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Biomedical subjects

W G Robertson

Publications and source records attributed to W G Robertson.

14 recordsLinked to original sources
PubMed1979

Influence of urine on "in vitro" crystallization rate of calcium oxalate: determination of inhibitory activity by a [14C]oxalate technique.

A simple radiochemical method is proposed for the in vitro assay of the inhibitory activity of urine with respect to calcium oxalate crystal growth using [14C]oxalate as a tracer. The method shows an improved sensitivity over existing methods and indicates that citrate, pyrophosphate and chondroitin sulphate are active inhibitors of calcium oxalate crystal growth down to concentrations of 10(-5), 10(-7) and 10(-10) mol/l respectively. The inhibitory activity in the urines of 12 recurrent calcium stone-formers was significantly lower than in the urines of matched control subjects (P less than 0.01), confirming the clinical usefulness of the test.

Calcium Oxalate↗
PubMed1979

The effect of high animal protein intake on the risk of calcium stone-formation in the urinary tract.

1. Studies were carried out on six normal male subjects to determine the short-term effect of increasing the dietary consumption of animal protein on the urinary risk factors for stone-formation, namely, volume, pH, calcium oxalate, uric acid and glycosaminoglycans. 2. An increase of 34 g/day of animal protein in the diet significantly increased urinary calcium (23%) and oxalate (24%). Total urinary nitrogen increased by an average of 368 mmol/day. The accompanying increase in dietary purine (11 mmol of purine nitrogen/day) caused a 48% increase in the excretion of uric acid. 3. The overall relative probability of forming stones, calculated from a combination of the risk factors, was markedly increased (250%) throughout the period of high animal protein ingestion.

Adult↗
PubMed1979

Should recurrent calcium oxalate stone formers become vegetarians?

The hypothesis that the incidence of calcium stone disease is related to the consumption of animal protein has been examined. Within the male population, recurrent idiopathic stone formers consumed more animal protein than did normal subjects. Single stone formers had animal protein intakes intermediate between those of normal men and those of recurrent stone formers. A high animal protein intake caused a significant increase in the urinary excretion of calcium, oxalate and uric acid, 3 of the 6 main urinary risk factors for calcium stone formation. The overall relative probability of forming stones, calculated from the combination of the 6 main urinary risk factors, was markedly increased by a high animal protein diet. Conversely, a low animal protein intake, such as taken by vegetarians, was associated with a low excretion of calcium, oxalate and uric acid and a low relative probability of forming stones.

Calcium↗
PubMed1979

Calcium measurements in serum and plasma--total and ionized.

This article will review the methods currently employed for measuring the concentrations of total and ionized calcium in serum or plasma. As far as total calcium is concerned, various techniques such as atomic absorption spectrometry, spectrophotometry, fluorometry, complexometric titration, and flame photometry will be described and compared. Particular emphasis will be given to the accuracy and precision of each technique. Possible sources of error and interfering agents will be identified and the various procedures for the taking and handling of blood samples evaluated. Inter-laboratory variation in the measurement of calcium will be studied. An assessment will be made of a new reference method for measuring total calcium in serum using isotope-dilution mass spectrometry. The usefulness of the total calcium measurement in clinical medicine will be briefly discussed. Within the last decade the refinement of spectrophotometric techniques and the improvements in ion-selective electrode technology have revolutionized the measurement of ionized calcium in serum, such that it may now be possible to replace total calcium measurements with ionized calcium measurements on a routine basis. The various techniques currently in use for measuring ionized calcium will be described and evaluated. Particular attention will be paid to the preparation of standards, the procedures for taking blood samples, and the handling of the samples prior to and during measurement. An assessment of the relative value of measuring total and ionized calcium will be presented.

Calcium↗
PubMed1979

Urinary tract stone disease.

Patients suffering from urinary stone are traditionally referred to a surgeon. Most are investigated only as far as establishing the site of the stone and its effect on renal function. Although a number of patients may require surgery, the majority pass the stone spontaneously and are discharged within a few days. If the patient has a recurrence, as most eventually have, it is not routine practice to establish the type of stone, screen for underlying disease, identify the urinary abnormalities or to institute preventive medical treatment. Although it was considered that surgery itself had something to offer in reducing the recurrence rate this is no longer generally held except in infected stone disease. Nevertheless it is still uncommon to involve a physician, and in particular a nephrologist, in the investigation and management of urinary stone-formers. Urinary stone disease still remains, to a large extent, outside the field of nephrology.

Bacterial Infections↗
PubMed1978

Risk factors in calcium stone disease of the urinary tract.

The concept that calcium stone formation may be explained on the basis of a number of risk factors is developed. The main risk factors involved are shown to be calcium, oxalate, pH, acid mucopolysaccharides and uric acid. A method is described for calculating and combining the individual risk factors into a measure of the "relative probability" of forming stones (PSF). PSF values are generally lower in normal subjects than in stone-formers. Amongst the normals, PSF values are lower in children and women than in men. Recurrent stone-formers have the highest PSF values and these correlate well with the severity of the diseases as defined by the stone episode rate of the patient. Single stone-formers have PSF values intermediate between those of normal men and those of recurrent stone-formers.

Adult↗
PubMed1977

Seasonal variations in the composition of urine from normal subjects: a longitudinal study.

The volume, pH and composition of 24-h urine samples, collected by 13 healthy male adults, were followed over a period of one year. Significant and systematic variations in urine pH, calcium, phosphate, oxalate, uric acid, potassium and magnesium were observed. A significant but non-sinusoidal variation in sodium excretion was found but there were no significant changes in urinary volume, creatinine or hydroxyproline. Many of the observed changes could be attributed to variations in the pattern of food consumption throughout the year but calcium, phosphate and oxalate were exceptions in that seasonal variations in these parameters appeared to be due to the effects of sunlight (or vitamin D) rather than to the diet.

Adult↗
PubMed1976

Saturation-inhibition index as a measure of the risk of calcium oxalate stone formation in the urinary tract.

Studies were carried out on multiple urine samples from eight patients with recurrent idiopathic calcium oxalate stone formation and eight normal persons to define an index of the risk of forming calcium oxalate stones. Under the same conditions of dietary and fluid intake the urine samples of the patients with stone formation were more supersaturated with calcium oxalate (P less than 0.001) and had lower concentrations of protective inhibitors of crystallization (P less than 0.001) than those of the controls. However, the best separation between the groups was defined by a discriminant line relating inhibitory activity and urine saturation. A measure of the risk of forming large crystals, the saturation-inhibition index, was defined as the distance of each urine from the discriminant line. The patients with stone formation had a significantly higher mean saturation-inhibition index than the controls (P less than 0.001). Both the percentage of large calcium oxalate crystals excreted (P less than 0.001) and the stone episode rate (P less than 0.005) were significantly correlated with the saturation-inhibition index.

Calcium↗
PubMed1976

Measurement of ionised calcium in body fluids-a review.

This paper reviews the techniques available to the clinical biochemist for measuring ionised calcium concentrations in biological fluids with particular reference to serum. At present ionised calcium may be measured colorimetrically, using tetramethyl murexide, or potentiometrically, using a calcium ion-selective electrode. These techniques compare favourably in terms of precision with existing methods for measuring total calcium. Advantages of measuring ionised calcium in preference to total calcium are (a) that there is no effect of venous occlusion or change of posture on the ionised fraction of the effect on total calcium, (b) that ionised calcium is the physiologically active form of the element, and (c) that the ionised calcium concentration is a more reliable indicator of the calcium status of patients in certain clinical conditions. The main problem in the measurement of ionised calcium is the marked dependence of the ionised fraction of the pH of the sample. Extreme care must be taken to avoid loss of CO2 or build-up of acid during the handling of the blood sample.

Blood Specimen Collection↗
PubMed1975

Seasonal variations in the composition of urine in relation to calcium stone-formation.

1. A retrospective cross-sectional study was carried out on data derived from single 24 h urine collections from 246 male idiopathic calcium stone-formers. 2. The daily urine volume and pH and the exretions of calcium, oxalate, phosphate, creatinine and magnesium were related to the time of year when the urine was collected, and the saturation of urine with calcium oxalate and octocalcium phosphate calculated for each month. 3. There were significant seasonal variations in the urinary excretion of calcium and oxalate, each showing a maximum during the summer months and a minimum in the winter. There was no significant seasonal variation in urinary pH, volume, creatinine, phosphate or magnesium. 4. There was a significant increase in the saturation of urine with calcium oxalate and a trend towards higher saturation levels of octo-calcium phosphate in the summer. These changes were dependent only on the seasonal variation in urinary calcium and oxalate and not on urine volume. 5. A retrospective study of the seasonal incidence of stone episodes among these 246 stone-formers showed that the rate of stone passage per month was 50% higher in the summer than in the winter. There was no significant seasonal variation in the incidence of stones removed surgically.

Calcium↗