Refinements in X-ray Technique for the Estimation of Vitamin D. ∗

Abstract

None of the existing techniques commonly employed for the estimation of Vitamin D are entirely beyond criticism. In choosing the most suitable procedure a number of factors must be considered, depending upon whether time and economy or accuracy and reliability are to receive the most consideration. To indicate briefly some of these factors, we have but to point out the principal advantages and limitations of the 3 widely used methods for the assay of antirachitic potency, in all of which inbred stocks of albino rats furnish the experimental animals.

Since all 3 methods may be adapted to either curative or preventive procedures and since the former enjoy by far the greater vogue in this country, the present discussion and experimental work are limited to curative methods. The Steenbock diet No. 2965 was used to produce rickets, and, in general, the recommendations of the Committee of the American Drug Manufacturers Association on Vitamin Assay were followed. 3

The bone-ash technique as worked out principally by Chick, Roscoe and others 1 , 2 is a purely objective procedure, not subject to aberrations of human judgment, even to the extent that they opcur in the other 2 methods. On the other hand, the factor of biological variation exerts its greatest influence in this method, and the statistical significance of the results can be increased only by proportionally lengthening the series of experimental observations in order that the average figures may not be unduly influenced by such factors as variation in animal stature, susceptibility to rickets, etc.