SUMMARY Over a period of one year, 24 500 patients underwent a biochemical profile investigation. Seven hundred and thirty-eight (3 %) patients had a plasma calcium concentration of greater than 2-60 mmol/l, and hypercalcaemia was confirmed in 49-8 % of those subjects from whom a second fasting sample was received. Primary hyperparathyroidism and malignant disease were the two commonest causes of hypercalcaemia, occurring with equal frequency. The overall incidence of primary hyperparathyroidism in our population was 1:680. Over 75 % of the patients with primary hyperparathyroidism appeared to have asymptomatic disease. The merits of including a plasma calcium determination in a biochemical profile would seem to depend particularly on the natural history of asymptomatic primary hyperparathyroidism.In 1976 a multichannel analyser was commissioned in our Department and a plasma calcium determination has been included as one of the 14 tests performed on each blood sample submitted for a biochemical profile. In view of several reports describing increased recognition of hypercalcaemia following the introduction ofbiochemical screeningl-4 we conducted over a period of one year a study of patients whose biochemical profile indicated hypercalcaemia. We have looked in particular at the causes of hypercalcaemia and the occurrence of primary hyperparathyroidism. Patients and methodsThe study year extended from 1 October 1978 to 30 September 1979. Samples from patients over the age of 15 y on whom, at the clinician's request, a proffie analysis was performed for the first time during this period were included. Plasma calcium was measured by the method of Gitelman5 modified for use on the Vickers M300 analyser. Our upper limit of normal for plasma calcium is 2 60 mmol/1; this value, representing 2 SD above the mean, was confirmed in samples taken without venous stasis from 50 healthy, ambulant control subjects at the Accepted for publication 27 July 1981 start of the study. When this level was exceeded the referring clinician was invited to submit a fasting sample taken from the patient without venous stasis for a second profile.Plasma PTH was measured by immunoradiometric assay,6 using a predominantly C-terminal antiserum (BW211/41) and a reference preparation of human PTH (75/549) as standard. The sensitivity of the assay was 0-15 ,ug/l and the between-batch coefficients of variation at 0 2 ,ug/l and 1-0 ,ug/l were 13 % and 8 % respectively. The upper limit for PTH in normocalcaemic subjects is 1 ,ug/l. The tubular maximum reabsorptive capacity for phosphate relative to glomerular filtration rate (TmP/GFR) was estimated by the method and nomogram of Walton and Bijvoet.7 The reference range for TmP/GFR was defined in 30 normal subjects as 0 75 to 1-30 mmol/l. The progress of patients with fasting hypercalcaemia was assessed, mostly by inspection of the clinical notes, at least six months after the date of their inclusion in the study. ResultsBiochemical profiles were performed on samples from 24 500 patients. Of these 75% ...

SUMMARY. The performance and clinical utility of a 'C-terminal' parathyroid hormone (PTH) radioimmunoassay (Dac-Cel, Wellcome Diagnostics) is described. Parathyroid hormone, as measured by the Dac-Cel method, is stable in whole blood samples for at least 24 h. 84% of patients with hypercalcaemia due to primary hyperparathyroidism have values above the upper limit seen in normocalcaemic subjects (0,5 ug/L), with detectable serum PTH demonstrable in the remaining 16%. In patients with hypocalcaemia due to hypoparathyroidism serum PTH was undetectable in 73% and 'inappropriately' low in the remainder. In 50% of patients with malignancy-associated hypercalcaemia serum PTH was undetectable, but was above 0·5 ug/L in 13%. Increased PTH concentrations were invariably found in patients with renal failure.The Dac-Cel method is a reliable and robust technique for measurement of PTH and in conjunction with determination of calcium facilitates the diagnosis of primary parathyroid disorders. Caution is required in the interpretation of PTH measurements in patients with renal failure; the significance of detectable PTH in some patients with malignancy-associated hypercalcaemia is not clear.Determination of serum immunoassayable parathyroid hormone (PTH) concentrations forms an important part of the investigation of disorders of calcium metabolism. However, measurement of circulating PTH by radioimmunoassay (RIA) has been bedevilled by the heterogenous nature of circulating PTH and its peripheral metabolism. In recent years, improved understanding of the physiology of PTH secretion and its metabolism, together with the use of well-characterised antisera, has facilitated interpretation of results of PTH in serum. In this report we have evaluated the use of a recently available commercial 'C-terminal' PTH assay (Dac-Cel, Wellcome Diagnostics, Temple Hill, Dartford DA1 5AH, UK) in the investigation of patients with disorders of calcium metabolism. MethodsDac-Cel PTH RIA kits were supplied by

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