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Plasma concentrations of calcium fractions, proteins, phosphate and magnesium were measured before, during and after cardiopulmonary bypass in 15 patients undergoing cardiac surgery. When calcium chloride was added to a pump priming solution which contained little or no blood, the concentrations of all calcium fractions were significantly greater after bypass than before, with a mean ionized calcium concentration of 1.52 mmol litre-1 plasma water, 30 min after completion of bypass. This iatrogenic hypercalcaemia was increased significantly by the administration of more than 10 mg kg-1 calcium chloride in the first 30 min after bypass. Other plasma constituents showed the dilutional effect of the pump prime during bypass and only the magnesium concentration failed to return towards normal values after operation.

Plasma calcium, phosphorus, alkaline phosphatase, total protein, and albumin were measured during pregnancy in a group of Asian women living in the south of England and in a control group. The Asian women had slightly lower mean plasma calcium concentrations than the control group. Exposure of Asian women to sunshine appeared to be low, and it was inferred that they probably had little endogenous synthesis of cholecalciferol as a result. Both Asian and control subjects ingested similarly low amounts of vitamin D. The Asian women consumed greater amounts of phytate and vegetable fibres than the controls, and it is suggested that these substances may reduce absorption of insoluble lipids (including cholecalciferol) and calcium in a setting where the dietary intake and endogenous synthesis of vitamin D are already borderline for the subject's requirements.

A recently developed gel-filtration technique allows protein-bound calcium fractions to be separated and quantitated; the protein is separated under physiological conditions of pH, temperature, and concentrations of Na, Mg, and Ca to assure that the calcium-proteinate equilibrium is not disturbed. We used this gel-filtration technique to study the protein-bound calcium fractions in 18 patients with hyperparathyroidism, multiple myeloma, diabetes, osteoporosis, or liver cirrhosis. We calculated the amount of calcium bound per gram of protein for each of the three protein peaks and the intrinsic association constant (Ka) for calcium/albumin. Results with the multiple myeloma patients (three IgG, one IgA) indicated that IgG did not bind calcium appreciably, that IgA had about the same affinity as albumin for Ca, and that Ka was slightly low for one patient of the IgG type (79 L/mol) and normal for the other three myeloma patients (106, 90, and 91 L/mol). Results for patients with the other diseases were also essentially normal, except for the osteoporesis patients (two men, one woman), whose Ka values (69, 75, and 73 L/mol) were lower than normal.

Plasma calcium and magnesium fractions were measured in 51 patients with either hepatocellular or biliary disease. The fractions were found to be only minimally deranged. Plasma albumin correlated with total calcium and with the protein bound and ionized fractions. Abnormalities of plasma calcium or magnesium fractions are unlikely to play a role in the pathogenesis of the osteomalacia seen in chronic biliary disease.

Intravenous calcium infusions produced subjective relief of bone pain in 14 patients with primary biliary cirrhosis. The bone pain had developed despite long-term parenteral vitamin D therapy. The pain returned after two to three months, but a subsequent course of infusions again brought relief. Before treatment satisfactory iliac crest bone biopsies were obtained in 11 of the patients and were normal in seven; two patients had biopsies indicating osteomalacia and two osteoporosis. After treatment a repeat biopsy in one of the patients with osteomalacia showed marked reduction in osteoid. The infusion treatment produced no change in plasma calcium concentration, serum phosphate, or serum alkaline phosphatase. Absorption of oral calcium was also unchanged.

A study is reported of the estimation of plasma calcium fractions and the calcium-binding affinity of plasma proteins in a total sample of 59 people, which included 29 normal subjects and 30 patients with either hypercalcaemia or hypocalcaemia. It was demonstrated that when the sample was considered as a whole there was a significant correlation between the total plasma calcium concentration and the ultrafiltrable, ionized, and protein-bound calcium fractions and between the ultrafiltrable and ionized fractions. We have also demonstrated that in patients with either hypercalcaemia or hypocalcaemia, including acidotic uraemics, the calcium-binding affinity of the plasma proteins did not differ significantly from that in normal subjects. A significant correlation was also found between the total plasma calcium concentration and the ultrafiltrable, ionized and protein-bound calcium fractions when the normal subjects and the groups of patients with hypercalcaemia and hypocalcaemia due to chronic renal failure were considered as separate groups. The group of patients with hypercalcaemia included patients both with hyperparathyroidism and with hypercalcaemia due to other causes.

In 12 normal subjects plasma calcium and phosphorus concentrations were estimated during a normal working day. In the individual subjects fluctuations from the fasting values occurred during the period of study, but at no time during that period did the mean values differ significantly from the fasting plasma calcium or phosphorus concentrations. In three of the subjects the study was repeated while fasting during a normal working day. In these subjects the fluctuations in both plasma calcium and phosphorus concentrations were less than during a normal day while taking meals, and there was evidence of a diurnal variation in the plasma phosphorus concentration.

Urine specimens were collected from 26 normal subjects, 10 patients with proven primary hyperparathyroidism, and eight patients with hypercalcaemia due to other causes. After overnight urine concentration, an oral water load was given to induce a diuresis and provide urine specimens with a relatively wide range of creatinine concentration for each subject. In normal subjects the urinary calcium/creatinine ratio was found to be independent of urine concentration. In eight out of 10 patients with primary hyperparathyroidism and in two out of eight patients with hyper-calcaemia due to other causes, the urinary calcium/creatinine ratio was found to be high when the creatinine concentration was low, but usually normal when the creatinine concentration was high. The results suggest that if the urinary calcium/creatinine ratio of random urine specimens is used as a ;screening' procedure to detect hypercalciuria the latter cannot be excluded if the urinary creatinine concentration is more than 40 mg per 100 ml.

A precise and reproducible method is described for the ultramicro fluorimetric determination of calcium in plasma, based upon the formation of a fluorescent complex between calcium and calcein at a strongly alkaline pH. In a group of normal subjects, the mean concentration of plasma calcium was 9.66 mg/100 ml with a normal range of 8.9 to 10.4 mg/100 ml.