Room temperature radioassay for B12 with oyster toadfish (Opsanus tau) serum as binder

We describe a vitamin B12 radioassay with oyster toadfish (Opsanus tau) serum in which endogenous serum B12 is released from its protein complexes at room temperature with NaOH at pH 13.6. The radioassay is reproducible (CV 4.9% within assay, 8.4% between assays) and sensitive (10 ng/L) and requires minimum manipulations. Assay accuracy is unaffected by serum protein.