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Partial Thromboplastin Time

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Taking some herbal products or natural remedies.
  • Taking some medicines, such as antihistamines.

What To Think About

  • The partial thromboplastin time (PTT) and activated partial thromboplastin time (APTT) may be normal in people who have inherited bleeding disorders but have only mild symptoms.
  • The APTT is used to check treatment of people who are using heparin or other blood-thinning medicine to prevent blood clots.
  • Sometimes people who use heparin have a higher APTT because of other substances in their blood and not because of blood-thinning medicines. A test called the heparin neutralization assay may be done to see if this is true.
  • Another blood clotting test, called prothrombin time (PT), measures other clotting factors. Partial thromboplastin time and prothrombin time are often done at the same time to check for bleeding problems. To learn more, see the topic Prothrombin Time and INR.
  • An PTT or APTT is done regularly in people who have bleeding or clotting problems. The tests are also done before procedures or surgeries where too much bleeding may be a concern.

Citations

  1. Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Joseph O'Donnell, MD - Hematology, Oncology
Last Revised September 6, 2012
1 | 2 | 3

WebMD Medical Reference from Healthwise

Last Updated: September 06, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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