Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive 
genetic defect that can cause hemolytic crisis. However, this disease affects 
both males and females. In Turkey, the frequency of this enzyme deficiency was 
reported to vary, from 0.25 to 18%, by the geographical area. Its prevalence in 
the northern Black Sea region of Turkey is unknown. The aims of this study were 
to assess the prevalence of G6PD deficiency in the northern region Turkey in 
children and adults with hyperbilirubinemia and hemolytic anemia. This report 
included a total of 976 G6PD enzyme results that were analyzed between May 2005 
and January 2014. G6PD deficiency was detected in 5.0% of all patients. G6PD 
deficiency was significantly less frequent in females (1.9%, 6/323) than in 
males (6.6%, 43/653). G6PD deficiency was detected in 3.7% of infants with 
hyperbilirubinemia, 9.2% of children, and 4.5% of adults with hemolytic anemia. 
In both the newborn group and the group of children, G6PD deficiency was 
significantly more frequent in males. In the combined group of children (groups 
I and II), the proportion of males was 74% and 67% in all groups (P = .0008). In 
conclusion, in northern region of Turkey, G6PD deficiency is an important cause 
of neonatal hyperbilirubinemia and hemolytic crisis in children and adults. This 
study suggests that most pediatricians thought that G6PD deficiency is 
exclusively a male disease. For this reason, some female patients may have been 
undiagnosed.