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Richard B. Gilbert, PhD; Elisabeth A. Mailhot, MD
Santa Clara Medical Center San Jose, Calif

JAMA. 1981;246(7):734-735.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

To the Editor.—

Both the title and the conclusions of the recent article by Cohen and Donaldson (1980;244:1942) present a misconception. They (incorrectly) stated that commercial radioassay kits for cobalamin (vitamin B₁₂) are chemically nonspecific and measure inactive cobalamin analogs. This statement was valid in 1978, the time of the initial investigation, but not currently. In this article, the lack of qualifying statements or date-limiting statements implies that the problem of 1978 still exists.

Manufacturers were actually quick to attempt to correct this deficiency in their products, either by cobinamide blocking of "R" proteins or by purification of intrinsic factor by affinity chromatography. As stated in one manufacturer's package insert (⁵⁷Co Vitamin B₁₂ Assay Kit With Purified B₁₂ Binder, package insert, Diagnostic Products Corp, Los Angeles, July 1980), these changes occurred as early as January 1979. The cobinamide-blocked kit used in the follow-up work reported may . . . [Full Text PDF of this Article]

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