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There are various methods for determining the clotting time, the most common being the capillary tube method. It is affected by calcium ion levels and many diseases. Normal value of clotting time is 8 to 15 minutes.
There are several other methods, including testing for those on blood thinners, such as heparin or warfarin. Activated partial thromboplastin time (aPTT) is used for heparin studies and the normal range is 20–36 seconds, depending upon which type of activator is used in the study. Prothrombin time (PT) is used for warfarin studies and the normal values differ for men and women. PT time for adult males' normal range is 9.6-11.8 seconds, while adult females' normal range is 9.5-11.3 seconds. Internationalized normalized ratio (INR) is also a warfarin study, with normal ranges of 2-3 for standard warfarin and 3-4.5 for high-dose warfarin. REFERENCES:
Silvestri, L. A. (2014). Saunders comprehensive review for the NCLEX-RN examination (6th ed.). St. Louis, MO: Elsevier.