The current invention is a method, kit and reagents for detecting cobalamins in a sample. The method involves introducing into the sample a first conjugate of a latex or latex-like solid phase linked to affinity purified intrinsic factor with a first linking group at least three angstroms long. The first conjugate and the bound cobalamins in the sample are then exposed to a second conjugate of a cobalamin linked to a detectable enzyme to produce second conjugate bound to first conjugate and unbound second conjugate. The enzyme activity associated either with the solid phase first conjugate or the unbound second conjugate is then detected. By linking affinity purified intrinsic factor to a latex or latex-like solid phase with a first linking group at least three angstroms long, an enzyme assay can be performed which detects levels of cobalamins in patient samples within or below normal ranges found in such samples.