Background. Requests of Vitamin B12 test increased with the widespread use of autoanalysers. Although the cause of requests was deficiency suspicions, an important ratio of high levels of Vitamin B12 were reported to physicians by laboratory. Ratios of values of high Vitamin B12 among test request in adults are reported as 14- 20% in present three monocentre studies and one multicentre study. There is no report on children with high vitamin B12 for both ratio in lab requests or clinical follow up.

Methods. We evaluated the records of 40 children (23 male /17 female) with high B12 values ( > 1000 pg/ ml) retrospectively. Children were otherwise healthy children and were seen at outpatient pediatric clinics. Additionally, vitamin B12 values of 13 acute lymphoblastic leukemia patients at diagnosis time were retrieved to enlighten possible role of lymphocytes.

Result. Children did not have any malign or chronic diseases causing the high Vitamin B12 values. Holotranscobalamin levels were normal or slightly above. Two patients did develop leukemia later. Our follow up showed that high vitamin B12 values slightly decreased at 3 months and then remained unchanged later. The high numbers of T and B cells are not the source of vitamin B12 elevation.

Conclusions. Our study suggests that high-vitamin B12 values are usually benign in children but some patients may develop leukemia later. We suggest that patients should be followed up for some time after testing for severe hematological diseases.

Keywords: children, cobalamin, holotranscobalamin, pediatric, vitamin B12