Normally a patient with red cell pyruvate kinase deficiency has a low activity for pyruvate kinase in red blood cells. Rarely a patient with red cell pyruvate kinase deficiency does not show this finding.
Patient selection: non-spherocytic, nonimmunologic hemolytic anemia without hemoglobinopathy
Causes of a normal pyruvate kinase activity:
(1) presence of donor cells after a red blood cell transfusion
(2) incomplete removal of leukocytes
(3) persistence of the muscle (M2) isoform in mature red blood cells
(4) non-physiologic substrate concentrations (causing a failure to detect pyruvate kinase with abnormal kinetics)
When there is a hemolytic episode, older cells with lower levels of pyruvate kinase may be removed, thereby leaving younger erythrocytes with higher levels of pyruvate kinase activity and skewing assay results. After a hemolytic episode the presence of both:
(1) normal pyruvate kinase activity and
(2) elevated activity of other age-dependent red cell enzymes
is suggestive of red cell pyruvate kinase deficiency.
Recommended workup:
(1) examine family members for evidence of red cell pyruvate kinase deficiency
(2) perform sequence analysis for gene mutations
