Many factors can influence population-based Hb determinations and anemia estimates in population surveys, which in most instances are carried out in environments with limited laboratory capabilities.9 Moreover, environmental factors can also affect the reliability of the measurements, such as extreme temperatures or high humidity, geographical inaccessibility of the setting, logistic, and transportation of the samples obtained (e.g., to maintain the cold chain during transportation). The gene discussed is GSTM1; the disease is anemia (phenotype).