International Journal of Hematology and Oncology 2019, Vol 29, Num 1 Page(s): 031-037
Effects of Immune Complexes on Holotranscobalamine Assay of Vitamin B12 Deficiency in Myeloproliferative Disorders

Demet CEKDEMIR1, Fatma Behice Serinkan CINEMRE2, Birsen AYDEMIR3, Nilgun DILAVEROGLU2, Yasin Ertug CEKDEMIR4, Mehmet GUNDUZ5, Hakan CINEMRE6

1Sakarya University Faculty of Medicine, Department of Internal Medicine, Division of Hematology, Sakarya, TURKEY
2Sakarya University Faculty of Medicine, Department of Biochemistry, Sakarya, TURKEY
3Sakarya University Faculty of Medicine, Department of Biophysics, Sakarya, TURKEY
4Dokuz Eylul University Faculty of Medicine, Department of Radiology, Izmir, TURKEY
5Ankara Atatürk Training and Research Hospital, Department of Hematology, Ankara, TURKEY
6Sakarya University Faculty of Medicine, Department of Internal Medicine, Sakarya, TURKEY

Keywords: Immune complex, Holotranscobalamine, Vitamin B12, Myeloproliferative disorders
In myeloproliferative disorders (MPDs), vitamin B12 levels are measured falsely elevated with conventional methods due to increased carrier protein synthesis. HoloTranscobalamine (HoloTC) assay is a first-choice method for detecting true vitamin B12 deficiency in MPDs. Our aim was to determine effects of immune complexes on HoloTC assay. This is a cross-section study. Vitamin B12 levels in 61 patients with myeloproliferative disorders were measured by both electrochemical immunoassay and HoloTC assay. The HoloTC cutoff was greater than 35 pmol/L. HoloTC assay for each sample were repeated after polyethylene glycol (PEG) treatment to exclude IgG, IgA and IgM type immune complexes. Also, methylmalonic acid, folate, homocystein, liver, and kidney function tests were obtained. Methylmalonic acid test showed that 42 patients (68.9%) had vitamin B12 deficiency. Vitamin B12 levels by HoloTC assay decreased by 19.2±11.28% in essential thrombocytosis, 40.0±9.39% in chronic myeloid leukemia, 30.9±14.62% in myelofibrosis and 21.2±11.55% in polycythemia vera patients after PEG treatment. There was significant difference between the averages of groups (p< 0.01). Methylmalonic Acid Test was used as the B12 status variable. The comparison of ROC curves of HoloTC before and after PEG showed no statistically significance between area under curves. The optimum cut-off points for both HoloTC before and after PEG were 40.6 pmol/L and 32.1 pmol/L, respectively. Immune complexes may have some effect on HoloTC assay which has been recently reported to have a superior diagnostic accuracy for vitamin B12 deficiency in patients with MPDs. Although exclusion of immune complexes did not improve its diagnostic performances, effects of exclusion were significantly different between subgroups of MPDs.