GSTM1 and anemia (phenotype): Mean Hb concentrations were significantly higher in venous than capillary samples for the full sample (mean ± SD: 12.3 ± 1.7 versus 11.4 ± 1.6 g/dL, P < 0.001), and within each category of anemia, using the venous sample to define anemia (Table 4).