NEUTROPHIL ALKALINE PHOSPHATASE (NAP)

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Specimen: Blood film from capillary blood collection.

Method: 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.

Application: Investigation of neutrophil leucocytosis, erythrocytosis.

Interpretation: Differentiates chronic myeloid leukaemia (low) from reactive leucocytosis (high), eg bacterial infection. May assist in the differentiation of polycythaemia rubra vera (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.

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

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