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1990 Part XII: Hemostasis and Thrombosis Chapter 116: Classification, Clinical Manifestations, and Evaluation of Disorders of Hemostasis 1991

INHIBITORS TO COAGULATION FACTORS disorder (see Fig. 116–2). Chapter 120 contains a flow diagram of the
If an inhibitor is suspected as a result of a prolonged PT or aPTT per- steps required to diagnose the different qualitative disorders of platelet
formed on a 1:1 mixture of the patient’s plasma and normal plasma, function. Additional platelet function assays and glycoprotein analysis
further studies can help define the nature of the inhibitor and its titer. may be required to establish the diagnosis.
Among inhibitors that do not require incubation (i.e., immediate-type),
perhaps the most common cause is the presence of heparin in the sam- REFERENCES
ple. This cause can be verified by finding a prolonged thrombin time
on a test of the patient’s plasma that is corrected with toluidine blue or 1. Miller CH, Graham JB, Goldin LR, Elston RC: Genetics of classic von Willebrand’s dis-
ease: II. Optimal assignment of the heterozygous genotype (diagnosis) by discriminant
other agents that neutralize heparin. The lupus anticoagulant also does analysis. Blood 54:137, 1979.
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able (Chap. 131). However, with lupus anticoagulant, the PT usually is diagnostic indices in coagulation disorders: I. Evaluation of a self-administered ques-
tionnaire with binary questions. Methods Inf Med 19:194, 1980.
less prolonged than is the aPTT, and aPTT reagents have markedly dif- 3. Eikenboom JC, Rosendaal FR, Briet E: Value of the patient interview: All but consensus
ferent sensitivity to lupus-type anticoagulant depending on the amount among haemostasis experts. Haemostasis 22:221, 1992.
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Immunoglobulin inhibitors to specific coagulation factors may 5. Dinehart SM, Henry L: Dietary supplements: Altered coagulation and effects on bruis-
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ited deficiencies of coagulation factors (Chaps. 123 and 124) or sponta- 6. Basila D, Yuan C-S: Effects of dietary supplements on coagulation and platelet function.
Thromb Res 117:49, 2005.
neously in patients without factor deficiencies (Chap. 127). Antibodies 7. Janssen CAH, Scholten PC, Heintz APM: A simple visual assessment technique to
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the patient’s plasma with normal plasma, usually for 2 hours at 37°C, 85:977, 1995.
and then assaying the specific factor. The Bethesda assay originally was 8. Kaplinsky C, Kenet G, Seligsohn U, Rechavi G: Association between hyperflexibility of
designed to quantify factor VIII inhibitors but can be modified to detect the thumb and an unexplained bleeding tendency: Is it a rule of thumb? Br J Haematol
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other inhibitors of coagulation factors (Chap. 123). Some inhibitors 9. Rapaport SI: Preoperative hemostatic evaluation: Which tests, if any? Blood 61:229, 1983.
18
do not directly neutralize clotting activity; instead they reduce factor 10. Sadler JE: Von Willebrand disease type 1: A diagnosis in search of a disease. Blood
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PLATELET FUNCTION DISORDERS 17. McFarlane DE, Stibbe J, Kirby EP, et al: A method for assaying von Willebrand factor
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