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 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.