An earlier study1 suggested a diagnostic procedure for pancreatic insufficiency associated with cystic fibrosis of the pancreas based upon the determination of plasma glycine following gelatin feeding. West, Wilson, and Eyles2 had shown that a much smaller rise in blood amino nitrogen occurs in children with cystic fibrosis than in normal children after a test meal of casein. Christensen and Shwachman1 confirmed the suggestion that gelatin might serve as a more suitable test protein and were able to avoid (1) the technical difficulties involved in the manometric ninhydrin determination of amino nitrogen or (2) the use of unsatisfactory colorimetric amino nitrogen methods by determining the change in plasma glycine concentration by a suitable method.3 The selection of a single amino acid for estimation was based on the fact that gelatin contains somewhat more than 25% of glycine. The method is, however, not suitable for diagnostic purposes
GOULD BS, SHWACHMAN H. Studies in Cystic Fibrosis: Determination of Plasma Proline Following Protein Feeding as a Diagnostic Test for Pancreatic Insufficiency. AMA Am J Dis Child. 1956;91(6):584–587. doi:https://doi.org/10.1001/archpedi.1956.02060020586011
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