title: Clinical significance of serum vitamin B12 measured by radioassay using pure intrinsic factor.
abstract: Serum vitamin B12 (B12) levels of 53 patients (15 with pernicious anemia) and 42 healthy volunteers were determined using crude intrinsic factor (IF), pure IF, and a mixture of crude IF + R-protein blocking agent (block IF). The radioassay using pure IF showed less sample-to-sample variation in nonspecific binding than the radioassay using block IF. The mean B12 levels in 42 healthy subjects were significantly higher with crude IF (499 +/- 23 pg/ml, 1 s.e.m.) than with pure IF (408 +/- 29 pg/ml) or with block IF (407 +/- 22 pg/ml). B12 levels were abnormally low in all 15 patients with pernicious anemia by pure IF (less than 100 pg/ml), in 14 patients by block IF (less than 150 pg/ml), and in only seven patients by crude IF (less than 200 pg/ml). Our data confirm previous reports that B12 deficiency can be diagnosed more reliably by measuring serum B12 levels with etiher pure IF or block IF.
mesh_terms: D000752:Anemia, Pernicious / Q000097:blood; D006801:Humans; D066298:In Vitro Techniques; D007437:Intrinsic Factor / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011863:Radioimmunoassay / Q000379:methods; D014805:Vitamin B 12 / Q000097:blood*; D014806:Vitamin B 12 Deficiency / Q000097:blood*
chemical_list: D007437:Intrinsic Factor; D014805:Vitamin B 12