Placental alkaline phosphatase (PALP) is an ALP isoenzyme produced by placental syncytiotrophoblast cells during pregnancy. It is the dominant ALP isoenzyme in the third trimester and is physiologically elevated throughout pregnancy. In non-pregnant individuals, any detectable PALP is potentially pathological.
PALP is also known as the Regan isoenzyme when found outside of pregnancy, where it is a recognised paraneoplastic marker associated with several cancers including lung, ovarian, and gastrointestinal malignancies. Detection of PALP in a non-pregnant individual warrants investigation for underlying malignancy.
FAQs
Is elevated ALP during pregnancy a problem?
Not usually. Placental ALP causes a physiological elevation of total ALP in late pregnancy, which can be 2-3 times the normal non-pregnant reference range. This is expected and does not indicate liver or bone pathology. PALP isoenzyme analysis confirms the placental source.
What is the Regan isoenzyme?
The Regan isoenzyme is an alternative name for PALP found in the blood of non-pregnant people with certain cancers. It was named after the first patient in whom it was identified. It is a marker of ectopic placental ALP production by tumour cells.
Which cancers produce PALP?
Lung adenocarcinoma, ovarian cancer, and some gastrointestinal cancers can ectopically produce PALP. It is not a cancer-specific marker but its detection in a non-pregnant person warrants thorough investigation.
Is PALP routinely tested?
No. PALP is measured as part of ALP isoenzyme analysis, which is specifically ordered when the source of elevated total ALP needs characterisation. It is not part of standard blood panels.
