Mnemonic Monday: Partial Thromboplastin Time vs Prothrombin Time

By Haley Masterson

While PTT and PT will both be affected by disorders of the common pathway of coagulation cascade, the PTT is used as a lab test marker for the function of the intrinsic branch of the coagulation cascade, and the PT for the extrinsic.

Confused yet? Don’t be. Try using this heartbreaking visual mnemonic:

PTT (sometimes also called Activated Partial Thromboplastin Time) measures the intrinsic pathway, because two Ts in the picture above are in a relationship. This test measures all of the coagulation factors except for Factor VII and Thrombin (Factor XIII), and when prolonged can be especially notable as indicating hemophilia or (sometimes) von Willebrand’s Disease.

The PT, on the other hand, measures the extrinsic pathway, because the two Ts are no longer together. They are exes. (Poor “P” is merely a bystander to this romantic tragedy). The PT is used to test Factor 7 (the extrinsic pathway factor).

To remember why Factor VII (7) is associated with PT and not PTT, you have two options:

1. The Scientific Reason: The “P” in Partial Thromboplastin Time stands for “Partial”. Why? Because unlike the PT, the PTT actually doesn’t include Tissue Factor – which is critical in activating 7 to 7a. So by definition, the PTT can’t measure the activity of Factor 7 – there’s no TF to activate it. Therefore Factor 7 must be measured by the PT test.

2. The Extension of the Mnemonic: Factor 7 is in the extrinsic pathway because the infamous “7 year itch” is what caused the two Ts to become exes.



1. Kumar, Vinay, and Stanley L. Robbins. Robbins Basic Pathology. 8th ed. Philadelphia, PA: Saunders/Elsevier, 2007.

2. Le, Tao, and Vikas Bhushan. First Aid for the USMLE Step 1 2010. New York: McGraw-Hill Medical, 2010.



17 thoughts on “Mnemonic Monday: Partial Thromboplastin Time vs Prothrombin Time”

  1. I always remember it as “‘P’lay ‘T’able ‘T’ennis inside” (PTT-intrinsic) and “‘P’lay ‘T’ennis outside (PT-extrinsic)

  2. It would have been easier if your premed course is medical technology/laboratory science. Factor 2 is Prothrombin. Thrombin is ACTIVATED factor 2. 🙂

  3. I remember it as PT ie physical training will done on big ground will be outside so PT is extrinsic and remaining APTT is intrinsic

  4. “This test measures all of the coagulation factors except for Factor VII and Thrombin (Factor XIII)…”
    Thrombin is not Factor XIII….it’s Factor IIa….

  5. And the “exes” (PT) declared WAR (PT is used to measure warfarin). This could be added to the story to also remember that PT measures warfarin vs PTT that measure heparin.

  6. I use WEPT 1972 (Factors 10, 9, 7, 2)
    W=Warfarin, E= Extrinsic PT

    I’ve been a physician for over 25 years. For a mnemonic to be useful to you it’s best if you make it up or understand it very well. Medicine is potentially full of thousands of mnemonics but knowing what it means is most helpful. This site helps!

    Some of the clinical mnemonics (orders, H&P, etc) are so good that once memoized and used on the wards often they become second nature.

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