Leukocyte alkaline phosphatase,
LAP is a leukocytosis workup determination on a patient's peripheral
blood smear, either as a direct finger-stick smear or from sodium
heparin anticoagulated blood (the enzyme degrades until a smear is made & dries & is said to degrade quicker in EDTA), doing a granule-positive count on
at least 100 polys (neutrophiles)...grading them as 0-4+. It is an on-site proxy test for cytogenetic & molecular markers. Counts
are multiplied times the numerical positivity grade (such as 20 cells were 1+= 20 points)
and the multiplicands summed to give the LAP score.
If done in a pancytopenia or leukopenia case, it may be VERY challenging to obtain an accurate result (If you can find any
2+, 3+, or 4+ cells, it would be highly doubtful that the case could have a low LAP
) in the low range [see 9/07 memo about LAP] .
Myeloma cases tend to have elevations while MGUS cases are in normal range (an MGUS in the normal range is likely actually an MGUS & not an occult myeloma).
People with occult metastatic malignancy tend to have elevated LAP scores.
normal score (? 7-10 to 30 ?): MGUS.
elevated range (150-250 or higher): infectious inflammatory leukemoid reactions, polycythemia vera, myeloma, pregnancy, newborns, stress, oral contraceptives, other
medications & steroids, estrogen, lithium, and growth factors.
decreased range (<7-10): myeloproliferative syndromes (MPS, especially CML), PNH, ITP, and some myelodysplasia cases.
- LMC lab worksheet notes 2007, W. R. Armstrong, M. D.
(file begun & posted in-progress 5 Oct. 2001; latest addition 5 July 2009)