Neutrophil alkaline phosphatase (NAP)

Last updated: Thursday, 06, April, 2006

This test is not commonly used and is probably obsolete.

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Item Process

Blood film from capillary blood collection or heparinized blood. The test is preferably performed within eight hours of collection.


Semiquantitative cytochemical assessment of alkaline phosphatase in neutrophils.

The NAP score is based on staining intensity with a possible score of 0-400.

Reference Interval

Method dependent. Typically 30-180.


Investigation of neutrophil leucocytosis, erythrocytosis.


Differentiates chronic myeloid leukaemia (low) from reactive leucocytosis (high), eg, bacterial infection.

May assist in the differentiation of polycythaemia vera (PV) (high) from other causes of erythrocytosis (normal).

Diagnosis of paroxysmal nocturnal haemoglobinuria (very low); normal to high in other haemolytic and/or hypoplastic anaemias.

The NAP is moderately elevated in pregnancy, with oestrogen therapy (eg, oral contraception) and corticosteroid therapy.


Bain BJ. Blood Cells - a Practical Guide. Blackwell Science 1995.