failure. The adequacy of the treatment has a profound effect on patients' morbidity and mortality. Therefore, it is necessary to assess the delivered dialysis dose. For the quantification of the dialysis dose, two parameters are most commonly used, namely the K(t)/V value (normalised dose of dialysis) and the urea reduction rate, yet the prescribed dialysis dose often differs from the actual delivered dialysis dose. Currently, no interactive process is available to ensure optimal treatment. The aim of this study was to investigate the potential for an "electronic nose" as a novel monitoring tool for haemodialysis. Blood samples were analysed using an electronic nose, comprising an array of 14 conducting polymer sensors, and compared to traditional biochemistry. Principal component analysis and hierarchical cluster analysis were applied to evaluate the data, and demonstrated the ability to distinguish between pre-dialysis blood from post-dialysis blood independent of the method used. It is concluded that the electronic nose is capable of discriminating pre-dialysis from post-dialysis blood and hence, together with an appropriate classification model, suitable for on-line monitoring.

[Value of troponins in acute coronary syndrome in patients with renal failure]

Patients with renal insufficiency can have elevations of serum troponin without suspected clinical coronary ischemia. Although cardiovascular disease is the main cause of death in patients with renal failure, the process of elevation of serum troponin is not well known. Troponin T is more frequently elevated than troponin I in these patients which leads to uncertainty in the clinical interpretation of results. There are studies suggesting that troponin elevations are associated with a higher risk and increased mortality. To explain the process leading to troponin increases in this kind of pathology and to confirm its usefulness in the diagnosis, evolution and prognosis it would be necessary to carry out more clinical studies monitoring troponin and studying the stratification of risk.

Clinical Association between Renal Insufficiency and Positive Troponin I in Patients with Acute Coronary Syndrome

BACKGROUND

Whether renal insufficiency (RI) influences troponin levels in patients with acute coronary syndromes (ACS) is controversial. We attempted to determine whether there is an association between RI and troponin I (TnI) elevation in patients presenting with ACS.

METHODS

We studied 764 consecutive patients with ACS admitted to our institution from January 1999 to June 2000. Patients were identified prospectively and data were collected through chart review of all cases with an admission diagnosis of ACS. In order to assess the relationship of TnI and RI, we calculated the creatinine clearance (Cr-Cl) for all patients. We conducted an analysis of variance comparing TnI in quintiles of patients with lowest to highest Cr-Cl.

RESULTS

Among 764 patients, 173 patients had a discharge diagnosis of ST elevation myocardial infarction and 591 had non-ST elevation myocardial infarction. There was no correlation between peak TnI levels and renal function as measured by Cr-Cl in the entire cohort with ACS and in the subgroups with ST elevation myocardial infarction and non ST elevation myocardial infarction.

CONCLUSIONS

This large cohort study demonstrates that there appears to be no association between RI and positive TnI in patients with ACS.

Effect of elevated admission serum creatinine and its worsening on outcome in hospitalized patients with decompensated heart failure

Renal insufficiency (RI), as represented by elevated serum creatinine (>1.5 mg/dl) on admission, is common and found in almost half of patients hospitalized with decompensated heart failure. This finding is associated with prolongation of length of stay and rate of rehospitalizations after discharge and also has an independent unfavorable effect on 6-month mortality. Similarly, an increase in serum creatinine (>0.5 mg/dl) in the hospital results in a significantly longer length of stay and has an independent effect on long-term mortality.

Prediction of glomerular filtration rate from body cell mass and plasma creatinine

The gold standards for the measurement of glomerular filtration rate (GFR) are inulin clearance and radioisotopic methods. However, creatinine clearance is the most used test to evaluate GFR in clinical practice. Its adequacy is questionable, since its repeatability is quite poor, mainly due to errors in the collection of urine. The aim of this study was to evaluate a new method to predict GFR from the body cell mass (BCM) and plasma creatinine (Pcr), avoiding urine collection. The values of BCM were obtained in 275 adult renal patients with different renal function, ranging from normality to advanced renal failure. The relationship of GFR (clearance of (99m)Tc-DTPA) with BCM and Pcr was calculated in the first 85 patients. A highly significant linear correlation was found between GFR and the ratio BCM/Pcr. Thereafter, GFR was predicted from BCM and Pcr (BCM GFR) with formulas derived from the relationships found between GFR and the ratio BCM/Pcr. For comparison, GFR was predicted also according to other prediction formulas: Cockcroft and Gault (CG GFR), and the simplified MDRD formula (MDRD GFR). BCM GFR gave a more precise estimate of GFR than CG GFR and MDRD GFR. In fact, BCM GFR had the best correlation and agreement with true GFR ((99m)Tc-DTPA). Furthermore, CG GFR and MDRD GFR markedly overestimated true GFR. Finally, the error of prediction of BCM GFR was definitely lower than that of the two other estimates of GFR. GFR can be predicted from BCM and plasma creatinine. This method, which is very simple and accurate, seems suitable to establish the adequate dosage of drugs cleared by the kidneys.

Biochemical and spectrophotometric significance of advanced oxidized protein products

We previously described the presence of advanced oxidation protein products (AOPP), a novel marker of oxidative stress in the plasma of hemodialyzed patients (HD). The present study was carried out to further investigate how myeloperoxidase (MPO)-catalyzed reactions could contribute to AOPP generation in the plasma. First, patterns of plasma protein oxidation obtained after in vitro incubation of control plasma with hypochlorous acid (HOCl) were compared to those from HD patients and control plasma. The use of various analytical techniques enabled localising and identifying the main oxidized proteins with albumin (HSA) after protein separation by size-exclusion chromatography and SDS-PAGE electrophoresis. The characterization of the oxidation level of the individual plasma proteins in terms of carbonyl groups and 3-nitrotyrosine formations was performed by immunoblotting. Secondly, to highlight the significance of AOPP index monitored by spectrophotometry, spectra were established for plasma fractions from HD patients and compared to data for control plasma and HOCl-treated plasma. The corresponding absorbance difference spectra were matched with external standards such as dityrosine, nitrotyrosine and pentosidine and elaborated chromophoric probe models. Indeed, HSA was chlorinated by HOCl reagent or HOCl generated via the MPO/H(2)O(2)/Cl(-) system and was nitrated by tetranitromethane. Increased absorbances at the range of 340 nm were observed both with chlorinated and nitrated HSA. Finally, our results indicate that HOCl, and not NO(2)(*), generated via MPO activity, could represent one of the pathways for AOPP production in plasma proteins exposed to activated phagocytes.

Circulating concentration of FGF-23 increases as renal function declines in patients with chronic kidney disease, but does not change in response to variation in phosphate intake in healthy volunteers

BACKGROUND

Hyperphosphatemia is a risk factor for the development of several different complications of chronic kidney disease (CKD), including secondary hyperparathyroidism and cardiovascular complications, due to the formation of calcium-phosphate deposits. Fibroblast growth factor-23 (FGF-23) is a recently discovered protein that is mutated in autosomal-dominant hypophosphatemic rickets, an inherited phosphate wasting disorder, and it may represent a novel hormonal regulator of phosphate homeostasis. We therefore hypothesized that FGF-23 levels may be altered in hyperphosphatemia associated with renal failure and that its concentration changes in response to different levels of phosphate intake.

METHODS

Using a two-site enzyme-linked immunosorbent assay (ELISA) detecting the C-terminal portion of FGF-23, serum concentration was measured in 20 patients with different stages of renal failure (creatinine range 155 to 724 micromol/L), in 33 patients with end-stage renal disease (ESRD) on dialysis treatment, and in 30 patients with functioning renal grafts. Furthermore, six healthy males were given oral phosphate binders in combination with low dietary phosphate intake for 2 days followed by 3 days of repletion with inorganic phosphate. FGF-23 levels were determined at multiple time points.

RESULTS

FGF-23 serum levels were significantly elevated in CKD with a strong correlation between serum creatinine and FGF-23 concentration. Independent correlations were also seen between FGF-23 and phosphate, calcium, parathyroid hormone (PTH), and 1,25(OH)2D3. No changes in serum FGF-23 levels were observed in volunteers following ingestion of oral phosphate binders/low dietary phosphate intake, which led to a decline in phosphate excretion or during the subsequent repletion with inorganic phosphate through oral phosphate and a normal diet.

CONCLUSION

Circulating FGF-23 was significantly elevated in patients with CKD and its concentration correlated with renal creatinine clearance. In healthy volunteers, FGF-23 levels did not change after phosphate deprivation or phosphate loading.

Increased Levels of Pregnancy-Associated Plasma Protein A Are Associated with Mortality in Hemodialysis Patients: Preliminary Results

Pregnancy-associated plasma protein A (PAPP-A) is a new prognostic indicator of acute coronary syndrome. This protein is elevated in hemodialysis (HD) patients and is closely related to inflammation and oxidative stress. The aim of our pilot study was to find out whether PAPP-A is related to mortality in HD patients. 40 HD patients in a stable clinical state (20 men and 20 women, mean age 69 +/- 12 years) were enrolled in the study and followed up for 20 months. PAPP-A was assessed immunochemically (TRACE method) in serum samples (before the HD session) at the beginning of the observation period. During the follow-up, 22 patients died, 15 of them due to cardiovascular events. PAPP-A levels were significantly higher in the patients who died, compared to living HD patients: 26.8 (21.6-36.8) vs. 20 (14.9-26.6) mU/l, p = 0.034. PAPP-A could also be a new prognostic marker in hemodialysis patients, probably due to its close association with cardiovascular risk. More extensive studies are required to confirm this hypothesis.

Fibroblast growth factor (FGF)-23 in patients with primary hyperparathyroidism

OBJECTIVE

We aimed to determine the serum level of fibroblast growth factor-23 (FGF-23) in patients with primary hyperparathyroidism (pHPT) to understand its physiological role in the disorder.

PATIENTS AND METHODS

Ninety-eight patients with pHPT who underwent parathyroidectomy formed the study group. We also measured serum FGF-23 in 11 of these patients on postoperative day 6.

RESULTS

Serum FGF-23 levels was significantly higher in pHPT patients than in healthy controls (35.6+/-17.8 ng/l vs 28.9+/-11.2 ng/l (mean+/-s.d.); P<0.001 (Pearson's correlation coefficient)), but there was no significant difference in the serum FGF-23 level between pHPT patients with normal renal function (creatinine clearance (Ccr) of >or=70 ml/min) and healthy controls. Serum FGF-23 correlated positively with serum calcium (P<0.0001) and intact parathyroid hormone (PTH) (P<0.01), and negatively with Ccr (P<0.001), serum phosphate (P<0.05), and serum 1,25-dihydroxyvitamin D (1,25(OH)(2)D) (P<0.05). Multiple linear regression analysis of factors potentially determining serum FGF-23 levels in pHPT patients showed serum calcium (P<0.01) and Ccr (P<0.001) to be significant predictors. The serum levels of FGF-23 did not change after parathyroidectomy despite the normalization of serum calcium values. Multiple linear regression analysis revealed that serum FGF-23 was not a significant predictor of serum phosphate or 1,25(OH)(2)D in pHPT patients.

CONCLUSIONS

FGF-23 may not play a significant role in regulating phosphate or 1,25(OH)(2)D in pHPT patients, especially in those with normal renal function. Further studies are warranted to determine the role of FGF-23 in renal insufficiency or failure.

Measurement of Nε-(Carboxymethyl)lysine and Nε-(Carboxyethyl)lysine in Human Plasma Protein by Stable-Isotope-Dilution Tandem Mass Spectrometry

Background: N ε-(Carboxymethyl)lysine (CML) and Nε-(carboxyethyl)lysine (CEL) are two stable, nonenzymatic chemical modifications of protein lysine residues resulting from glycation and oxidation reactions. We developed a tandem mass spectrometric method for their simultaneous measurement in hydrolysates of plasma proteins.

Methods: CML and CEL were liberated from plasma proteins by acid hydrolysis after addition of deuterated CML and CEL as internal standards. Chromatographic separation was performed by gradient-elution reversed-phase chromatography with a mobile phase containing 5 mmol/L nonafluoropentanoic acid as ion-pairing agent. Mass transitions of 205.1→84.1 and 219.1→84.1 for CML and CEL, respectively, and 209.1→88.1 and 223.1→88.1 for their respective internal standards were monitored in positive-ion mode.

Results: CML and CEL were separated with baseline resolution with a total analysis time of 21 min. The lower limit of quantification was 0.02 μmol/L for both compounds. Mean recoveries from plasma samples to which CML and CEL had been added were 92% for CML and 98% for CEL. Within-day CVs were &lt;7.2% for CML and &lt;8.2% for CEL, and between-day CVs were &lt;8.5% for CML and &lt;9.0% for CEL. In healthy individuals (n = 10), mean (SD) plasma concentrations of CML and CEL were 2.80 (0.40) μmol/L (range, 2.1–3.4 μmol/L) and 0.82 (0.21) μmol/L (range, 0.5–1.2 μmol/L), respectively. In hemodialysis (n = 17) and peritoneal dialysis (n = 9) patients, plasma concentrations of CML and CEL were increased two- to threefold compared with controls, without significant differences between dialysis modes [7.26 (1.36) vs 8.01 (3.80) μmol/L (P = 0.89) for CML, and 1.84 (0.39) vs 1.71 (0.42) μmol/L (P = 0.53) for CEL].

Conclusions: This stable-isotope-dilution tandem mass spectrometry method is suitable for simultaneous analysis of CML and CEL in hydrolysates of plasma proteins. Its robustness makes it suitable for assessing the value of these compounds as biomarkers of oxidative stress resulting from sugar and lipid oxidation.

Prevalence of anemia in patients admitted to hospital with a primary diagnosis of congestive heart failure

OBJECTIVES

To find the prevalence of anemia in patients hospitalized with the primary diagnosis of congestive heart failure (CHF).

BACKGROUND

There is growing evidence that anemia is common in CHF and may contribute to the high morbidity and mortality associated with this condition. However, there is considerable disagreement about the prevalence of anemia in this condition.

METHODS

In 338 consecutive patients who were admitted to the medical wards with a primary diagnosis of CHF we extracted from the charts the hemoglobin (Hb), serum creatinine, age, sex, New York Heart Association (NYHA) functional class, presence of smoking, diabetes, hypertension, hyperlipidemia and the primary cardiac etiology of the CHF. Anemia was considered to be present when the Hb on admission was <12 g/dl.

RESULTS

All the patients were NYHA functional class III-IV. One hundred seventy seven (52.4%) of the 338 patients had a Hb on admission that was <12 g/dl. The mean Hb for the entire group was 12.0+/-1.8 g/dl. One hundred three (51.0%) of the 202 males were anemic compared to 74 (54.4%) of the 136 women. The mean serum creatinine was 1.7+/-1.1 mg/dl. The prevalence of renal insufficiency (serum creatinine >1.5 mg%) was 47.6%. There was a negative correlation between the level of serum creatinine and Hb (r=-0.294) P<0.00001. Of the 177 patients who were anemic, most of 114 (64.4%) had a serum creatinine >1.5 mg/dl.

CONCLUSIONS

Anemia is a common finding in patients hospitalized with CHF and most anemic CHF patients have some degree of renal insufficiency. In view of the negative effect of anemia on cardiac function, it may be a common and important contributor to the mortality and morbidity of CHF in these patients.

Association between serum homocysteine and markers of impaired kidney function in adults in the United States

BACKGROUND

Circulating homocysteine, a risk factor for cardiovascular disease (CVD), is often elevated in chronic kidney disease and end-stage renal disease (ESRD) patients. Little is known about the risk of elevated homocysteine associated with less advanced renal insufficiency in the community.

METHODS

Serum homocysteine concentration measures (umol/L) from the National Health and Nutrition Examination Survey (NHANES) 1991-1994 participants who were aged >/=40 years and fasted >/=6 hours (1558 men and 1829 women) were categorized as <9, 9 to 11.9, 12 to 14.9, and >/=15. Renal function levels were determined by Modified Diet in Renal Disease (MDRD) estimated glomerular filtration rate (GFRest) (mL/min/1.73 m(2)) and the urinary albumin-to-creatinine ratio (ACR) (mg/g). Cumulative odds ratios (OR) of exceeding any given homocysteine cut point were computed by gender, using ordinal logistic regression. Each model included GFRest (<60, 60 to 90, >/=90), ACR (<15, 15 to <30, >/=30), age, race/ethnicity, red blood cell folate, serum vitamin B(12), and dietary vitamin B(6) intake as independent variables.

RESULTS

The adjusted ORs for elevated homocysteine risk were 9 to 11 times greater in adults with the lowest GFRest levels (<60 mL/min/1.73 m(2)) compared to those with normal GFRest levels. Association measures for marginal GFRest levels (60 to 90 mL/min/1.73 m(2)) were weaker but significant. Albuminuria (ACR >/=30 mg/g) was a significant, independent renal risk factor for elevated homocysteine in men and women (adjusted OR = 1.78, 95% CI 1.08-2.93, and adjusted OR = 1.83, 95% CI 1.21-2.76, respectively) relative to those with low normal albumin excretion, but high normal albuminuria (ACR = 15-30 mg/g) was not.

CONCLUSION

In the general population, renal insufficiency is strongly associated with an increased risk of elevated circulating homocysteine, independent of B vitamin status. These results raise the possibility that elevated homocysteine may be an important risk factor to explain the heavy burden of CVD associated with kidney disease.

Effect of ammonium chloride and dietary phosphorus in the azotaemic rat. I. Renal function and biochemical changes

BACKGROUND

Both dietary phosphorus restriction and the ingestion of ammonium chloride (NH(4)Cl) given to rats on a high-phosphorus diet have been shown to preserve renal function in the azotaemic rat. Parathyroidectomy also has been reported to preserve renal function and, in addition, to prevent kidney hypertrophy in the remnant kidney model. Our goals were (i) to evaluate in azotaemic rats the effect of dietary phosphorus on renal function in a shorter time frame than previously studied and (ii) to determine whether NH(4)Cl administration (a) enhances the renoprotective effect of dietary phosphorus restriction and (b) improves renal function in the absence of parathyroid hormone (PTH).

METHODS

High (H; 1.2%), normal (N; 0.6%) and low (L; <0.05%) phosphorus diets (PD) were given for 30 days to 5/6 nephrectomized rats. In each dietary group, one-half of the rats were given NH(4)Cl in the drinking water. The six groups were HPD + NH(4)Cl, HPD, NPD + NH(4)Cl, NPD, LPD + NH(4)Cl and LPD. The effect of NH(4)Cl administration was also evaluated in 5/6 nephrectomized, parathyroidectomized (PTX) rats on NPD.

RESULTS

In each of the three dietary phosphorus groups, creatinine and urea clearances were greater (P<0.01) in rats receiving NH(4)Cl. Neither creatinine nor urea clearance was reduced by high dietary phosphorus. Urine calcium excretion was greatest in the LPD group and was increased (P < or = 0.001) in all three groups by NH(4)Cl ingestion. An inverse correlation was present between plasma calcium and phosphorus in the parathyroid intact (r = -0.79, P<0.001) and PTX groups (r = -0.46, P = 0.02). In PTX rats, NH(4)Cl ingestion increased (P < or = 0.01) creatinine and urea clearances and both an increasing plasma calcium concentration (r = 0.67, P<0.001) and urine calcium excretion (r = 0.73, P<0.001) increased urine phosphorus excretion.

CONCLUSIONS

At 30 days of renal failure (i) NH(4)Cl ingestion increased creatinine and urea clearances, irrespective of dietary phosphorus; (ii) high urine calcium excretion, induced by dietary phosphorus restriction and NH(4)Cl ingestion, did not adversely affect renal function; (iii) high dietary phosphorus did not decrease renal function; (iv) the absence of PTH did not preserve renal function or prevent NH(4)Cl from improving renal function; and (v) both an increasing plasma calcium concentration and urine calcium excretion resulted in an increase in urine phosphorus excretion in PTX rats.

Renal insufficiency in long-term lithium treatment

OBJECTIVE

To compare long-term lithium patients who developed renal insufficiency (RI) with those who did not, and to examine what characterized these groups.

METHOD

One hundred fourteen subjects with DSM-IV bipolar, major depressive, or schizoaffective disorder who had been taking lithium for 4 to 30 years from 1968 to 2000 were studied retrospectively. Subjects with blood creatinine levels > or = 1.5 mg/dL were defined as RI patients, and creatinine levels < 1.5 mg/dL indicated no renal insufficiency (NRI). Ninety-four unmedicated subjects, matched for sex and age, served as a comparison group and had 2 measures of creatinine with a mean interval of 11.88 years.

RESULTS

Twenty-four (21%) of the lithium-treated patients were defined as RI patients. These subjects exhibited the "creeping creatinine" phenomenon as their creatinine levels increased progressively. The NRI subjects showed no increase of creatinine levels in up to 30 years and remained comparable to the comparison group. RI was associated with episodes of lithium intoxication and diseases or medicines that could affect glomerular function, but not with sex, psychiatric diagnosis, age at onset of diagnosed disorder, duration of lithium therapy, serum lithium concentration, and cumulative lithium dose.

CONCLUSIONS

Long-term lithium therapy did not influence glomerular function in an overwhelming majority of patients. However, about 20% of long-term lithium patients exhibited "creeping creatinine" and developed renal insufficiency.

A feeling in the waters: diagnosis of heart failure using urinary natriuretic peptides

Plasma levels of brain natriuretic peptide (BNP) and N-terminal pro-BNP (N-BNP) are highly sensitive markers of ventricular dysfunction and/or hypertrophy and, in established disease, offer prognostic value and may be useful for guidance of therapy. Ng and co-workers report in this issue of Clinical Science that urinary levels of N-BNP may be as useful as plasma levels for the discrimination of patients with and without heart failure. This raises the potential for a relatively simple urine test that could be used for the diagnosis of heart failure. Roles in prognostication and the guidance of therapy may also be possible but, perhaps of most significance, measurement of urinary N-BNP may be applied to screening of patients at high risk of heart failure. The main limitations of the study were that the sample of heart failure patients comprised only 34 individuals with New York Heart Association functional Class IV and that the observed correlation between levels of urinary N-BNP and plasma creatinine seemed counter-intuitive. The latter issue needs clarification, as renal impairment is a frequent co-morbidity among patients with heart failure and will potentially confound any observed association between ventricular dysfunction and urinary N-BNP levels. Another caveat is that it is unclear if testing for urinary N-BNP can be cheaply and conveniently administered on a large scale. Nevertheless, this first demonstration of elevated N-BNP in the urine of patients with heart failure raises a number of exciting possibilities with regard to the management of patients with established or possible heart failure. Further investigation is required and eagerly awaited.

Granulocyte extravasation and recruitment to sites of interstitial inflammation in patients with renal failure

BACKGROUND

We have shown that leukocytes collected from sites of interstitial inflammation in patients on hemodialysis have a disturbed expression of CD11b compared to cells from healthy subjects. The aim of the present study was to study adhesion molecule expression on granulocytes in the peripheral circulation and at sites of interstitial inflammation in patients with renal failure.

METHODS

Two skin blisters were raised in 10 patients and 19 healthy subjects and interstitial exudates collected (0 h). Skin chambers were applied and exposed to buffer or serum for 10 h in order to induce an intermediate and an intense interstitial inflammation. Cells and blister fluid were collected for determination of leukocyte count, CD11b/CD62L expression, interleukin-8 (IL-8) concentration in the interstitium and blister activity in terms of CD11b up-regulation.

RESULTS

At the sites of intermediate and intense inflammation, granulocytes from patients with renal failure showed significantly higher expression of CD62L (p < 0.01 and p < 0.001, respectively) and significantly lower expression of CD11b (p < 0.0001 and p < 0.0001, respectively) compared to corresponding cells from healthy subjects. The interstitial concentration of IL-8 was significantly lower at the sites of intermediate (p < 0.005) and intense inflammation (p < 0.05) in patients with renal failure compared to in healthy subjects. In order to explore whether the decreased CD11b expression observed in patients is due to the interstitial milieu, blister exudates from patients and healthy subjects were incubated with leukocytes from healthy blood donors. Blister exudates from patients had a similar capacity to mobilize CD11b on granulocytes in vitro compared with blister exudates from healthy subjects. There was no consistent correlation between the expression of adhesion molecules on granulocytes in the interstitium and the concentration of IL-8 or the total interstitial concentration of chemotactic mediators.

CONCLUSION

Constitutive cellular determinants are probably involved in the disturbed expression of adhesion molecules on granulocytes at sites of interstitial inflammation in patients with renal failure.

Assessing thyroid hormone status in a patient with thyroid disease and renal failure: from theory to practice

A 35-year-old Asian male, treated for hyperthyroidism, systemic lupus erythematosis, and uremia presented with low serum total thyroxine (T4) and normal serum thyrotropin (TSH) levels. He had been receiving prednisone and methimazole for 15 weeks. Free T4 measured by direct equilibrium dialysis was in the hypothyroid range (0.3 ng/dL; normal, 0.8-2.7). Two possibilities were considered: (1) a weakly bound dialyzable inhibitor in uremic serum that interfered with this serum free T4 determination or (2) hypothyroidism with persistent TSH suppression because of prior hyperthyroidism. To determine whether a weakly bound inhibitor was involved, the patient's serum was serially diluted using two diluents: (1) an ultrafiltrate of the patient's serum, which would contain any unbound inhibitor, as well as free T4 and (2) an inert diluent. Free T4 measurements were similar with both, providing evidence against the presence of a dialyzable and ultrafilterable inhibitor. In conclusion, this patient was hypothyroid because of antithyroid drug administration, associated with prolonged central TSH suppression from preexisting hyperthyroidism. Discontinuation of methimazole resulted in normalization of serum total T4 and TSH values. Thus, paired, serial serum dilutions, using two different diluents, provided evidence for differentiation of appropriately low free T4 measurements (because of hypothyroidism), from spuriously low free T4 measurements (because of an interfering inhibitor).

Progression of renal insufficiency in type 2 diabetes with and without microalbuminuria: results of the Heart Outcomes and Prevention Evaluation (HOPE) randomized study

BACKGROUND

In patients with type 2 diabetes with overt nephropathy, the risk for progressive renal failure is high. This risk is less well established for those with type 2 diabetes and microalbuminuria or normalbuminuria. We studied changes in serum creatinine levels during 3.5 to 5.5 years in a large cohort of people with diabetes at high cardiovascular risk with microalbuminuria or normalbuminuria.

METHODS

Retrospective analysis of serum creatinine levels at baseline and yearly thereafter was performed in the Microalbuminuria and Renal Outcomes in the Heart Outcomes and Prevention Evaluation study comparing ramipril's effects with placebo during 4.5 years in 3,577 participants with diabetes, including 1,139 participants with microalbuminuria and 333 participants with renal insufficiency. Participants with dipstick-positive proteinuria (>1+) or serum creatinine levels greater than 2.3 mg/dL (200 micromol/L) were excluded.

RESULTS

Serum creatinine levels did not increase significantly during the study if all participants with diabetes are considered or for subgroups with microalbuminuria and/or renal insufficiency at baseline. However, slopes of serum creatinine over time showed a significant trend for increasing values. There were no differences between the placebo and ramipril-treated groups. A serum creatinine level of 1.4 mg/dL (125 micromol/L) or greater newly developed in 474 of 3,238 people (243 patients, placebo; 231 patients, ramipril; P = 0.5033). A doubling of baseline serum creatinine level or end-stage renal disease developed in 8 of 333 participants with renal insufficiency at baseline.

CONCLUSION

In people with type 2 diabetes, but without overt nephropathy, who are at high risk for cardiovascular disease, progression of renal insufficiency is slow on the basis of changes in creatinine levels. On the basis of reaching threshold levels of renal function, progression rates are clinically meaningful, especially considering population life expectancy.