A microassay for mammalian renal 25-hydroxyvitamin D3-1-hydroxylase applicable to man.

A micro determination of the renal 25-hydroxyvitamin D3-1-hydroxylase activity was developed that uses as little as 1 mg of rat kidney tissue. The method was applied to the remaining portions of needle kidney biopsy specimens taken for diagnostic purposes from children who had asymptomatic proteinuria and/or hematuria (more than 1-year duration) but were otherwise normal in calcium metabolism and renal function. The 25-hydroxyvitamin D3-1-hydroxylase levels of these children were found to be 66 1,25-dihydroxyvitamin D3 per milligram of tissue per 20 min for an 11-year-old male, 117 pg for a 9-year-old male, and 89 pg for a 10-year-old female.