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Shepard Shapiro, M.D.; Murray Weiner, M.D.
JAMA. 1948;136(6):418. doi:10.1001/jama.1948.02890230058021.
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To the Editor:—  The opinion grows that the results of estimation of prothrombin time should be reported in terms of per cent or of per cent of normal. Recently, a plea has been made that the practice be made universal (Allen, E. V.: The Journal, page 323, May 24, 1947). The main reason for the suggestion has been stated by Barker, Hines, Kvale and Allen: "If clinicians become accustomed to discussing concentrations of prothrombin in terms of percentage rather than time, it is possible to compare the results of the tests performed in many institutions or by individual physicians in different institutions" (Am. J. Med.3:636 [Nov.] 1947). Percentage figures in most published reports are based on the construction of a curve of average prothrombin times of serial dilutions of normal plasmas plotted against the dilutions of these plasmas expressed in the percentage of whole plasma. Not infrequently, there


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