1: Acta Haematol 2000;104(1):22-4 Oral contraceptives can cause falsely low vitamin B(12) levels. Gardyn J, Mittelman M, Zlotnik J, Sela BA, Cohen AM. Hematology Unit, Golda-Hasharon Campus, Rabin Medical Center, Petah Tikva, Israel. Serum vitamin B(12) radioimmunoassays may give falsely low results in patients with folate deficiency, multiple myeloma, megadose of vitamin C and following radioisotope organ scan. We evaluated 10 consecutive healthy women on oral contraceptives (OC) who had falsely low vitamin B(12) levels, as reflected by normal urine methylmalonic acid and plasma homocysteine. After 1-month cessation of OCs, vitamin B(12) returned to the normal range in all women. Transcobalamin I (TCI) blood level was decreased in 60% of patients. OCs may cause temporary low vitamin B(12) blood levels of no clinical significance that can be associated with low TCI levels Copyright 2000 S. Karger AG, Basel PMID: 11111117 [PubMed - indexed for MEDLINE]