Timing of screening for osteomalacia in the acutely ill elderly.

Hypocalcaemia and hypophosphataemia either on admission or before discharge from hospital are poor discriminators for the presence of subclinical osteomalacia in the elderly. Reliance has to be placed on the measurement of alkaline phosphatase even though false positive tests are common. Use of paired admission and predischarge data reduces the false positive rate by approximately 50% thereby reducing the requirement for histological confirmation of the diagnosis of osteomalacia. Since the prevalence of osteomalacia is low in this type of hospital population, any measure which reduces the requirement for bone biopsy is of considerable practical value.