Rapid Immunoassay Used to Diagnose Acute Leukemia.

An immunofluorescence (IF) assay, using monoclonal antibodies, has been evaluated for the diagnosis of acute promyelocytic leukemia (APL), which is considered a medical emergency.

APL is a distinct subtype of acute myeloid leukemia (AML) characterized by a reciprocal translocation, and a high incidence of life-threatening coagulopathy. As reverse transcription-polymerase chain reaction (RT-PCR) for the promyelocytic leukemia (PML) - retinoic acid receptor (RAR) alpha fusion oncoprotein is time consuming, there is a need for a rapid and accurate diagnostic test for APL.

A study was carried out at the All India Institute of Medical Sciences, (New Delhi, India), to evaluates the role of the monoclonal antibody, PG-M3, using immunofluorescence (IF) in the early diagnosis of APL. PG-M3 antibodies are specifically directed against a peptide sequence located in the amino-terminal region of the human PML protein. Thirty-six new untreated APL cases diagnosed with RT-PCR for PML-RAR alpha as the gold standard and 38 non-APL controls (28 non-APL AMLs and 10 non-leukemia samples) were evaluated by routine morphology and cytochemistry, RT-PCR, and IF using PG-M3 monoclonal antibody. The median age of APL patients was 35 years (range 9–75 years) and included 19 men and 17 women.

The IF assay, using the PG-M3 antibodies, takes two hours to perform. Of the 36 APL cases, 34 (94.4 %) showed a microgranular pattern of immunofluorescence (IF) and two cases (5.6%) showed speckled pattern indicating possible false negatives. Of 28 non-APL AML controls, 26 (92.9%) showed a speckled pattern and two (7.1%) cases showed microgranular pattern indicating false positives. IF was significantly superior compared with morphology alone for the diagnosis of APL. All 10 non-leukemic controls were correctly identified as negative for APL on both morphology and IF (speckled). There were no cases or controls, which could not be evaluated by IF. The study was published online on August 4, 2010 in the European Journal of Clinical Investigation.

The authors concluded that, PG-M3 antibodies could be used as a rapid, cheap, sensitive, and specific method to identify APL. It can be a useful adjunct for diagnosis of APL especially if facilities for RT-PCR are not available, particularly in resource-limited settings.

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All India Institute of Medical Sciences