Background: The measurement of protein binding is essential for accurate quantitative studies of skeletal kinetics using Tc-methylene diphosphonate (Tc-MDP). In this study, the dependence of Tc-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 Tc-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 Tc-MDP and 3 MBq Cr-EDTA. Free Tc-MDP was measured using ultrafiltration and the percentage of free Tc-MDP analysed for the effect of Ktotal and serum albumin concentration using multivariate regression analysis.
Results: When the percentage of free Tc-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 Tc-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 Tc-MDP measured at the 2, 3 and 4 h time points.