Intact erythrocytes. A: Negro male with marked G6PD deficiency. All erythrocytes are devoid of formazan granules. B: Caucasian male with spectrophotometrically normal G6PD activity. All erythrocytes contain formazan granules. C: Chinese female with intermediate expression of G6PD deficiency. Mosaicism is easily seen in that many cells have abundant formazan granules, and many are devoid of granules (×1,000). (From: Fairbanks VF. Blood 1968;31(5):589-603, with permission from the American Society of Hematology.⁵⁴)