Serum B12: Sensitivity and Specificity
< 200pg/ml. In patients with MCV > 100. For a diagnosis of B12 deficiency specifically.
In other series, sensitivity is not 100% - per PMID 2339684, a series of pernicious anemia patients who were receiving less than the proper maintenance dose had elevated MMA levels in 95% of the case while decreased cobalamin was only present in 69%. In the same study, a series of 400 patients with "clinically significant" B12 deficiency had a 97% sensitivity for low B12 levels.
100% sensitive, 95% specific