Electrical impedance measurement as an endpoint detection method for routine coagulation tests.

A whole-blood platelet aggregometer is adapted to measure electrical impedance changes in plasma during prothrombin time (PT) estimations. The impedance curve shows an acceleration phase, which is comparable to the absorbance curve acceleration phase associated with the onset of coagulation. The amplitude of the impedance change correlates with the fibrinogen concentration of the plasma. Statistical analysis of PT derived by absorbance and impedance changes shows a significant difference between the two methods but a good correlation. The method is reproducible but laborious and requires attention to technique. Further investigation of the method utilising a more sensitive instrument and redesigned electrodes is indicated. It may also be possible to modify reagent systems to optimise impedance changes.