Calibration drift in the automated determination of calcium and magnesium by atomic absorption.

Calibration drift was studied in the automated on-line determination of calcium and magnesium by atomic absorption over periods of up to four hours. Automatic correlation for drift improved the precision of results.

A calibration procedure for the determination of alkaline phosphatase with the autoanalyzer.

We describe a kinetic procedure using the LKB reaction rate analyser for the calibration of an AutoAnalyzer alkaline phosphatase method. Measurements were made at zero incubation time with a special lid for the thermostated tunnel of the LKB reaction rate analyzer using assay conditions appropriate to the AutoAnalyzer method. The molar absorptivity of p-nitrophenol was estimated on the LKB reaction rate analyser used for assay of the enzyme standards. Other variables affecting the accuracy of the measurement were also determined.

A comprehensive laboratory computer system working round the clock.

The special features of a laboratory computer system operated by laboratory staff around the clock are presented. The system provides registration of work, production of worksheets, on-line data acquisition and reporting results. The reasons for the special design features are discussed.

Hypomagnesaemia in diabetes.

The plasma magnesium (Mg) concentrations of 582 unselected diabetic outpatients and 140 control subjects were measured by atomic absorption spectrophotometry. Mean plasma Mg (+/-S.D.) was significantly lower in the diabetic patients (0.737 +/- 0.071 mmol/l) than in the control subjects (0.810 +/- 0.057 mmol/l), and 146 (25%) diabetics had values below those of all control subjects except one. Plasma Mg correlated best with clinic blood glucose concentration (r = -0.32, p less than 0.001) and other significant associations were observed with glycosuria, age, sex, insulin therapy and biguanide therapy. Although its significance is unclear, hypomagnesaemia could conceivably predispose to ischaemic heart disease in diabetes.

Comparison of three parathyroid hormone assays.

The efficiency of three parathyroid hormone (PTH) assays in the diagnosis of primary hyperparathyroidism has been investigated. Two assays used commercial reagents and measured the intact hormone and middle region of parathyroid hormone and the third assay employed the antiserum AS 211/32. Although the intact and mid-molecule assays showed a greater increase in PTH above normal than the laboratory PTH assay, patients with proven primary hyperparathyroidism were not distinguished from healthy subjects in every case. The intact and in house assays gave elevated values in seven out of nine patients with proven hyperparathyroidism and the mid-molecule assay in eight out of nine assays. The intact PTH and in-house assays were more successful than the mid-molecule method in separating patients with primary hyperparathyroidism from those with hypercalcaemia due to malignancy.

Stability of parathyroid hormone-related protein and parathyroid hormone at room temperature.

The stability of plasma parathyroid hormone-related protein (PTHrP) as measured by the Nichols Institute assay at room temperature was assessed over a period of 72 h in blood samples collected in protease inhibitor tubes and EDTA tubes at 0, 6, 24, 48 and 72 h from 10 patients with hypercalcaemia of malignancy. Mean plasma PTHrP concentrations in blood samples collected in protease inhibitor tubes remained stable for up to 48 h but had decreased by 10% at 72 h. The mean EDTA plasma PTHrP at zero time was 67% of the protease inhibitor tube value and this had fallen to 39% at 72 h. The stability of parathyroid hormone (PTH) in separated blood samples was also assessed by collection into heparin and plain tubes as well as EDTA and protease inhibitor tubes. Serum PTH concentrations progressively declined throughout the 72 h study period although the zero time values were significantly higher than corresponding plasma PTH concentrations. Plasma PTH concentrations appeared to be stable when blood was collected in heparin, EDTA and protease inhibitor tubes during the 72 h period, except in one subject with markedly elevated plasma amylase activity.

A comparison of five curve-fitting procedures in radioimmunoassay.

Data obtained from routine analytical radioimmunoassays were processed using five curve-fitting procedures, viz. 'Amersham', single binding site, four parameter logistic, a linear logit-log and a polynomial logit-log. The polynomial logit-log procedure gave the best fit, but this was probably due to the inherent flexibility of this curve-fitting process since the analytical precision achieved with it was not better than what was obtained with most of the other procedures. A limited study failed to show that statistical weighting of data before curve fitting had any practical advantage.

Use of an enzyme standard in the measurement of enzymes in a Clinicon reaction rate analyser.

Measurement of enzyme activity in a Clinicon reaction rate analyser was carried out in two ways: one method was based on absolute calibration and the other used an enzyme standard which involved adjustment of results according to the value for the standard obtained in each batch. Batch calibration significantly improved long-term precision and reduced differences between results obtained in different instruments.

Plasma endothelin in coronary venous blood from patients with either stable or unstable angina.

STUDY OBJECTIVE: To test the hypothesis that the active coronary endothelial lesions in unstable angina raise the endothelin concentration in coronary venous blood. DESIGN: Systemic and coronary venous blood samples were obtained from unselected patients with the clinical syndromes of either stable or unstable angina at the time of cardiac catheterisation and coronary arteriography. Control venous blood samples were obtained from healthy laboratory workers and from patients with chronic renal failure treated by intermittent haemodialysis. PATIENTS: Twelve patients with angina: seven with stable symptoms and five with unstable angina. RESULTS: The mean coronary venous endothelin concentration in unstable angina was 2.32 ng/l (range 1.7-3.2 ng/l). In stable angina it was 2.77 ng/l (range 2.1-4.4 ng/l). These values were not significantly different from one another nor from the values obtained in systemic venous blood from either group or from the healthy controls. Circulating endothelin concentrations were much higher in venous blood from the patients treated by haemodialysis. CONCLUSIONS: These data do not support the hypothesis that raised endothelin concentrations in coronary blood in patients with unstable angina may modulate variations in coronary arterial tone thereby contributing to the clinical syndrome of chest pain and electrocardiographic changes at rest. The raised endothelin concentrations seen in systemic venous blood after myocardial infarction may be part of the systemic response to myocardial infarction.

Diurnal profiles of plasma magnesium and blood glucose in diabetes.

In order to study the relation between plasma magnesium and blood glucose concentrations in diabetes, diurnal profiles were obtained in nine diabetic patients and five healthy subjects. A significant inverse relationship between the two variables was found in seven of the nine diabetic patients and in one healthy subject. This could not be attributed solely to changes in plasma albumin, and its mechanism is unclear. Plasma magnesium levels in diabetes are closely dependent on blood glucose concentration.

Relationship between vitamin A and bone disease in chronic renal failure.

A study has been made of possible interrelationships between circulating vitamin A concentration and indicators of altered calcium homeostasis in 31 patients with stable chronic renal failure. Plasma retinol concentrations were high, possibly as a result of increased retinol-binding-protein concentrations secondary to renal failure. There was no correlation between retinol concentration and any other measurement, including vitamin A intake. However, there were significant correlations between plasma parathyroid hormone and calcium, phosphate, alkaline phosphatase, urea, and creatinine concentrations; and those patients with radiological sub-periosteal erosions tended to have the highest concentrations of circulating parathyroid hormone. Our data give no support to the contention that vitamin A status has any bearing on the progression and severity of the hyperparathyroid bone disease of renal failure.

Serum insulin-like growth factor-1 is not a useful marker of prostate cancer.

OBJECTIVE: To determine whether the use of serum insulin-like growth factor 1 (IGF-1) levels is more efficient than serum prostate specific antigen (PSA) levels in predicting prostate cancer in patients undergoing prostatic biopsy. PATIENTS AND METHODS: The study included 94 consecutive patients who required transrectal ultrasonography (TRUS)-guided biopsies of their prostate and who had blood samples taken before their biopsies. These samples were then analysed for IGF-1 and PSA concentrations. Six prostatic biopsies were taken from each patient; they were assessed and a diagnosis made of prostate cancer or no malignancy. RESULTS: Thirty-seven patients were found to have prostate cancer and 57 had no evidence of malignancy. There was no statistical difference in serum IGF-1 levels between these groups. The PSA level and age of the patients differed significantly between the groups (both P<0.001). There was no correlation between IGF-1 and PSA levels, and even when the age difference in the groups was considered, there was still no significant relationship between IGF-1 levels and the incidence of prostate cancer. In patients with a PSA level of 4-20 microg/L there was no statistically significant difference in IGF-1 levels between the groups. CONCLUSION: Serum IGF-1 as a tumour marker does not help to predict patients with prostate cancer. PSA level and even age were better predictors of the presence of prostate cancer than were serum IGF-1 levels.

Detection of osteomalacia in British Asians: a comparison of clinical score with biochemical measurements.

1. In a prospective study of 160 Asian outpatients, plasma calcium, phosphate, alkaline phosphatase, 25-hydroxyvitamin D and parathyroid hormone were compared with a clinical score to determine which measurements singly or in combination were most useful in the detection of osteomalacia. 2. Bone biopsies were performed in 45 of 48 patients considered to be at risk of osteomalacia. Of the 39 quantifiable bone biopsies, nine showed unequivocal osteomalacia, 13 were judged to be borderline and 17 biopsies were normal. 3. The clinical score was highly sensitive, identifying eight of nine patients with osteomalacia, but not specific, six of 17 normal patients having an abnormal score. 4. Plasma parathyroid hormone was the best single biochemical test for identifying osteomalacia. By using a discriminant function based on parathyroid hormone and alkaline phosphatase, it was possible to classify 96% cases correctly; a discriminant function utilizing calcium, phosphate and alkaline phosphatase was successful in 85% of cases. It was not possible to discriminate between histological groups on the basis of plasma 25-hydroxy-vitamin D values. 5. We confirm that the clinical score is a useful and inexpensive screening test for osteomalacia in British Asians. In those patients with an abnormal score we suggest that parathyroid hormone and alkaline phosphatase are measured. Where both parathyroid hormone and alkaline phosphatase are high, in the absence of hypercalcaemia, histological osteomalacia is extremely likely.