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Background: Serum cardiac troponin concentrations are commonly increased in end-stage renal disease (ESRD) in the absence of an acute coronary syndrome (ACS). The data on cardiac troponin I (cTnI) are more variable than those for cardiac troponin T (cTnT). There is little information on cardiac troponin concentrations in patients with chronic kidney disease (CKD) who have not commenced dialysis., Methods: We studied 222 patients: 56 had stage 3 (moderate CKD); 70 stage 4 (severe CKD); and 96 stage 5 (kidney failure). Patients underwent echocardiography and were followed prospectively for a median of 19 months; all-cause mortality was recorded., Results: Overall, serum cTnT was increased above the 99th percentile reference limit in 43% of all CKD patients studied, compared with 18% for cTnI. Serum cTnT and cTnI concentrations were more commonly increased in the presence of more severe CKD (11 and 6 patients in stage 3, 27 and 8 in stage 4, and 57 and 24 in stage 5 (P < 0.0001 and <0.02, respectively). Among 38 patients with detectable cTnI, 32 had detectable cTnT (r(s) = 0.67; P < 0.0001). There was evidence that decreasing estimated glomerular filtration rate increased the odds of having detectable cTnT (P < 0.001) but not cTnI (P = 0.128). There was no evidence to support an adjusted association of detectable cardiac troponins with increasing left ventricular mass index. Increased cTnT (P = 0.0097), but not cTnI, was associated with decreased survival., Conclusions: Increased cTnT and cTnI concentrations are relatively common in predialysis CKD patients, in the absence of an ACS, including among those with stage 3 disease. The presence of left ventricular hypertrophy alone does not explain these data. Detectable cTnT was a marker of decreased survival.

Background: Overexpression of glutathione S-transferase (GST; EC 2.5. 1.18) has been documented in the erythrocytes of patients with chronic renal failure, and this event may well be of relevance from a clinical standpoint. In fact, it could serve as a marker of uremic toxicity overall, which can contribute to impair the function and survival of the erythrocytes. However, the biochemical details of this phenomenon are poorly understood., Methods: In this study, we characterized the expression of GST in erythrocytes of 118 uremic patients under different clinical conditions. The mechanisms responsible for the regulation of protein expression and enzyme activity were investigated in light of different dialysis approaches, oxidative stress, uremic toxins, erythrocyte age, and erythropoietin (EPO) supplementation., Results: Mean GST activity in uremic patients was highly overexpressed with respect to controls, and this phenomenon was exclusively attributable to an increased expression of GST. Overexpression of GST did not appear to be dependent on oxidative stress and was not influenced by vitamin E supplementation. In the same manner, both erythrocyte age and EPO supplementation apparently did not interfere with the GST concentrations, which were the same in controls and patients. Preliminary experiments suggested that high-molecular weight or protein-bound toxins could play some role in the overexpression of GST., Conclusions: GST expression may be a useful marker for the individual accumulation of uremic toxins as well as of the efficiency of new dialysis strategies in removing them.

HPLC was used to study the effectiveness of two different desferrioxamine (DFO) administration strategies (15 mg/kg DFO, 1 h or 44 h before dialysis) on generation of aluminoxamine and ferrioxamine in five hemodialysis patients. The percentage of ultrafilterable aluminum and iron in these patients was also investigated by electrothermal atomic absorption spectrometry. The administration of DFO in both schemes increased the ultrafilterable serum aluminum concentrations from a mean of 17.1 +/- 1.6% to a mean of 75.7 +/- 14.1%. However, 1 h after DFO infusion, only 38.8 +/- 7.7% of the total serum aluminum was bound to DFO; 44 h after DFO infusion, only 15.8 +/- 8.0% was bound. Similar results were obtained for ferrioxamine. These results suggest that the ultrafilterable serum fraction contains aluminum and iron chelated by DFO and by DFO metabolites, which retain similar metal-chelating abilities.

We have previously shown that the Nichols assay for intact parathyroid hormone (I-PTH) reacts with a non-(1-84) molecular form of PTH. This form behaves as a carboxy-terminal fragment and accumulates in renal failure, accounting for 40-60% of the measured immunoreactivity. We wanted to see whether this was a common event with other commercial two-site I-PTH assays. We thus compared the ability of three commercial kits [Nichols (NL), Incstar (IT), and Diagnostic System Laboratories (DSL)] to measure I-PTH in 112 renal failure patients and to detect hPTH(1-84) and non-(1-84)PTH on HPLC profiles of serum pools from uremic patients with I-PTH concentrations of 10-100 pmol/L. The behavior of synthetic hPTH(7-84), a fragment possibly related to non-(1-84)PTH was also compared with hPTH(1-84) in the three assays. The I-PTH concentrations measured with the three assays in the 112 uremic samples were highly related (r2 > or = 0.89, P < 0.0001), and the values measured with NL were, on average, 23% higher than IT. Values measured with DSL were 23% and 56% higher than IT for values less than and more than 40 pmol/L, respectively. The three assays detected two HPLC peaks on four different profiles corresponding to hPTH(1-84) and non-(1-84)PTH. This last peak represented 36 +/- 8.4% of the immunoreactivity with NL, 24 +/- 5.5% with IT, and 25 +/- 2.8% with DSL (NL vs IT or DSL: P < 0.05). These differences were confirmed by a 50% lower immunoreactivity to hPTH(7-84) compared with hPTH(1-84) for IT and DSL but not for NL. These results suggest that most of the two-site I-PTH assays would cross-react with non-(1-84)PTH material, thus explaining about one-half of the 2-2.5 x higher I-PTH concentrations reported in uremic patients without bone involvement than in subjects without uremia.

To elucidate the mechanism of impaired serum binding of furosemide observed in patients with renal dysfunction, we examined in vitro the serum protein binding of furosemide in the absence and presence of uremic toxins that are endogenously retained solutes in uremic serum and act as inhibitors of drug binding. Analysis of the binding data of furosemide at its therapeutic concentration (6.6 mg/L) indicated that, among the four uremic toxins studied, 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) showed the greatest inhibitory potency for the binding of furosemide to serum; moreover, the inhibition was competitive. CMPF thus most likely represents the primary determinant for the serum binding defect of furosemide in uremia. However, CMPF and oleate appear to exert a synergistic effect on the inhibition of furosemide serum binding--perhaps through a cascade effect on furosemide-binding inhibition in the oleate-CMPF-furosemide system, in which the binding of oleate to its low-affinity sites indirectly displaces furosemide from albumin and thus increases the transiently liberated CMPF molecules. Similar cascade effects on furosemide binding in the presence of CMPF were also originated by other long-chain (C18) fatty acids, linoleate and stearate, although to a lesser extent. Because CMPF is not effectively removed by ordinary hemodialysis treatment, the combined direct and cascade effects of CMPF and fatty acids appear to contribute to the increase in the free fraction of furosemide during hemodialysis.

The major phenytoin metabolite, 5-(p-hydroxyphenyl)-5-phenylhydantoin glucuronide (HPPG), was primarily responsible for the positive bias noted when uremic specimens were assayed with the Abbott TDx Free Phenytoin fluorescence polarization immunoassay. The amount of bias depended on both HPPG and phenytoin concentration, increasing with increases in either concentration. The new Abbott TDx II assays for phenytoin and free phenytoin exhibited no significant cross-reactivity with HPPG and no bias in clinical specimens from uremic patients. Both assays correlated well with Emit-based assays (r >0.98), had CVs of <3.5%, and had minimum detection limits of <0.1 mg/L. Calibration curves were stable for at least 6 weeks. All of the TDx assays cross-reacted with another metabolite, 5-(p-hydroxyphenyl)-5-phenylhydantoin (HPPH), but expected HPPH concentrations are too low to cause a clinically significant bias. The Emit-based phenytoin assay exhibited a significant matrix effect when calibrators were prepared in defibrinated plasma processed to resemble serum.

Concentrations of pentosidine, an advanced glycation end product, are increased in aging, diabetes mellitus, and uremia. Using HPLC with column switching, we developed a direct method of measuring pentosidine in urine and serum. We inject the sample directly onto a gel-filtration precolumn, select ("heart-cut") the eluate fraction containing pentosidine, and introduce this fraction into a reversed-phased column by use of a switching valve. The recovery rate of the complete method was 97.7-99.9%. The intraassay CV was 5.7%, and the interassay CV was 5.8%. The calibration curve showed significant linearity (r = 0.998, P = 0.0001). We examined urinary concentrations of pentosidine in 12 diabetic patients (mean +/- SD, 8.7 +/- 2.3 micromol/mol of creatinine), 32 patients with chronic renal failure (CRF; 36.1 +/- 39.0), 19 osteoporotic patients (7.9 +/- 5.3), and 29 healthy control subjects (5.2 +/- 2.3). In CRF, urinary pentosidine in the patients undergoing hemodialysis was significantly higher than in CRF patients not being treated by hemodialysis (mean, 58.1 vs 18.2; P <0.001). Also, concentrations of urinary and serum pentosidine were significantly correlated (r = 0.797, P = 0.0011). Because this method does not require pretreatment of samples, it is convenient and useful for measuring urinary and serum pentosidine.

We developed a new method for measuring serum 1,5-anhydroglucitol (1,5-AG), using liquid chromatography/atmospheric pressure chemical-ionization mass spectrometry (LC/MS). With this method we measured serum 1,5-AG concentrations in uremic and diabetic patients and compared these values with those determined by an enzymatic method. Serum 1,5-AG concentrations were significantly less in the undialyzed and dialyzed uremic patients and in diabetic patients; the values in the dialyzed patients decreased after hemodialysis. In uremic patients with high concentrations of serum myo-inositol, the 1,5-AG values determined by LC/MS were significantly lower than those determined enzymatically. There was no significant correlation between 1,5-AG and fructosamine in the uremic patients. These results demonstrate that serum 1,5-AG cannot be used as an index for glycemic control in uremic patients and that the LC/MS method is indicated in uremic patients with high concentrations of myo-inositol.

Pentosidine is a fluorescent cross-link compound that accumulates in human tissues from uremic and diabetic patients. Using SP-Sephadex C-25 pretreatment before reversed-phase HPLC, we developed a method for quantifying pentosidine in the acid hydrolysate of serum. We examined concentrations of pentosidine in serum from 98 patients with end-stage renal disease requiring hemodialysis and from 33 normal control subjects. The mean (+/- SD) concentration of pentosidine was significantly greater in serum from uremic patients than that from control subjects (1267 +/- 695 nmol/L vs 77 +/- 40 nmol/L, P = 0.0001). There was a significant correlation between serum pentosidine concentrations and age in control subjects (r = 0.453, P < 0.01), but not in uremic patients. Serum pentosidine significantly increased with the duration of hemodialysis treatment (r = 0.272, P < 0.05). The greater pentosidine concentrations in uremic patients may be caused by the increased synthesis of pentosidine (perhaps because of the retention of pentosidine precursors), by the retention of pentosidine molecule itself in end-stage renal failure, or both.

Accumulation of phenytoin metabolites in uremia has been shown to interfere with some immunoassay methods for phenytoin measurement. We evaluated the effects of uremia (serum creatinine > 13 mg/L) on free and total phenytoin concentrations measured by the Abbott TDx fluorescence polarization immunoassay, and the DuPont aca and Syva EMIT homogeneous enzyme-multiplied immunoassay methods, using HPLC as the comparison method. In uremic patients, the TDx assay showed both fixed and proportional bias in comparison with the HPLC for both total phenytoin concentration (TDx = 1.24 x HPLC + 1.9 mg/L) and free phenytoin concentration (TDx = 1.52 x HPLC + 0.24 mg/L). The total bias was as great as 100% for both total and free phenytoin. Cross-reactive substances other than 5-(p-hydroxyphenyl)-5-phenylhydantoin (HPPH) and HPPH-glucuronide appeared to be responsible. In contrast, there was minimal interference with aca and EMIT assays.

We developed a simple and sensitive high-performance liquid chromatographic (HPLC) method that uses fluorescence as a detector for quantifying serum phenol and p-cresol in uremic patients on hemodialysis. Identification of phenol and p-cresol was confirmed by liquid chromatography/mass spectrometry. Because the HPLC method requires only simple extraction by ethyl acetate and does not require further steps such as derivatization, it is simple and rapid compared with gas chromatography or gas chromatography/mass spectrometry. Concentrations of phenol and p-cresol in uremic serum were significantly (p < 0.01) higher than those in normal serum. Reduction rates of phenol and p-cresol by hemodialysis were lower than those of urea and creatinine, suggesting a protein-binding property of phenol and p-cresol. This method will be useful for monitoring serum phenols in dialyzed patients as an index of hemodialysis adequacy.

An equilibrium model for the speciation of Al3+ in normal serum has been developed in which 81% of the aluminum is bound to transferrin. The remaining 19% exists primarily as Al(PO4)(OH)-, with minor amounts of citrate and hydroxide species. The model meets several key criteria. The concentration of free aluminum is below the upper limit set by the solubility product of aluminum phosphate. The fraction of low-molecular-mass aluminum species agrees with experimental studies on the fraction of ultrafiltrable aluminum in both normal and uremic serum. Lastly, the model accounts for the relative effectiveness of EDTA, citrate, and desferrioxamine B for binding aluminum in serum by including competition from zinc, magnesium, and calcium for these ligands. Uncertainties in the available thermodynamic database are discussed.

To validate azotemic markers as an index for intradialytic changes in solute concentration, we compared eight solutes (pseudouridine, xanthine, hypoxanthine, peak 4, peak 5, p-hydroxyhippuric acid, indoxyl sulfate, and hippuric acid) with five classical azotemic markers (urea, creatinine, uric acid, phosphate, and potassium). We determined concentrations by reversed-phase HPLC coupled to ultraviolet absorption or photometrically. Seven compounds showed significant intercorrelation (P less than 10(-5)): urea, pseudouridine, uric acid, peaks 4 and 5, p-hydroxyhippuric acid, and creatinine. The hippuric acid concentration change after dialysis correlated with the change for these seven compounds and also with indoxyl sulfate, hypoxanthine, potassium, and the group of unidentified ultraviolet-absorbing HPLC peaks accumulating in uremia. We conclude that urea only partially represents the concentration changes of other retention compounds after dialysis; alternative markers, e.g., hippurate, should be considered.

We have developed an HPLC method for measuring carbamylated hemoglobin (CarHb), based on the quantification of valine hydantoin formed from the released NH2-terminal carbamyl valine residue after acid hydrolysis of hemoglobin. In uremia, CarHb is produced by nonenzymatic post-translational modification of the terminal amino group of hemoglobin monomers by isocyanic acid, derived from the spontaneous dissociation of urea. We measured CarHb in 25 nonuremic control subjects, 24 nonuremic diabetic subjects, and 30 patients with stable chronic renal failure. There was no significant difference between the controls and diabetic patients, their mean (SD) CarHb values being 41 (11.5) and 38 (10.8) micrograms of carbamyl valine per gram of hemoglobin (microgram CV/gHb), respectively. Mean (SD) CarHb values in the uremic patients were much greater, 164 (87.7) microgram CV/gHb. There was significant correlation between the concentrations of CarHb and plasma urea in the uremic subjects. Thus CarHb provides a urea-derived index of chronic uremia.

Organic anions accumulated in blood serum of patients with chronic renal failure were separated by a novel technique: closed-system capillary zone electrophoresis (CZE) in a pH6 carrier-electrolyte system. Hippuric acid (HA), p-hydroxyhippuric acid, and uric acid were identified by their co-elution with standards prepared in ultrafiltered normal serum and by comparison with the corresponding ultraviolet-detected peaks positively identified in the HPLC analyses. Analysis time for the entire profile is 8 min. Repeatabilities (CVs) of CZE migration times and peak areas of the three acids in serum samples were about 0.7% and 6%, respectively. We quantified HA in 10 ultrafiltered uremic serum samples and compared results with those by a previously described HPLC procedure. The very good agreement further supports the identification of hippuric acid. Accuracy and precision of the CZE method were similar to those for the HPLC gradient-elution method, but analysis time for HA (8 min) is much less than by HPLC (90 min). Our technique is very suitable for selective, rapid analysis for (ultraviolet-absorbing) anionic constituents in ultrafiltered uremic serum, without any sample pretreatment.

We measured phospholipase A2 (PLA2; EC 3.1.1.4) activity in normal and uremic plasma, using [1-14C]oleate-labeled autoclaved Escherichia coli as substrate. Hydrolysis of bacterial phospholipid by crude plasma from both groups was optimal at pH 5.5, was specific for the 2-acyl position of phospholipids, and had an absolute requirement for calcium. Activity was greatest in the presence of added Ca2+, 5 mmol/L, but this increase was inhibited by several divalent cations (Mg2+, Zn2+, Cu2+, Ba2+, Co2+, Pb2+, Fe2+) and by Fe3+. PLA2 activity was also inhibited by heparin at acid and alkaline pH, normal plasma being more sensitive than uremic plasma to this inhibition. Enzyme activity in undiluted plasma was eightfold greater in uremic than in normal plasma. Dilution of plasma by two to fourfold increased the total activity of both normal and uremic plasma. However, the relative differences in total activity between the groups remained constant (eight- to 11-fold). The cause and consequences of the increased PLA2 activity in uremia remain to be established.

Uremic ultrafiltrates (and normal serum, for comparison) were fractionated by means of gel filtration. The collected fractions were further investigated by combined analytical techniques: "high-performance" liquid chromatography, gas chromatography, mass spectrometry, and isotachophoresis. Ultrafiltrate fractions in the so-called middle molecular mass region (Mr 500-2000) contained a considerable amount of substances of low molecular mass, such as carbohydrates, organic acids, amino acids, and ultraviolet absorbing solutes. Ultraviolet absorbance in the "middle molecular mass region" of the gel chromatogram is mainly due to the presence of these rather low-molecular-mass solutes. Therefore this signal is not a quantitative measure of molecules with a "middle" molecular mass.

A semi-automated two-stage chromatographic system is described for use in evaluating neurotoxin b4-2 in body fluids of uremic patients and healthy subjects. The only manual step is the injection, thus decreasing the risk of operator error inherent in the previous manual method (Clin Chem 29: 703-707, 1983) and concurrently improving CV from 9% to 6.4% as measured during a 16-month period.

Using our newly developed ion-pairing reversed-phase liquid-chromatographic method for assay of indoxyl sulfate, we measured its concentration in plasma of normal subjects and patients in various degrees of renal failure. Response was linear over the range of 50 to 25 000 pmol of indoxyl sulfate injected into the chromatograph. We demonstrated the specificity of the assay for azotemic plasma by using enzymatic conversion with a sulfatase. For a moderately above-normal indoxyl sulfate concentration in azotemic plasma of 134 mumol/L (29 mg/L), the within-day CV was 1.6%, the day-to-day CV 2.8%. Mean analytical recovery was 101.0% (CV = 2.8%). Over a range of 29 to 192 mg of creatinine per liter of plasma (x), indoxyl sulfate (y) concentration (in mumol/L) was positively correlated (y = 1.30x + 0.43). This method should prove valuable for further study of uremic toxins.

We estimated glycated ("glycosylated") hemoglobin in erythrocytes of hemodialyzed uremic patients by the aminophenylboronic acid affinity-chromatographic method and by an ion-exchange chromatographic method. As expected, apparent HbA1 concentrations were above normal in the uremic patients, owing to interference by the carbamylated hemoglobin. However, there was no significant difference between values for uremic and normal subjects when glycated hemoglobin was measured by the affinity method. Evidently it is unaffected by the presence of hemoglobin species modified by reactants not displaying a cis-1,2-diol group, such as carbamylated hemoglobin. For this reason it is preferable to the ion-exchange chromatographic method for accurate measurement of glycated hemoglobin.

We describe a method for comparing plasma samples from healthy subjects and from chronic uremic patients before and after dialysis. It was used to determine the nature of those metabolites that appear to characterize the uremic state. Preliminary fractionation of the metabolites by gel chromatography was followed by removal of the aqueous effluent by lyophilization and preparation of volatile trimethylsilyl derivatives, which were then examined by gas-liquid chromatography. Gas-liquid chromatography/mass spectrometry was used to characterize and identify individual metabolites. Gas-liquid chromatographic patterns of plasma from healthy and uremic subjects differ markedly, more so than do individual plasma samples within the same class of subjects. Concentrations of many metabolites are increased in uremia, but after dialysis of the patient's blood, the concentrations become about the same as those in healthy plasma. We have observed some 150-200 metabolites in each category of plasma. We have tentatively identified about a tenth of the compounds that appear to be specific to or increased in uremia, including lactic acid, glycerol, erythritol, erythronic acid, 2-deoxy erythro pentonic acid, arabinitolarabinonic acid, inositol, and lactose. Some of these are present in concentrations greater than 20 mg/liter and have not been previously reported as occurring in the uremic state.

We measured the fluorescence, at various excitation (Ex) and emission (Em) wavelengths, of serum ultrafiltrates and fractions of serum resolved by chromatography on Sephadex G15, studying both normal subjects and patients in chronic renal failure requiring hemodialysis. We found hitherto undescribed fluorescence at Ex 380 nm/Em 440 nm and Ex 400 nm/Em 460 nm, the intensity being greatly increased in patients with chronic renal failure in comparison with normal subjects (p less than 0.005). This fluorescence persisted unaltered when serum was filtered through membranes having cutoffs ranging from 10 000 to 500 Da. Each serum fraction resolved by gel chromatography demonstrated a characteristic fluorescence, which was generally much more intense in uremics. The most intense fluorescence (Ex 380 nm/Em 440 nm and Ex 400 nm/Em 460 nm) was emitted in the higher-Mr fractions.

Results obtained with a potentiometric analyzer, NOVA 1, specific for sodium and potassium, were compared with those by flame photometry. Both instruments showed linearity within a physiological range of sodium and potassium concentrations and had similar precisions. Volume displacements from addition of albumin or Intralipid to aqueous samples yielded the predicted lower flame-photometric results because of the relative decrease in sample water. There may be a small interaction between sodium and albumin. Physiological measurements on plasma from uremic patients showed no change after dialysis that could be ascribed to a decrease in interaction of these ions with creatinine and urea. Potentiometric values for sodium and potassium did not differ significantly, whether measured in cerebrospinal fluid or in the corresponding plasma. Results for urine were the same potentiometrically and by flame photometry.

A compound present in normal urine and in ultrafiltrates of uremic plasma in the fraction of so-called "uremic middle molecules" was isolated by liquid chromatography. Preliminary studies, including amino acid analysis, characterization of uronic acids, and ultraviolet spectroscopy, show that the molecule contains glycine, a uronic acid, and an aromatic ring. Characterization by 1H and 13C nuclear magnetic resonance spectrometry shows conclusively that this compound is a double conjugate of glucuronidate--o-hydroxyhippuric acid, which has been previously described by Zimmerman et al., using quite different techniques of isolation and identification (Clin Nephrol 14: 107, 1980; FEBS Lett 129: 237, 1981).

Endogenous fluorescent substances increase in serum during uremia. We have used "high-performance" liquid chromatography to profile these fluorescent substances in both uremic and normal body fluids. The fluorescence excitation and emission maxima we used were 322 and 415 nm, respectively. Of the numerous fluorescent substances found in uremic body fluids and in normal urine, some were also detectable in normal serum, but at relatively weak fluorescence intensities.

We show that an indophenol-based colorimetric method for acetaminophen (Clin Toxicol 15: 67-73, 1979) has less than maximal sensitivity because of (a) incomplete hydrolysis, related to suboptimal acid concentration; (b) suboptimal hydrolysis time; and (c) possible deterioration of the ammonium hydroxide reagent after 2.5 months. We have modified the method by optimizing duration of hydrolysis and color development. Results by the method correlate linearly with acetaminophen concentrations to 250 mg/L (1.66 mmol/L). Moreover, the modified method is free from interference by compounds in serum from uremic patients.

An endogenous compound (included in the fraction of uremic toxins often called the "uremic middle molecules") was separated from plasma of uremic patients and urine from normal persons. As elucidated by mass spectrometry, enzymatic hydrolysis, and 1H, 13C nuclear magnetic resonance, it appears to be a conjugate of o-hydroxybenzoic acid with glucuronic acid. Its presence in urine of healthy subjects indicates its physiological character.

We determined, immunoturbidimetrically, the concentrations of apolipoprotein A-I (apo A-I) (a) in total serum, (b) in total lipoproteins, and (c) in the fraction of d greater than 1.21 kg/L (free apo A-I) in 31 uremic patients (16 on hemodialysis, HD, and 15 with end-stage renal failure, ESRF) and 14 control subjects. The concentration of free apo A-I in serum was significantly increased in both groups of uremic patients (0.27 +/- 0.07 g/L for HD and 0.22 +/- 0.08 g/L for ESRF, mean +/- SD), in comparison with the control group (0.14 +/- 0.04 g/L). The ratio of total apo A-I to high-density-lipoprotein cholesterol was significantly increased in sera from both uremic groups, whereas the apo A-I/HDL-chol ratio of total lipoproteins was similar in all three groups. No apo A-I could be detected in five ultrafiltrates of plasma, even after 100-fold concentration. Analysis of apo A-I isoforms by isoelectrofocusing revealed a significant relative increase in apo A-I3 and a decrease in apo A-I5 isoform in ESRF patients, but not in HD patients. Finally, we found no relationship between serum TG and free apo A-I concentration.

A popular colorimetric analysis for serum acetaminophen, based on ring-nitration of the drug, is demonstrated to yield both "false positives" and erroneously high results for serum from uremic patients. The interference appears to be anionic at physiological pH, and correlates significantly with serum creatine concentration and with the magnitude of the "anion gap." A modification of the analysis involving extraction of the acetaminophen with ether eliminates the interference. As little as 10 mg of drug per liter can be accurately measured in serum by the proposed procedure. Analytical recovery was 97% at a concentration of 1 g/L. Coefficients of variation for the analysis at respective concentrations of 100 and 500 mg/L were: within-run, 2.7% and 2.0%; between-run, 3.1% and 4.2%. I encountered no serious interferences from other drugs. The proposed method, rapid and reliable, is recommended for routine use in the clinical laboratory.

The clinical utility of glycated hemoglobin measurements in renal failure is controversial, given numerous earlier studies showing no correlation between glycated hemoglobin and other indicators of blood glucose control in uremic subjects. This problem is attributable, in part, to analytical interferences from carbamylated hemoglobins. We report use of a specific affinity method to measure glycated hemoglobins in a group of uremic patients, diabetic and nondiabetic, undergoing treatment by continuous ambulatory peritoneal dialysis. Concentrations of glycated hemoglobins correlated significantly with values for fasting plasma glucose (r = 0.52, n = 17, p less than 0.05) in these patients and with mean glucose measurements in five diabetic patients who used home glucose monitoring (r = 0.91, p less than 0.05). Contrary to studies with ion-exchange chromatography, our measurements of glycated hemoglobin showed no positive correlation with concentrations of urea in serum. In a separate group of patients, we found that hemodialysis sessions produced no acute effect on glycated hemoglobin. Measurements of glycated hemoglobins by analytically specific methods may thus better reflect long-term control of blood glucose in renal dialysis.

A major protein-bound ligand in the serum of chronic hemodialysis patients was isolated from heat-deproteinized uremic serum by "high-performance" liquid chromatography (HPLC). The isolated compound was identified as 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid by use of liquid secondary-ion mass spectrometry and gas chromatography-mass spectrometry. On HPLC, an authentic sample of this compound showed a retention time identical to that of the protein-bound ligand peak. The concentration of the furancarboxylic acid in serum, as estimated by HPLC, is markedly greater in chronic hemodialysis patients than in normal subjects.

Using reversed-phase "high-performance" liquid chromatography with fluorescence detection, we separated and identified some naturally fluorescent compounds in uremic serum and hemodialysate from patients with chronic renal disease. Several of the naturally fluorescent compounds were identified as indole derivatives by co-chromatography with authentic standards. In one specific case, the identity was confirmed by an enzymic peak-shift method. Compounds identified included indican, kynurenic acid, tryptophan, and 5-hydroxy-indole-3-acetic acid. Comparison of normal and uremic serum showed that the fluorescent materials are present in significantly greater concentrations in samples from uremic patients.

Chronic, low-grade, unexplained increases of total serum bilirubin concentration were observed in 16 of 132 (12%) chronic dialysis patients. Cessation of antihypertensive medication in four patients resulted in disappearance of hyperbilirubinemia. Propranolol was the only antihypertensive drug common to all 16 patients. Daily dosage varied among the patients, but the mean dose was 308 mg (+/- 51 SEM). Serial determinations of sera from individual patients given different doses and from the group as a whole demonstrated a linear relationship between propranolol dose and apparent total serum bilirubin concentration with continuous-flow analysis. When serum specimens from uremic patients receiving propranolol were treated with diazotized fulfanilic acid and examined spectrophotometrically, an absorbance peak distinct from but overlapping that of bilirubin was consistently demonstrated. The material producing the peak disappeared when the drug was stopped, did not dialyze, and was not reproduced by the in vitro addition of propranolol to uremic serum. We postulate that a metabolite(s) of propranolol is retained in uremic serum and interferes with the bilirubin determination.

An in vitro inhibitor of Na+/K+-transporting ATPase (EC 3.6.1.37) was isolated from uremic plasma and normal urine by liquid chromatography. A 23Na nuclear magnetic resonance study involving living erythrocytes showed that this inhibitor causes impairment of the Na+-K+ pump of intact erythrocytes. This finding may explain the high intra-erythrocytic sodium concentration in those uremic patients exhibiting a high concentration of this inhibitor. The presence of this same inhibitor in normal urine suggests that it may play a physiological role.

The use of 23Na nuclear magnetic resonance with aqueous shift reagent has made it possible to determine intracellular sodium concentrations in living erythrocytes. We applied this technique to samples from 16 healthy subjects and 41 uremic patients. The results seem to show distinct populations among the latter. Classically, two different relaxation times are obtained for intracellular sodium in biological media, according to relaxation NMR theory. Some patients, however, exhibit abnormal results that cannot be accounted for by this theory.

We evaluated the effect of azotemia on results for glycated hemoglobin as measured by a boronate-agarose affinity method and an ion-exchange chromatographic procedure with saline preincubation and found a good correlation. However, values for glycated hemoglobin in samples from nondiabetic patients with various degrees of azotemia were consistently higher with the ion-exchange column procedure (mean, 8.5%) than with the boronate affinity method (mean, 6.2%). The latter method may thus be preferred for monitoring glycated hemoglobin in diabetic patients with impaired renal function.