To Estimate the Activity of Alkaline
Phosphatase in Serum^26
26.1 Theory
Alkaline phosphatase (ALP) is a membrane-bound enzyme present mainly in the
liver, bone, intestine, and placenta. ALP shows maximum activity at about pH 10.
This enzyme is intracellular and only a small amount is present in plasma. In certain
disease conditions, the breakdown of cell causes release of enzyme to plasma leading
to increased enzyme levels in plasma. The ALP of normal serum in adults is mainly
derived from the liver and bone and small amount from intestinal component.
During childhood the majority of alkaline phosphatase is of skeletal origin. During
pregnancy, ALP is also contributed from the placenta. ALP is activated by magne-
sium ions. The activity in serum is due to isoenzymes from various organs, but the
major contribution occurs from the liver.
26.2 Specimen Requirements
Serum sample is used. Refrigerated sample is stable for 2–3 days if stored at 0– 4 C
and for 1 month at 25 C. EDTA or oxalate anticoagulants cause extensive inhibi-
tion. Half-life of ALP is 7–10 days.
26.3 Principle........................................
Alkaline phosphatase at alkaline pH hydrolyzes phenyl phosphate to phenol. Phenol
condenses with 4-amino-antipyrin. The condensed product is oxidized by alkaline
potassium ferricyanide to give red-colored complex which is measured at 520 nm.
#Springer Nature Singapore Pte Ltd. 2018
V. Kumar, K. D. Gill,Basic Concepts in Clinical Biochemistry: A Practical Guide,
https://doi.org/10.1007/978-981-10-8186-6_26
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