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Temporal Changes in the Activated Protein C Resistance Ratio in a Heterozygote for Factor V Leiden Are Abolished by Dilution in Factor V-Deficient Plasma

Hemostasis and Thombosis Research Laboratory, Walt Disney Memorial Cancer Institute at Florida Hospital, Altamonte Springs, U.S.A.

Maria Garcia

Hemostasis and Thombosis Research Laboratory, Walt Disney Memorial Cancer Institute at Florida Hospital, Altamonte Springs, U.S.A.

Elizabeth Helms

Hemostasis and Thombosis Research Laboratory, Walt Disney Memorial Cancer Institute at Florida Hospital, Altamonte Springs, U.S.A.

Deborah A. Francis

Hemostasis and Thombosis Research Laboratory, Walt Disney Memorial Cancer Institute at Florida Hospital, Altamonte Springs, U.S.A.

John L. Francis

Hemostasis and Thombosis Research Laboratory, Walt Disney Memorial Cancer Institute at Florida Hospital, Altamonte Springs, U.S.A.

Activated protein C resistance (APCR) is the single most common cause of hereditary thrombophilia and is caused by a mutation in the factor V molecule (FV Leiden). Screening for this defect has become a standard part of the laboratory evaluation of thrombophilia. However, the original APTT-based screening test does not discriminate completely between normal individuals and heterozygotes for FV Leiden. Diluting the patient's plasma in factor V-deficient plasma greatly improves the predictive ability of this test for the FV Leiden mutation. In this report we show that a heterozygote for FV Leiden (confirmed by DNA analysis) showed marked temporal variation in APCR ratio when tested by the original coagulation-based technique. Specifically, this individual tested normal in five of seven occasions tested (APCR ratio range 1.98-2.53; normal >2.0). Using the modified method, although some temporal variation remained, the diagnosis of APCR would have been made on every occasion (APCR ratio 1.85-2.12; normal >2.3). These findings constitute a further reason to use the modified procedure for APCR screening. Key Words: Thrombosis-Activated protein C resistance— Laboratory evaluation.

Clinical and Applied Thrombosis/Hemostasis, Vol. 3, No. 2, 99-101 (1997)
DOI: 10.1177/107602969700300205


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