A 3-HOUR MEASUREMENT TO EVALUATE BONE CALCIUM TURNOVER

It is well established that short-term clearance of an intravenous cal cium load in vivo reflects bone uptake. Using results from isotope-dil ution experiments with Ca-42, a 3-h test has been developed to measure -a quantity, gamma, related to bone accretion. This test is proposed a s a useful, clinically applicable measure of bone status. For early ti mes, t, after a bolus of Ca-42, plasma tracer dilution was well approx imated by t(-gamma), where gamma is related to the fractional rate of loss of tracer, q, from blood into bone ((l/q)(dq/dt) = -gamma/t). Gam ma was evaluated from kinetic measurements on 91 normal female childre n, adolescents, and adult women in the age range 4-50 years. For t les s than or equal to 3 h, all clearance curves were well fit by a power function. Gamma was found to vary from 0.244 +/- 0.031 for adult preme nopausal women (N = 22) to 0.392 +/- 0.056 for prepubertal children (N = 29). Using the Spearman rank order correlation test, gamma was corr elated with bone accretion measured from classic calcium kinetic studi es with a correlation coefficient of 0.721, significant at p < 0.005. In those cases in which accretion and resorption remain tightly linked , gamma also provides information on the state of calcium loss from bo ne. Gamma was evaluated in 14 subjects with bone disease characterised by increased resorption (osteoporosis, Paget's disease) and in 27 sub jects with decreased accretion (osteogenesis imperfecta, types I, III, IV; steroid-treated juvenile dermatomyositis). All subjects with Page t's disease and with osteoporosis showed increased gamma, consistent w ith high bone turnover. The osteoporotic patients furthermore exhibite d gamma increasing monotonically by approximately 1% per year after ag e 55. The osteogenesis imperfecta patients consistently showed either normal or decreased gamma, depending upon the severity of the disease. The steroid-treated dermatomyositis patients had consistently decreas ed gamma, in concordance with previous studies demonstrating decreased accretion in disease states requiring steroid medication.