Objective: Hypotonia, lethargy, eczema, alopecia, conjunctivitis, ataxia, hearing loss, optic atrophy, cognitive retardation, and seizures can be seen in biotinidase deficiency. This study aimed to compare the hemogram values of infants with biotinidase deficiency and healthy infants.

Material and Method: Hemogram data of 35 cases who were found to have biotinidase deficiency with the neonatal screening program and 41 healthy infants were recorded retrospectively.

Results: While 51.4% of 35 cases in the patient group were male and the mean age at presentation was 19,02±5,485 days, 51.2% of 41 cases in the control group were male and the mean age at presentation was 15,41±7,269 days. While a statistically significant elevation was found in the total leukocytes, lymphocytes, monocytes, thrombocyte, MPV, PCT and MCHC values in the patient group compared to the control group; a statistically significant decrease was detected in basophil, MCV and RDW values.

Conclusion: In the patients with biotinidase deficiency, higher levels of white blood cells, lymphocytes and platelets were detected compared to the control group. These higher rates are thought to be a part of the mechanism leading to immune dysfunction and hair and skin abnormalities in biotini-dase deficiency.