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August 26, 1974

Anticoagulant Therapy

Author Affiliations

Valley Memorial Hospital Livermore, Calif

JAMA. 1974;229(9):1167. doi:10.1001/jama.1974.03230470019008

To the Editor.—  In the excellent article entitled "Anticoagulant Therapy—1974" (228:757, 1974), Dr. Wessler states that in the laboratory control of heparin therapy, it is critical that if an activated partial thromboplastin time (aPTT) is used, it must be standardized against the whole blood clotting time (WBCT). It might be inferred from this statement that it is possible to perform the two tests on a group of heparinized patients, and to determine a correlation coefficient high enough to substitute one test for another. This is probably not possible. Colman1 did an excellent study attempting to do this very thing, and achieved a very weak coefficient of correlation of r =.62.Patients heavily heparinized by one standard were lightly heparinized by the other. By contrast, with two chemical tests purporting to measure the same variable, an r value above .95 would be expected before they were considered roughly interchangeable.The problem