[Determination of heat stable alkaline phosphatase]

In this work the method for determination of serum heat-stable alkaline phosphatase (HSAP)--valuable as a placenta function test in pregnancy--is discussed. There are different informations about the optimal conditions for inactivating the nonplacental heat labile isoenzyms, and therefore the opinions on the clinical efficiency of HSAP vary in different studies. Sera of nonpregnant and pregnant females were heated at 40 degrees to 65 degrees C for 5 to 60 minutes. It is demonstrated, that in opposite to suggested opinions in several reports a temperature of 56 degrees C for 30 minutes is notsufficient to inactivate all nonplacental alkaline phosphatase isoenzymes. At 60 degrees C for 20 minutes and at 65 degrees C for 5 minutes in sera of pregnant and nonpregnant female controls we could find concordant results, so that these two conditions of inactivation are regarded as the best. We prefer a temperature of 60 degrees C and inactivate for 20 minutes, since these conditions are to reproduce more easy and allow a beter precision of the results, than 65 degrees C for 5 minutes.