Figure 1
WHO classification of G6PD variants according to the degree of enzyme deficiency and severity of haemolysis
| Class I | Severe enzyme deficiency (<1% residual activity) chronic non-spherocytic haemolysis |
| Class II | Severe enzyme deficiency (1–10% residual activity) intermittent acute haemolysis |
| Class III | Moderate enzyme deficiency (10–60% residual activity) intermittent acute haemolysis |
| Class IV | No enzyme deficiency (60–150% activity) |
| Class V | Increased enzyme activity (>150%) |