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Kaolin clotting time (KCT) is a sensitive test to detect lupus anticoagulants.[2] There is evidence that suggests it is the most sensitive test for detecting lupus anticoagulants.[3] It can also detect factor VIII inhibitors but is sensitive to unfractionated heparin as well.[4]

Kaolin clotting time
Medical diagnostics
Test ofBlood plasma[1]



KCT was first described by Dr. Margolis in 1958.[5]


KCT is similar to the activated partial thromboplastin time test, except it does not use exogenous phospholipid.[2] Thus, a confirmatory test that uses excess phospholipid is needed to validate the presence of lupus anticoagulants.[2]

Kaolin is the surface activator, and the test also requires small amounts of cell fragments and plasma lipids to provide the phospholipid surface required for coagulation.[2][4] Therefore, the sample quality is important for the validity of the test.[2]



The test combines a test plasma with kaolin, and the time the clot (in seconds) is measured.[5]


If the KCT is less than 60 seconds, this suggests that the normal control plasma is contaminated with platelet fragments; therefore, the test is not valid.[4]

The KCT test/control ratio of greater than or equal to 1.2 indicates an inhibitor is present.[4] If the test/control ratio is between 1.1 and 1.2, the test is equivocal.[4]

See alsoEdit


  1. ^ Gronowski, Ann M. (2004). Handbook of Clinical Laboratory Testing During Pregnancy. Springer Science & Business Media. p. 308. ISBN 9781592597871.
  2. ^ a b c d e Radhakrishnan, Kottayam (2013). Kaolin Clotting Time. Methods in Molecular Biology. 992. pp. 335–339. doi:10.1007/978-1-62703-339-8_25. ISBN 978-1-62703-338-1. PMID 23546725.
  3. ^ Exner, T; Triplett, D. A.; Taberner, D. A.; Howard, M. A.; Harris, E. N. (1990). "Comparison of test methods for the lupus anticoagulant: International survey on lupus anticoagulants-I (ISLA-1)". Thrombosis and Haemostasis. 64 (3): 478–84. PMID 2128977.
  4. ^ a b c d e "Kaolin Clotting Time [KCT]". Retrieved 26 November 2014.
  5. ^ a b Margolis, J (1958). "The kaolin clotting time; a rapid one-stage method for diagnosis of coagulation defects". Journal of Clinical Pathology. 11 (5): 406–9. PMC 479806. PMID 13575555.