Renal stone analysis: why and how?

Upper urinary tract stone disease is widespread in the developed world. On both clinical and economic grounds it is now accepted that evidence-based medical intervention is the only approach likely to make a significant impact on the incidence, and more importantly, the recurrence rates of this disease. Targeted medical prophylaxis requires reliable information on stone type which, when combined with relevant blood and urine analyses, allows identification of treatable risk factors. Data from an external quality assurance scheme indicate that stone analysis is poorly performed in many laboratories, and it is probable that this results in ill-informed patterns of investigation, inappropriate therapy, missed diagnoses of rarer causative disorders and wasteful further investigation of 'non-renal' stone artefacts. Renal stone analysis is a specialist investigation requiring appropriate analytical and interpretative expertise if the information is to be used to enhance patient care. For those laboratories not able to offer this, for whatever reason, referral is the only defensible approach to service provision. The methods currently employed in many departments have no place in modern clinical biochemistry practice.

Effects of Tamm-Horsfall protein with normal and reduced sialic acid content upon the crystallization of calcium phosphate and calcium oxalate in human urine.

OBJECTIVE: To examine the effects of Tamm-Horsfall protein (THP) of normal and low sialic acid content on urinary crystallization, and establish whether there are changes conducive to the formation of kidney stones. MATERIALS AND METHODS: Purified samples of THP were recovered from the urine of non-stone forming individuals. A portion of each THP sample was treated with the enzyme neuraminidase to yield the low sialic acid form of the protein. The two forms of THP were added separately to ultrafiltered urine and crystallization was then induced in the urine by evaporation at 37 degrees C. Two types of experiment were then conducted with the crystals that formed; the rate at which the resulting calcium phosphate or calcium oxalate crystals sedimented in the evaporated urine was determined and the proportion of these crystals and protein which was retained when the urine was passed through a 75 microns sieve was measured. RESULTS: Calcium phosphate and calcium oxalate crystals remained in stable colloidal suspension in ultrafiltered urine when in the presence of normal THP; these suspensions passed freely through the 75 microns sieves. When crystals formed in the presence of low sialic acid THP, the sedimentation was rapid and the crystals were readily retained with protein on the sieves. CONCLUSIONS: These results indicate that whilst normal THP inhibits urinary crystal aggregation, the properties of the low sialic acid form are consistent with the promotion of crystal aggregation and hence stone formation.

A semiautomated alanine:glyoxylate aminotransferase assay for the tissue diagnosis of primary hyperoxaluria type 1.

We have developed a sensitive assay for the measurement of alanine:glyoxylate aminotransferase (EC 2.6.1.44) activity in human liver. The assay is partly automated, and takes into consideration the sensitivity of the reaction to pH and to glyoxylate concentration. It is less subject to interference from other enzymes utilizing glyoxylate and to chemical interference from glyoxylate itself and can therefore be used without correction for cross-over by glutamate:glyoxylate aminotranferase (EC 2.6.1.4). The assay allows clear discrimination between normal and affected livers and is sufficiently sensitive to measure enzyme activity in fetal liver samples. Enzyme activity ranged from 17.9 to 38.5 mumol/h/mg protein in control livers (n = 9) and 0.8 to 9.5 mumol/h/mg protein in 30 of 39 hyperoxaluric patients studied. Normal alanine:glyoxylate aminotransferase activity (from 22.8 to 45.5 mumol/h/mg protein) allowed exclusion of primary hyperoxaluria type 1 in the other nine hyperoxaluric patients.

The inhibitory activity of some citrate analogues upon calcium crystalluria: observations using an improved urine evaporation technique.

The ability of three compounds, all similar in chemical structure to citric acid, to decrease calcium crystalluria has been measured. The measurements were made in normal human urine at 37 degrees C and compared with the crystal-decreasing power of citric acid when measured in the same way and in the same urine samples. One of the compounds tested, phosphocitric acid, was more potent than citric acid in inhibiting calcium oxalate crystal precipitation. At higher concentrations it also proved more effective against calcium phosphate. A urine evaporation method was used to carry out the crystal inhibition tests after modification to improve its precision.

Rapid computer-assisted infrared analysis of urinary calculi using photoacoustic detection.

The application of commercial spectrum-analysing software to quantitative analysis of urinary stones by Fourier transform infrared spectrophotometry is described. The infrared technique is straightforward in comparison with other stone analysis procedures of similar scope and affords significant time savings. The use of partial least squares regression in the analysis program enables better quantitation of stone components than has been hitherto possible using infrared methods. All the principal and many less common stone constituents can be detected and measured. Photoacoustic detection was employed, thus enabling non-destructive analysis with minimal sample preparation. A comparison is made between the infrared procedure and the hybrid thermogravimetric plus "wet" chemistry technique, which it has superseded for routine urinary stone analysis in the author's department.

Risk factors for calculus formation in patients with renal transplants.

OBJECTIVE: To investigate the risk factors for stone formation in patients with functioning renal transplants in whom renal calculi develop. PATIENTS AND METHODS: Renal calculi developed in six of 178 patients with functioning renal transplants under current review, an incidence of 3%. Risk factors for stone formation were investigated in five of these patients and compared with a randomly selected control group of 41 transplant patients with no stone problems. RESULTS: Patients with transplant calculi typically passed smaller volumes of significantly more concentrated and alkaline urine with greater urinary excretion of uric acid (P < 0.05). Urine calcium excretion was also increased. Crystalluria was present in three of five stone formers compared with two of 25 controls. Overall, metabolic abnormalities included hypocitraturia (75%), hyperparathyroidism (36%), hypophosphataemia (24%) and hypercalcaemia (10%). Urinary infection was common (50%) and urinary output of magnesium and phosphate was at the lower end of normal for all patients. CONCLUSION: These results suggest a multifactorial aetiology for stone formation in renal transplant recipients. Approaches to prevention and management are discussed.

Chemical analysis of post-lithotripsy stone fragments: a critical evaluation.

A scheme for the chemical microanalysis of renal stone fragments recovered from urine voided immediately after lithotripsy has been developed and evaluated. The analytical procedure includes assay of calcium, magnesium, phosphate, oxalate and urate and has been applied to 78 such urine samples. Problems relating to co-existing crystalluria and blood and urine contaminants have been recognised and overcome. However, significant loss of all stone components due to fragment dissolution in urine prior to recovery was found to occur and was investigated. The distribution of stone components found in these analyses was similar to that seen in previous surveys of intact stones.

Ammonia levels in paediatric ureterosigmoidostomy patients: a screen for hyperammonaemia?

Hyperammonaemia in the urological patient is a rare and potentially grave condition. It has been reported most frequently in association with ureterosigmoidostomy, where clinical neurological symptoms have developed abruptly in association with markedly elevated plasma ammonia levels. The purpose of this study was to determine whether ureterosigmoidostomy patients might have subclinically elevated plasma ammonia levels, which would put them at risk of subsequently developing hyperammonaemic encephalopathy. Both urine and plasma ammonia levels were assayed in 10 asymptomatic paediatric urological patients with ureterosigmoidostomy. Ten paediatric colocystoplasty patients served as controls. Urine pH and urine ammonia levels were significantly higher in the ureterosigmoidostomy group. There was no significant difference in plasma ammonia levels between ureterosigmoidostomy and colocystoplasty patients. In none of the patients was the plasma ammonia level elevated, but 1 ureterosigmoidostomy patient had an exceedingly high urine ammonia level. It was concluded that an annual serum ammonia level in an asymptomatic ureterosigmoidostomy patient is probably not a valuable screen for subclinical hyperammonaemia.

Failure of allopurinol to modify urinary composition in enteric hyperoxaluria.

Conventional treatment of enteric hyperoxaluria (EHO) consists of dietary restriction of oxalate and fat and correction of its underlying cause whenever possible. Recent work suggests that allopurinol reduces the incidence of urolithiasis and the urinary excretion of both oxalate and uric acid in patients without intestinal disease. We have assessed the effect of allopurinol, 300 mg daily for 2 weeks, on urine biochemistry in patients with EHO due to small bowel Crohn's disease and/or resections. Compliance with treatment was confirmed by a fall in plasma uric acid in every patient. Allopurinol failed to alter 24 h urinary oxalate excretion or oxalate concentration. There were also no significant changes in the urinary excretion of glycollate (like oxalate, a breakdown product of glyoxylate), citrate, magnesium or calcium, each of which was at the lower end of the normal range before and during treatment with allopurinol. It appears unlikely that allopurinol will prove useful in the prevention of urolithiasis in patients with EHO.

Renal abnormalities in ankylosing spondylitis.

The incidence of renal abnormalities is increased in patients with ankylosing spondylitis (AS). Possible mechanisms include the effects of nonsteroidal anti-inflammatory drugs (NSAIDs), an increased incidence of glomerulonephritis and the deposition of amyloid. We assessed renal function in 51 patients with AS randomly selected from those attending routine rheumatology clinics. Five patients were found to have a definite renal abnormality and three of them underwent renal biopsy. These showed one case each of IgA glomerulonephritis, focal segmental glomerulosclerosis and nonspecific tubulo-interstitial damage. A sixth patient had recurrent haematuria and borderline renal functional impairment but refused further investigation. The urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) was elevated in four patients; two had other biochemical evidence of renal damage while the other two patients appeared normal, although they had both received spinal irradiation in the past. The finding of a significant renal abnormality in 10% of AS patients suggests that evidence of renal involvement should be actively sought in this disease.

Serum and tissue tumour markers in seminomas.

The serum expression of the tumour markers hydroxybutyric dehydrogenase (HBD), beta human chorionic gonadotrophin (beta HCG), alphafetoprotein (alpha FP) and placental alkaline phosphatase (PLAP) has been assessed in a consecutive series of 50 patients with pure seminoma. In pre-orchiectomy sera from 15 patients with stage I disease, HBD was elevated in 5, beta HCG in 3, alpha FP in 1 and PLAP in 1 (of 3 only). In 27 patients with stage 2 or 3 disease, prior to chemotherapy, serum HBD was elevated in 19, beta HCG in 11, alpha FP in 2 and PLAP in 10 (of 18). The presence of beta HCG was investigated immunocytochemically in primary tumour tissue from 39 patients. It was demonstrated in 6 of 21 tumours from patients with stage I disease and 5 of 18 with stage 2 or 3 disease.

Assay of microalbuminuria using gel electroimmunoassay.

The possibility of using electroimmunoassay as a technique for assessing microalbuminuria in the diabetic population has been studied. The method was found to be precise (given inter-batch coefficients of variation of 5.7% and 5.8% at levels of 16 mg/l and 23 mg/l respectively), showed adequate sensitivity, and produced results which correlated well (r = 0.971) with these obtained from a routine radioimmunoassay procedure. It is concluded that electroimmunoassay provides a reliable alternative to more sophisticated techniques in the non-specialized laboratory dealing with only moderate numbers of specimens.

Radioimmunoassay for prostatic acid phosphatase in early prostatic carcinoma.

A radioimmunoassay procedure has been used to measure prostatic acid phosphatase in the serum of 46 patients with intracapsular carcinoma of the prostate. The results obtained did not differ significantly from those obtained in a control group of similar size. It is concluded that the radioimmunoassay procedure for measurement of prostatic acid phosphatase has no advantage over enzyme activity measurements for the detection of early prostatic carcinoma.

Absorption of glucose from urinary conduits in diabetics and non-diabetics.

The ability of urinary conduits to absorb glucose was investigated. A solution containing 1% glucose and the inert marker phenol red was put into conduits in diabetic and non-diabetic patients. Samples were withdrawn at intervals for analysis and the fall in concentrations plotted against time. The loops in the patients without diabetes did not absorb glucose, but glucose was absorbed in one of the three diabetics. Ileal loops in patients with diabetes may absorb urinary glucose. This should be checked in any diabetic with urinary diversion before advice is given on long term management. Routine testing of conduit urine for glucose may not be an adequate screen for diabetes in patients with urinary diversions.

A study of glycosaminoglycan excretion in normal and stone-forming subjects using a modified cetylpyridinium chloride technique.

Precipitation with cetylpyridinium chloride followed by hexuronic acid assay has been used to study glycosaminoglycan excretion in normal subjects and calcium stone formers. It was found necessary to concentrate dilute urines prior to assay to achieve satisfactory precipitation of the glycosaminoglycans. No significant differences in daily glycosaminoglycan excretion were detected between normal and stone-forming subjects.

Uromucoid excretion in normal subjects, calcium stone formers and in patients with chronic renal failure.

Using an electroimmunoassay technique for uromucoid in urine, the excretion of this protein has been studied in normal subjects, calcium stone formers and in patients with chronic renal failure. In the normal subjects there was no significant difference in daily excretion between males and females, but a positive correlation with urine volume was demonstrated for this group. No significant difference in daily uromucoid excretion was found between normal and stone forming subjects. In the presence of chronic renal failure uromucoid excretion was found to be reduced and correlated with overall renal function as assessed by creatinine clearance.