G6PD and hyperinsulinemic hypoglycemia, familial, 4: The WHO (1989) [25] classifies G6PD deficiency according to the level of G6PD enzyme activity with Class I is associated with chronic non-spherocytic haemolytic anaemia (CNSHA); Class II as severely deficient with less than 10% residual activity; Class III being moderately deficient with 10±60% residual activity; Class IV showing normal activity of 60±150%; and Class V being increased activity.