A study to determine the dependence of 99mTc-MDP protein binding on plasma clearance and serum albumin concentration

Background: The measurement of protein binding is essential for accurate quantitative studies of skeletal kinetics using 99mTc-methylene diphosphonate (99mTc-MDP). In this study, the dependence of 99mTc-MDP protein binding on total plasma clearance (Ktotal) and serum albumin concentration was investigated using data from two groups of patients.

Method: The first group (study 1) consisted of 71 patients referred for a 99mTc-MDP bone scan examination. The second group (study 2) consisted of 100 subjects referred for a determination of glomerular filtration rate (GFR) and injected with 3 MBq 99mTc-MDP and 3 MBq 51Cr-EDTA. Free 99mTc-MDP was measured using ultrafiltration and the percentage of free 99mTc-MDP analysed for the effect of Ktotal and serum albumin concentration using multivariate regression analysis.

Results: When the percentage of free 99mTc-MDP was analysed for the effect of Ktotal and serum albumin, highly significant relationships were found at the 2, 3 and 4 h time points. Subjects with higher values of Ktotal or serum albumin concentration had a lower percentage of free 99mTc-MDP and the magnitude of the regression coefficients increased with time.

Conclusion: Multivariate regression analysis confirmed that Ktotal and serum albumin were highly significant factors in determining the percentage of free 99mTc-MDP measured at the 2, 3 and 4 h time points.