Unusual case of pernicious anaemia masquerading as thrombotic thrombocytopenic purpura in the setting of multiple normal vitamin B12 deficiency parameters: preventing anchoring and overdiagnosis.

Timely diagnosis of pseudo-TMA was exceptionally challenging due to several overlapping features with TTP including normal B12 and normal MCV. B12 levels may falsely appear normal in pernicious anemia due to IF-Ab interference with chemiluminescent immunoassay. Schistocytes lower the MCV in automated cell counters. Lower reticulocyte index (<2%), presence of immature/large platelets and teardrop cells, elevated MMA and a higher LDH (>2500) are indicative of B12 deficiency.