Activated protein C resistance

To the Editor.-In their article, Montes et al1 reported that the cost per test for materials to perform functional screening for activated protein C resistance (APC-R) was less than 20% of the cost for materials to perform "confirmatory" molecular biologic test. The costs cited by these authors are most likely due to the high cost of restriction enzymes. In pricing kits for APC-R, the cost for these reagents alone is about $20 per test. We have instituted a sequence-specific primer polymerase chain reaction assay based on the procedure of Kirschbaum and Foster.2 Using this method, as opposed to restriction fragment length polymorphism, our costs in materials is only about $7 per test. Our sequence-specific primer polymerase chain reaction test can easily distinguish homozygotes from heterozygotes and has built-in quality control in the form of amplification of the gene for growth hormone.

As Montes et al point out, the vast majority of cases of APC- R are attributable to the factor V Leiden (FVL) mutation (R506Q). In most instances, physicians want to identify the inheritable cause of hypercoagulability. Confounding factors, such as pregnancy, oral contraceptive use, and lupus anticoagulant,3 can cause false-positive results in the APC-R functional assay. Thus, despite numerous articles favoring screening with APC-R functional tests,4,5 we advocate testing with the molecularbased polymerase chain reaction test. The decision of a laboratory to screen with a functional APC-R assay should not necessarily be based on the cost of testing, since molecular procedures can be made more costeffective.

RICHARD MACK, DO

ERNEST ALBANESE, PhD

HELEN FERNANDES, PhD

Department of Pathology

University Hospital/ UMDNJ

Newark, NJ 07103

1. Montes M, Fox EA, Longtine JA, Dorfman DM. Comparison of functional testing for resistance to activated protein C and molecular biological testing for factor V R506Q in 370 patients. Arch Pathol Lab Med. 1998;122:325-329.

2. Kirschbaum NE, Foster PA. The polymerase chain reaction with sequence specific primers for the detection of the factor V mutation associated with activated protein C resistance. Thromb Hemost. 1995;74:874-878.

3. Wright JG, Cooper P, Malia RG, et al. Activated protein C resistance in homozygous sickle cell disease. Br J Hematol.1997;96:854-856.

4. Wasserman LM, Edson JR, Key NS, Chibbar R, McGlennen RG. Detection of the factor V Leiden mutation. Am / Clin Pathol 1997;108:427-433.

5. Florell SR, Rodgers GM. Utilization of testing for activated protein C resistance in a reference laboratory. Am / Clin Pathol. 1996;106:248-252.

In Reply.-As Mack et al point out, it may be possible to reduce the cost of molecular biological testing for factor V R506Q by the use of a sequencespecific primer-based polymerase chain reaction assay1 instead of a restriction fragment length polymorphism-based assay. However, the labor costs for molecular biologic testing remain a significant factor in both methods. A simple screening test based on partial thromboplastin time, such as we describe in our report,2 is significantly less labor intensive than either molecular biologic test and may be performed on automated coagulation laboratory instrumentation. The partial thromboplastin time-based screening test that we employed was 100% sensitive in our study, effectively ruling out the factor V R506Q mutation in all patients who were negative for activated protein C resistance. Although molecular biological testing can define specific genetic mutations that lead to disease states, simple inexpensive screening tests to rule out these mutations can provide an effective first line of analysis when available.

JANINA A. LONGTINE, MD

DAVID M. DORFMAN, MD PhD

Department of Pathology

Brigham and Women's Hospital

and Harvard Medical School

Boston, MA 02115

1. Kirschbaum NE, Foster PA. The polymerase chain reaction with sequence specific primers for the detection of the factor V mutation associated with activated protein C resistance. Thromb Haemost. 1 995;74:874-878.

2. Montes MA, Fox EA, Longtine JA, Dorfman DM. Comparison of functional testing for resistance to activated protein C and molecular biological testing for factor V R506Q in 370 patients. Arch Pathol Lab Med. 1998;122:325-329.

Copyright College of American Pathologists Dec 1998
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