Evaluation of a flow cytometric test for G6PD-deficient erythrocytes

OBJECTIVE

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, an X-linked recessive disorder, is the commonest erythrocytic enzymopathy worldwide. Reliable diagnosis and severity prediction in G6PD-deficient/heterozygous females remain challenging. A recently developed flow cytometric test for G6PD deficiency has shown promise in precisely identifying deficient females. This paper presents our experiences with this test in a subtropical setting and presents a modification in flow cytometric data acquisition strategy.

METHODS

The methaemoglobin reduction + ferryl Hb generation-based flow cytometric G6PD test was compared with the screening methaemoglobin reduction test (MRT) and confirmatory G6PD enzyme activity assay (EAA) in 20 G6PD-deficient males, 22 G6PD-heterozygous/deficient females and 20 controls. Stained cells were also assessed for bright/dim G6PD activity under a fluorescent microscope.

RESULTS

Flow cytometry separated and quantified %bright cells in heterozygous/deficient females, objectively classifying them into 6 normal (>85% bright cells), 14 intermediate (10-85%) and two G6PD-deficient (<10% bright cells). Concordance with MRT was 89% (55/62 cases) and with EAA was 77% (48/62 cases). Fluorometrically predicted violet laser excitation (405-nm) with signal acquisition in the 425-475 nm region was a technical advancement noted for the first time in this paper.

CONCLUSION

Flow cytometry/fluorescence microscopy represent technically straightforward methods for the detection and quantification of G6PD-deficient erythrocytes. Based on our results, we recommend their application as a first-line investigation to screen females who are prescribed an oxidant drug like primaquine or dapsone.

Acute monocytic leukemia presenting as generalized lymphadenopathy and skin rash in a toddler: highlighting the clinicopathologic mimics

Acute myeloid leukemia (AML) is the fifth most common malignancy in children. Extramedullary involvement in acute myeloid leukemia is rare and can be seen in soft tissues, central nervous system, skin and lymphoreticular organs. The clinical presentations can often be non-specific and hence, the diagnosis can be very challenging, especially in cases without a prior hematologic diagnosis. We report a case of pediatric acute monocytic leukemia presenting with generalized lymphadenopathy and cutaneous rash. Fine-needle aspiration was performed from the lymph nodes and a cytologic diagnosis of infiltration by a lymphoreticular malignancy was suggested. Peripheral blood, bone marrow and cerebrospinal fluid involvement were noted subsequently. Flow cytometry on the bone marrow aspirate confirmed a diagnosis of acute monocytic leukemia. The index case besides highlighting an uncommon presentation of acute monocytic leukemia in a toddler, also emphasizes the need to consider acute monocytic leukemia as a cytomorphologic differential in such presentations.