Evaluation of PG-M3 antibody in the diagnosis of acute promyelocytic leukaemia. 
Acute promyelocytic leukaemia (APL) is a distinct subtype of acute myeloid leukaemia (AML) characterized by a reciprocal translocation, t(15;17) and a high incidence of life-threatening coagulopathy.  APL diagnosis is considered a medical emergency.  As reverse transcription-polymerase chain reaction (RT-PCR) for PML-RAR fusion oncoprotein is time consuming, there is a need for a rapid and accurate diagnostic test for APL.  This study evaluates the role of PG-M3 monoclonal antibody using immunofluorescence (IF) in the early diagnosis of APL.  Thirty-six new untreated APL cases diagnosed with RT-PCR for PML-RAR as the gold standard and 38 non-APL controls (28 non-APL AMLs and 10 non-leukaemic samples) were evaluated by routine morphology and cytochemistry, RT-PCR and IF using PG-M3 monoclonal antibody.  Using IF, 34 of 36 (94·4%) APL cases showed a microgranular pattern suggestive of APL and two cases (5·6%) showed a speckled pattern typical of wild-type PML protein (False negative).  By comparison, two of 28 (7·1%) non-APL AMLs showed microgranular pattern (false positive).  Hence, IF as a diagnostic test for APL resulted in a sensitivity of 94·4%, specificity of 92·9% and positive and negative predictive values of 94·4% and 92·9% respectively.  All 10 non-leukaemic samples showed a speckled pattern.  IF using PG-M3 antibodies can be used as a rapid (takes 2 h), 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.