A facile colorimetric protamine titration method.

Abstract

On the basis of the reversible, competitive binding of protamine and azure A dye to heparin, a facile, colorimetric protamine titration method was developed. The method uses azure A dye as the titration indicator and has thus replaced the time-consuming clotting assay in the traditional protamine titration method with a rapid colorimetric assay. It offers the same accuracy in estimating the titration end point as the traditional titration method but allows the processing time to be significantly shortened. With the use of a premade diagnostic kit containing a fixed amount of azure A dye and various amounts of protamine, the titration end point can be determined in less than 5 minutes. This new colorimetric protamine titration method should provide clinicians with an easy and reliable means to accurately estimate the protamine dose required for heparin neutralization. It should also assist medical laboratories in preparing plasma samples that are free of heparin interference for routine coagulation tests. In a reverse manner, the colorimetric assay can also be used with a heparin titration procedure to quickly assess the heparin dose required for protamine reversal. For patients who have received overdoses of protamine, the availability of a facile heparin titration method may offer the prospect of exercising a heparin "back titration."