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-hydroxyvitamin 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.