Which isoenzyme of ALP is most heat-stable?

The most heat-stable isoenzyme of alkaline phosphatase (ALP) is indeed the placental isoenzyme. The heat stability of the different ALP isoenzymes varies significantly, and the placental isoenzyme has a greater resistance to heat inactivation compared to the others.

This heat stability is particularly important in clinical laboratory settings where sample processing and transport may involve exposure to elevated temperatures. When performing tests that involve the measurement of ALP levels, knowing that the placental isoenzyme retains its activity under such conditions can aid in obtaining accurate results, especially in cases where isoenzyme identification and differentiation are necessary.

Other isoenzymes, such as those from bone or liver, are more susceptible to heat and thus may lose activity when exposed to higher temperatures. The intestinal isoenzyme, while also important in various physiological functions, does not exhibit the same level of thermal stability as the placental isoenzyme. This distinction is crucial for clinicians when interpreting ALP results and understanding the underlying physiological conditions they may indicate.