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An enzyme-spectrophotometric method to determine citrate in biological fluids is proposed, based on citrate lyase-catalyzed and phenylhydrazine reactions. The enzyme converts citrate into oxaloacetate, which, in the presence of phenylhydrazine, is transformed into the corresponding phenylhydrazone. The ultraviolet-absorbing product is determined by absorbance measurement at 330 nm. The method is more precise and twice as sensitive as the traditional citrate lyase method and, because it does not require the use of additional enzymes and coenzymes, is cheaper and simpler. Mean analytical recovery of citrate averaged 100.7% +/- 2.2%, imprecision (CV) of the assay for citrate at 0.96 mmol/L (urine) was 2.0%, and the lower limit of quantification was 0.08 mmol/L. Results correlated well with those by both ion-chromatographic and traditional citrate lyase methods.

A rapid and sensitive liquid chromatographic technique to determine L-glutamate: glyoxylate and aminotransferase (EC 2.6.1.4) activity in human liver is described. Homogenised tissue was incubated for 60 min in the presence of substrates and the 2-oxoglutarate generated was converted into the corresponding phenylhydrazone which was determined using reversed-phase high-performance liquid chromatography. The procedure allowed the detection of the enzyme activity expressed by 7.5 μg of liver protein, it was more sensitive and less time-consuming than the spectrophotometric procedure previously used. No significant differences were found between normal controls and patients with primary hyperoxaluria. In an 8-month-infant with primary hyperoxaluria type 1, the enzyme activity was reduced to 16% of the average control values.

1. To determine whether the multiple changes in the blood chemistry profile induced by calcitriol may be conducive to secondary systemic oxalosis we have studied nine patients on regular dialysis treatment under three different regimens: (1) oral calcitriol, 0.25 μg/daily for at least 6 months. (2) off calcitriol, a 1-month withdrawal of the drug, taken as the baseline study period; (3) intravenous calcitriol, 1 μg three times weekly at the end of dialysis, with tests performed at 1 and 3 months from initiation. 2. Serum concentrations were measured pre- and post-dialysis at the end of each study period. The whole dialysate was used for the determination of the overall calcium and oxalate removal by dialysis. The degree of saturation with calcium oxalate mono-hydrate was estimated by a computer program. Serum calcitriol concentrations were also assessed. 3. Total and ionized serum calcium did not change on average, although mild hypercalcaemia developed in some patients on intravenous calcitriol. There was an increase in plasma level of oxalate during both oral and intravenous calcitriol treatment, but this was less pronounced during intravenous therapy. Removal of oxalate by dialysis was also greater in patients on oral calcitriol. 4. These increases were probably originated from intestinal absorption and secondary to hyper-absorption of dietary calcium. Consequently, the degree of saturation with calcium oxalate before dialysis rose during calcitriol treatment, irrespective of the route of administration. 5. These results emphasize that, in addition to soft tissue calcification due to calcium phosphates, ectopic calcium oxalate crystallization must also be viewed as a potential risk associated with long-term administration of calcitriol.

We assessed plasma levels and removal rates of oxalate in 24 patients on chronic peritoneal dialysis (CPD) for oxalosis-unrelated renal failure. The ion-chromatographic (IC) measurements of oxalate in plasma, dialysate, and urine (in seven patients with residual renal function) were used to calculate peritoneal and renal clearances of oxalate. The serum state of saturation with calcium oxalate was calculated by means of a computer-based model system. Patient data were compared with those from 19 healthy individuals. Peritoneal clearance of oxalate was 6.3 +/- 4.7 mL/min, ie, 8% of the normal renal clearance. As a result, both plasma oxalate and calcium oxalate saturation were higher than in controls and did not overlap. Plasma was supersaturated with calcium oxalate in only two of 24 patients (8%). Removal of oxalate by dialysis was related to the amount of fluid infused. Overall removal of oxalate (dialysate plus urine) was similar to 24-hour excretion of normal subjects and was taken as a measure of its generation. Oxalate generation rate was dependent on protein (whole and animal) intake, but not on caloric intake or pyridoxine status. Pyridoxine supplementation, 75 and 300 mg daily for 1 months, was not effective in reducing plasma levels or generation rates of oxalate. Residual renal function had a minor influence on oxalate patterns. We conclude that current programs are adequate to maintain oxalate balance in patients on CPD under basic conditions.

Primary hyperoxaluria type I (PH1) always leads to end-stage renal failure (ESRF) due to deposition of calcium oxalate in the kidney. Regular dialysis therapy (RDT) can not overcome the excess production of oxalate, hence, systemic oxalate deposition occurs. The extent of tissue deposition and the rate at which oxalate accumulates influence the quality of life and survival of the patients. Therefore, an estimate of the oxalate balance needs to be made for patients on RDT. In this study, we suggest a simple model by which some of the main parameters of oxalate turnover can be assessed without using radioactive materials. Levels of oxalate, glycolate, and urea, and degrees of calcium oxalate saturation, were assessed on plasma ultrafiltrates from two patients with PH1, sampled before, at the end of a dialysis session, and over the entire interdialytic interval. In patients with PH1, oxalate increased linearly during the early phases and then the curve flattened at a concentration corresponding to approximately threefold saturation. The initial phase of the relationship was used to estimate generation rate of oxalate. The delayed phase was ascribed to the deposition of newly generated oxalate out of its miscible pool. Conversely, the relationship for glycolate and urea remained linear. This was also different from the values obtained in four patients with oxalosis-unrelated ESRF, whose oxalate levels increased linearly over the entire interdialytic interval. In the two patients with PH1, the overall oxalate generation was assessed at 4 to 7 mmol/d. The difference between generation and dialysis removal indicated that tissue deposition was greater than 50 δmol/kg body weight/d. Pyridoxine therapy produced some improvement in only one of these patients. On the contrary, all of the patients with oxalosis-unrelated ESRF maintained oxalate balance with the current dialysis schedules. We suggest that this simple model may represent a valuable and reproducible means to routinely perform oxalate balance studies on patients on RDT for PH1.

Glycolate determination detects type I primary hyperoxaluria in dialysis patients. The detection of type I primary hyperoxaluria is based on the finding of exceedingly high oxalate excretion which is associated with increased glycolate excretion. The differential diagnosis of this disease may become a difficult task once end-stage renal disease (ESRD) and anuria have supervened. The various procedures thus far proposed to obviate this circumstance are complex, inaccurate or not reproducible. In this paper we propose the accurate liquid chromatographic determination of glycolate in blood and dialysate as a means to detect type I primary hyperoxaluria in patients on maintenance hemodialysis (RDT). The method is based on the enzymatic conversion of glycolate to glyoxylate coupled with α-keto acid derivitization with phenylhydrazine. The resulting phenyhydrazone is then resolved by high-performance liquid chromatograph (HPLC). With this method, plasma glycolate in 12 healthy controls was 7.8 ± 1.7 μmol/liter, almost twentyfold less than previously reported. Five dialysis patients with high serum oxalate, of whom four with primary hyperoxaluria and one with Crohn's disease and presumed enteric oxalate hyperabsorption, were checked by this method and compared to nine patients with oxalosis-unrelated ESRD. The patients with hyperoxalemia were also evaluated for their response to pyridoxine therapy. The measurement of glycolate in blood drawn prior to and at the end of the dialysis session as well as in the dialysate soundly discriminated the patients with type I hyperoxaluria from all the other dialysis patients. Glycolate measurement was shown to be much more powerful than oxalate in that patients with oxalosis-induced ESRD exhibited an almost two hundred and fiftyfold increase compared to the oxalosis-unrelated patients. There was no overlapping at all irrespective of timing and type of sampling. Glycolate measurement represented a valuable tool to distinguish Crohn's disease related from genetically induced hyperoxalemia and to assess responsiveness to pyridoxine treatment.

A liquid chromatographic procedure for the determination of glycolic acid in plasma is proposed. The system is based on pre-column derivatization of the alpha-keto acid by means of phenylhydrazine, coupled with the enzymatic oxidation of glycolate to glyoxylate. The phenylhydrazone formed is separated by reversed-phase liquid chromatography and detected by UV absorption. The measured within and between-batch CV imprecision was 2.6 and 11.3%, respectively, at 5.68 mumol/l glycolate concentration; the analytical recovery was 102.0 +/- 7.3% and the minimum detectable concentration of glycolate was 0.3 mumol/l. The reference interval for plasma glycolate was 4.51 to 12.20 mumol/l (n = 14). Results of determinations of plasma samples from uremic patients, patients with type I primary hyperoxaluria and patients with chronic renal failure secondary to systemic oxalosis are reported.

We propose using ion chromatography to determine tartrate concentration in urine. A 100-microL sample of urine is diluted and injected into the chromatograph. Tartrate is eluted within 11.5 min as a distinct and well-resolved peak. The sensitivity of the standard procedure (signal-to-noise ratio, 3/1) is 30 mumol/L. The intra-run and interrun coefficients of variation are 2.5% and 4.1%, respectively. Mean analytical recovery of known amounts of added tartrate ranges between 94.2% and 104.0%. We investigated the specificity of the procedure by analyzing urine containing added dicarboxylic acids structurally related to tartrate. The reliability of the procedure makes it suitable for investigating tartrate metabolism, e.g., the potential role of tartrate as an inhibitor of crystallization in calcium nephrolithiasis.

In an attempt to decrease ascorbate interference on the ion-chromatographic determination of urinary oxalate, we compared the effectiveness of four different methods for ascorbate elimination by analyzing a representative urine pool supplemented with successive ascorbate additions. Two of the methods--treatment with ferric ions or boric acid--have been described elsewhere; treatments with nitrites or ascorbate oxidase (EC 1.10.3.3) are investigated here as possible alternatives. Consideration of the main features, advantages, and drawbacks of the four procedures leads us to conclude that boric acid dilution is a good routine method and that pre-incubation with ascorbate oxidase reliably prevents ascorbate interference in assays of urinary oxalate.

The occurrence of chronic renal insufficiency was investigated in 171 patients with severe idiopathic calcium stone disease. Ninety healthy subjects matched for age and sex were used as controls. The patients were thereafter subclassified into two subgroups, assuming a GFR of 80 ml/min/1.73 m2 body surface area as a cut-off value: the normal GFR, 141 patients, and the impaired GFR, 30 patients. The normal GFR group included more males and the patients were younger both at onset and at presentation. In the impaired GFR group the disease lasted longer, but the overall stones and the stone recurrence rate were as high as those of the normal GFR patients. The single stone episodes were more severe in the former group as suggested by the occurrence of more surgery and complications. The GFR level was in part predicted by the age of patients; however, stone disease was shown to induce a clear-cut influence in accelerating the natural worsening of GFR with age. The onset of renal insufficiency causes multiple changes in renal pathophysiology, which result in a sharp decrease in the urine saturation with respect to calcium salts. These changes account for the decrease in the stone recurrence rate in the impaired GFR group. Thus, unless factors independent of or complicating the calcium stone disease supervene, the renal insufficiency of treated patients remains mild and relently progressive.

This new procedure for determining oxalic acid in plasma is based on sample deproteinization with hydrochloric acid and acetonitrile and subsequent ion-chromatographic assay of the neutralized supernate. Sample pretreatment produces very clean samples, which ensures long column life. Mean analytical recovery of oxalate (5.0-10.0 mumol/L) added to plasma samples averaged 98.6 +/- 6.2%; imprecision (CV) was 5.2% (at 2.2 mumol/L) and the detection limit was 0.5 mumol/L at a signal-to-noise ratio of 5:1. Ascorbate to oxalate conversion was < 0.2%, indicating that the procedure is free from ascorbate interference. Plasma oxalate concentrations, measured in samples from 31 healthy persons, ranged from 0.8 to 3.4 mumol/L (mean 1.89, SD 0.75 mumol/L), which agrees with results from indirect radioisotopic dilution methods.

We describe a liquid chromatographic technique to determine L-glycerate in body fluids. The method is based on the derivatisation of the L-glycerate by incubation with lactate dehydrogenase and nicotinamide-adenine dinucleotide in the presence of phenylhydrazine. Oxidation of L-glycerate forms beta-hydroxypyruvate which is converted in turn into the related phenylhydrazone. The UV-absorbing derivative is determined using reversed-phase high performance liquid chromatography. The sensitivity was 5 mumol/l and 50 microliters of sample were required. The imprecision relative standard deviation was 4.5% and the recovery was 96.5 +/- 6.8% for L-glycerate in plasma. L-Glycerate concentrations in urine and plasma were less than 5 mumol/l in both normal individuals and patients with glycolic aciduria. In a patient with systemic oxalosis and normal plasma glycolate, plasma L-glyceric acid was 887 mumol/l.

To differentiate hyperoxaluria syndromes we measured plasma and urine glycolate by a novel high performance liquid chromatographic procedure. Mean glycolate level was 7.9 +/- 2.4 mumol./l. in plasma and 422 +/- 137 mumol./24 hours in urine from 19 control subjects. Renal clearance was about 50% the glomerular filtration rate irrespective of the underlying disease. There was close correlation between glycolate and oxalate in plasma. Plasma glycolate was normal in all but 8 patients who had primary hyperoxaluria 1. Plasma assay detected the disease more efficiently than urine assay. Pyridoxine decreased oxalate biosynthesis in 2 of the 4 patients treated with it and glycolate assay confirmed this behavior. Glycolate excretion was significantly high in 3 of 8 patients of primary hyperoxaluria 1 patients. Idiopathic stone formers had mild increases in glycolate excretion but this was not related with oxalate excretion. Glycolate levels were normal in 5 patients with enteric hyperoxaluria. We conclude that glycolate assay is essential for identifying patients with primary hyperoxaluria 1 and may represent a valuable tool for differentiating hyperoxaluria.

We examine the suitability of a rapid and sensitive liquid chromatographic technique to determine L-alanine:glyoxylate aminotransferase (AGT) activity in human liver. Homogenised tissue was incubated for 30 min in the presence of substrates and the generated pyruvate was converted into the corresponding phenylhydrazone which was determined using reversed-phase high-performance liquid chromatography (HPLC). The procedure allowed the detection of the enzyme activity expressed by 10 micrograms of liver protein and was rapid enough resulting more sensitive and less time-consuming than the previous colorimetric one. We found that AGT activity in two hyperoxaluria type 1 patients was reduced as compared with controls. Also, cirrhotic patients had very low enzyme activities, even in the absence of detectable disorders of oxalate metabolism and this was ascribed to abnormal liver morphology. This may represent a misleading drawback if diagnosis of type 1 primary hyperoxaluria (PH1) uniquely relies on AGT assay.

Regular dialysis treatment (RDT) does not obviate hyperoxalemia of chronic renal failure (CRF). However, there is emerging evidence suggesting that current dialysis prescription is not always associated to progressive oxalate accumulation. In view of the controversy still concerning this issue, we have investigated on plasma profiles and dialysis kinetics of oxalate in patients on RDT. Oxalate was determined by ion chromatography on serum ultrafiltrates and on the whole dialyzate in 23 stable patients on RDT for end-stage renal failure unrelated to primary hyperoxaluria. Nine patients were on traditional hemodialysis (HD) and 14 on soft hemodiafiltration (HDF). Dialysis prescription was set so as to obtain similar KT/V of urea. Mean dialyzer clearance of oxalate (KdOx) was calculated by standard procedures and was compared to urea (KdUrea) and creatinine (KdCr) clearances. Oxalate removal was measured on the whole spent dialyzate. Distribution volume of oxalate (VOx) was estimated by assuming a single-pool model and was used to estimate the oxalate appearance rate (OxAR). Plasma profiles showed that dialysis patients were virtually always hyperoxalemic. However, the threshold of supersaturation for calcium oxalate was exceeded in only 13 of 138 (9.4%) assayed ultrafiltrates, 13% on HD and 7.1% on HDF. Dialysis reduced plasma oxalate by more than 60%. There was a postdialysis oxalate rebound averaging 9.6% at 30 min from the end of dialysis. Plasma oxalate predialysis was independent of sex, age and time on dialysis. KdOx was mildly higher on HDF than on HD, and was lower than both KdUrea and KdCr, irrespective of the dialysis technique.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Regular dialysis treatment is reported to remove inorganic sulphate, but not to restore its level to normal. To evaluate the adequacy of modern dialysis techniques in maintaining the sulphate balance, intra- and inter-dialysis plasma profiles and removal rates of sulphate were studied in 20 stable patients on maintenance haemodialysis. The influence of sulphate levels on the distribution of calcium-complex species was also investigated. 2. Sulphate was determined by ion-exchange chromatography of both serum ultrafiltrates, taken at the start of, during, at the end of, and at 24 h and 48 h after a dialysis session, and whole diffusate collections. Dialyser clearances of sulphate were assessed by two independent procedures and compared with those of urea and creatinine, on two different methods of dialysis, i.e. traditional haemodialysis with Cuprophan hollow fibre filters, and haemodiafiltration with high-flux Polysulphone or polyacrylonitrile dialysers. Concentrations of the main serum ions were determined before and after dialysis and used to solve a multiple mass balance equation system by which concentrations of the calcium-complex species were calculated. 3. Before dialysis, sulphate levels were eight times those determined in 17 control subjects and remained higher than normal at the end of dialysis. These changes were independent of the dialysis procedure. There was a close correlation between serum levels of sulphate and creatinine. Dialyser clearances of sulphate were comparable with those of creatinine, but lower than those of urea. Clearances of all solutes were higher on haemodiafiltration. 4. The mean removal of sulphate during a single session was about 30 mmol; the estimated removal rate averaged 15 mmol/day and was closely related to the protein catabolic rate as derived by urea kinetic modelling. Removal rates were slightly lower than rates of sulphate excretion in 40 control subjects. Because serum sulphate levels were quite stable over time this decrease was accounted for by a reduction in the net generation of sulphate, due to either altered catabolism of sulphur-containing amino acids or reduced intakes of animal protein. 5. The distribution of calcium-complex species demonstrated that the calcium-sulphate complex concentration in pre-dialysis samples was similar to that of calcium-phosphate complex and both were markedly increased as compared with normal subjects. Dialysis minimized but did not cancel out these abnormalities, which were responsible for significant decreases in free calcium concentration. 6. It is concluded that, although dialysis efficiently removes newly generated inorganic sulphate, it does not prevent chronic increases in this anion. Inadequate control of plasma sulphate levels by dialysis or through the diet may adversely affect the clinical state of uraemic patients and induce pervasive changes in calcium homoeostasis.

1. The serum oxalate concentration rises in chronic renal failure and it is only partially eliminated by regular dialysis treatment. However, the recent literature is not conclusive on whether progressive oxalate retention and secondary oxalosis should be expected in patients on regular dialysis treatment. 2. To further investigate this, we have estimated the state of saturation with respect to calcium oxalate mono-hydrate in plasma ultrafiltrates from 28 patients on maintenance haemodialysis and eight healthy control subjects, matched for sex and age. Five patients had type I primary hyperoxaluria and histologically proven oxalosis, whereas 23 had oxalosis-unrelated renal diseases. Dialysis efficiency was quantified as the KdTd/V of urea. Samples were obtained from each patient before, immediately after and 48 h after a dialysis session. Fasting samples were obtained from the control subjects. Oxalate was determined in both plasma ultrafiltrates and the whole dialysate by ion-exchange chromatography, after a non-delayed and [14C]oxalate-recovery-controlled procedure. The state of saturation with calcium oxalate monohydrate was estimated by means of a computer system which solved the interactions among 45 complex species. 3. The fasting plasma oxalate concentration (means ± sd) in ultrafiltrates from healthy subjects was 3.8 ± 1.5 (range 1.4–5.8) μmol/l, and the state of saturation with calcium oxalate monohydrate was 0.096 ± 0.04. The 23 patients with oxalosis-unrelated chronic renal failure had a pre-dialysis plasma oxalate concentration of 49.8 ± 14.0 μmol/l, which yielded a state of saturation with calcium oxalate monohydrate of 1.0 ± 0.3; dialysis produced a steep decrease in the state of saturation with calcium oxalate monohydrate and the samples remained undersaturated at 48 h from the end of the session. The pre-dialysis oxalate concentration in plasma ultrafiltrates from patients with primary oxalosis was 170 ± 21 μmol/l, so as to exceed saturation by more than threefold. The samples remained above saturation even at the end of dialysis. 4. In 116 ultrafiltrates the state of saturation with calcium oxalate monohydrate was closely dependent on the plasma oxalate concentration but not on the plasma calcium concentration. The pre-dialysis state of saturation with calcium oxalate monohydrate was poorly influenced by the residual renal function and was independent of the sex, age, body weight or time on dialysis. 5. The results of the present study suggest that, unless chronic renal failure is due to primary hyperoxaluria, the extracellular body fluid of patients on current dialysis is often undersaturated with calcium oxalate and this is inconsistent with progressive oxalate accumulation and secondary systemic oxalosis. However, since some tissues may generate or selectively accumulate oxalate, local formation of crystalline deposits may still occur on regular haemodialysis.

Citrate is a relevant component of the inhibitory potential of the urine environment. Its excretion and renal handling have been widely studied in subjects with normal renal function, but little is known about changes induced by chronic renal insufficiency. We have investigated renal handling of citrate in 50 patients with different degrees of renal insufficiency as compared to 30 healthy subjects with normal renal function. Among patients 34 were defined as having mild renal insufficiency based on a GFR of 80 through 40 ml/min/1.73 m2 BSA, while 16 had moderate-to-severe renal failure, defined by a GFR ranging from 40 to 20 ml/min/1.73 m2 BSA. Serum citrate increased in mild renal insufficiency, while it tended to be restored to normal values at more advanced renal failure. There was a stepwise decrease in the filtered load of citrate as GFR decreased, while its renal clearance was significantly reduced only at higher degrees of renal failure. This behavior was due to an increase in the fractional excretion of citrate which was inversely related to the decrease in GFR (p = 0.015). These data suggest that serum citrate levels and excretion are governed by renal mechanisms at mild degrees of renal insufficiency; in these conditions citrate is shown to behave conformly to other poorly reabsorbable anions such as sulfate. At more advanced renal failure the ensuing metabolic acidosis plays a crucial role as a regulatory factor of both serum concentration and renal handling of citrate, by increasing cellular uptake and metabolism as well as tubular reabsorption of this anion.(ABSTRACT TRUNCATED AT 250 WORDS)

An ion chromatographic procedure for the determination of plasma oxalate is proposed, in which the ultrafiltered sample is injected into an ion-chromatographic system. Sample processing appears effective in avoiding spontaneous oxalogenesis. Sensitivity (down to 1.0 mumol/l) allows determinations in normal and pathological samples; recoveries from plasma ultrafiltration are 94.6 +/- 11.7%. Protein binding was investigated and precautions to improve recoveries from plasma ultrafiltration are proposed. The technique is simple to perform from healthy controls averaged 6.75 +/- 2.62 mumols/l (mean +/- S.D. n = 18); samples from patients with primary hyperoxaluria and chronic renal failure undergoing regular dialysis were also analysed and some of the data obtained are reported and discussed.

CAPD with an amino acid dialysis solution: A long-term, cross-over study. This prospective cross-over study was undertaken to evaluate the safety and efficacy of a 1% amino acid dialysis solution on the nutritional and metabolic changes, plasma amino acid profiles and peritoneal membrane function of patients on CAPD. Six CAPD patients had one exchange a day with two liters of this solution over a six month period. Every month there was a medical examination, anthropometric measurements and dietary inquiry were made, blood biochemistry tests were done. Every three months renal function, peritoneal function, aminograms of plasma and dialysate and nitrogen balance were determined. Data were compared with those obtained one month prior to and three months after withdrawal of amino acid administration. Nitrogen balance, which was negative (-1.3 g/day) became positive (+3.1 g/day). Patients who were already overweight increased in weight, both in fat and lean mass. Plasma cholesterol and triglycerides significantly decreased and the amino acid profile moved towards normal; plasma urea levels increased and pH and bicarbonate decreased slightly but significantly (P < 0.05). Plasma protein concentrations did not change. All the above parameters turned towards basal values when amino acids were discontinued. We conclude that amino acids can be used as osmotic agents for CAPD since they do not cause toxic effects or impair peritoneal membrane function. Moreover, they can help the nutritional status, provided that an increase in weight is prevented and the slight worsening of systemic acidosis is corrected.

A high-performance liquid chromatographic (HPLC) method for the determination of urinary glyoxylic acid is proposed. The system is based on the precolumn derivatization of alpha-keto acids by means of phenylhydrazine, separation of the phenylhydrazone formed by HPLC and spectrophotometric detection at 324 nm. The method is precise and allows the determination of 0.5 mumol/l glyoxylate. The poor stability of glyoxylate under all conventional preservation conditions requires the analysis to be carried out as soon as possible after urine collection. Results of determinations on urine samples from healthy controls and from patients with idiopathic calcium stone disease and type I primary hyperoxaluria are reported.

1. Seventeen healthy controls and 63 patients with idiopathic calcium stone disease of the urinary tract were investigated for urinary calcium and oxalate excretion and for [14C]oxalate intestinal absorption. 2. Under comparable controlled dietary intake a significant increase in calcium excretion was found in patients with stone disease. Oxalate excretion and [14C]oxalate intestinal absorption were mildly but not significantly increased. When patients with stone disease were subdivided into normocalciuric and hypercalciuric subjects, oxalate excretion and [14C]oxalate absorption were significantly increased in the latter. There was a significant direct relationship between calcium excretion and both oxalate excretion and [14C]oxalate absorption. 3. [14C]Oxalate absorption increased significantly in 22 stone-formers when dietary calcium was changed from normal to low. 4. The kinetics of [14C]oxalate intestinal absorption showed that the main difference between normocalciuric and hypercalciuric subjects occurred within the first 6 h after the oxalate-labelled meal. 5. These results confirm that mild hyperoxaluria is a frequent feature of idiopathic calcium stone disease even when patients and controls are studied under controlled dietary conditions. Our data are consistent with the hypothesis that hyperoxaluria is secondary to calcium hyperabsorption and is upper intestinal in origin.

Bony content of oxalate in patients with primary hyperoxaluria or oxalosis-unrelated renal failure. Oxalate retention occurs in end-stage renal failure. Regular dialysis treatment does not prevent progressive accumulation of oxalate in cases of ESRF due to primary hyperoxaluria (PH), whereas such accumulation seldom seems to occur in oxalosis-unrelated ESRF. To elucidate this issue we have measured the bony content of oxalate on biopsies of the iliac crest taken from 32 uremic patients, 7 of them with ESRF associated with PH1 (6 cases) or PH2 (1 case). Ten subjects with normal renal function and no evidence of metabolic bone disease were taken as controls. Only trace amounts levels of oxalate were detected in normal subjects and oxalate to phosphate ratio was below 3:10,000. Non-PH dialyzed patients exhibited fivefold increases in oxalate levels, which rose to 5.1 ± 3.6 µmol/g bony tissue. Calcium oxalate was estimated to represent 0.18% of the hydroxyapatite content of bone. Oxalate amounts were neither related to pre-dialysis plasma levels of oxalate, nor with duration of dialysis treatment, suggesting that accumulation was not progressive disorder. Oxalate levels were slightly higher in patients with a low turnover osteodystrophy compared to those with a high turnover pattern. Dialyzed patients with PH had remarkable increases in oxalate levels, which ranged between 14.8 and 907 µmol/g bony tissue. Oxalate deposition appeared to be progressive in that oxalate levels were significantly related to time on dialysis. In three patients calcium oxalate was a significant fraction of the mineralized bone. The occurrence of calcium oxalate crystals affected the histomorphometric patterns, that were featured by an increase in resorptive areas and a decrease in bone formation rate. We suggest that oxalate measurement in bony tissue gives reliable information of the status of oxalate burden in dialyzed patients. In this study oxalate deposition in bone has emerged as a non-progressive and meaningless event in patients with oxalosis-unrelated ESRF. Conversely, in patients with primary hyperoxaluria on maintenance hemodialysis, it evolves following a pattern so relentless that such patients should clearly be considered for organ transplantation as soon as possible.

A high-performance liquid chromatographic method for the determination of urinary glycolic acid is proposed, based on pre-column derivatization with phenylhydrazine coupled with the enzymatic oxidation of glycolate to glyoxylate. The phenylhydrazone formed is separated by liquid chromatography and detected at 324 nm. The minimum detectable concentration of glycolate was 10.0 mumol/l. The recovery of glycolate added to urine averaged 96.1%. The day-to-day coefficients of variation calculated by analysis of two urine samples with normal and high glycolate contents were 4.6 and 7.5%, respectively. Results of analyses of urine samples from healthy persons, idiopathic calcium stone formers and Type I primary hyperoxaluria patients are reported.

A high-performance liquid chromatographic method for the determination of carbonyl compounds, namely aldehydes, ketones and keto acids in urine, has been developed. Pre-column derivatization with 2,4-dinitrophenylhydrazine offers sufficient sensitivity for the determination of glyoxylic acid in urine with a detection limit of 0.5 mg/l. The separation is performed on a C18 10-micron column and with an acetonitrile-aqueous buffer mobile phase, which also allows the resolution of the syn and anti geometric isomers. Matrix effects, precision, accuracy, limits of detection and structural selectivity of the method are discussed.