Determination of bone turnover by urinary excretion of 99mTc-MDP

Two methods of estimating bone turnover were investigated. The 24 h whole body retention (WBR) of intravenously injected 99mTc methylene disphosphonate (99mTc-MDP), a precise, accurate, and generally accepted method, was compared with a new, simple, measurement involving assessment of the 24 h urinary excretion (UE) of 99mTc-MDP. The WBR and UE were measured in 50 normal subjects, 10 patients with thyrotoxicosis, and 10 patients with chronic renal failure. The precision was 4.8% and 2.7%, respectively, and the two methods were highly significantly correlated (r = 0.99, SEE = 2.9%, p less than 0.001). In addition, urinary 99mTc-MDP excretions at 0 h-4 h (UE4) and 0 h-8 h (UE8) after injection were calculated in 49 subjects. The estimation of WBR from UE4 or UE8 was considerably poorer than from UE (for UE4: r = -0.83, SEE = 8.7%, and for UE8: r = -0.90, SEE = 6.8%) and the precision of UE4 and UE8 was 7.2% and 7.8%, respectively, and greater than those of both UE and WBR. It is concluded that the UE bone turnover measurement may become a simple, radiation dose-saving method to diagnose and monitor the treatment of metabolic bone diseases.