The PT and PTT tests evaluate the coagulation pathway by measuring how long it takes blood to clot. The PT test examines the extrinsic pathway, while the PTT test examines the intrinsic pathway. An increased or prolonged PT can indicate liver disease, vitamin K deficiency, a coagulation factor deficiency, disseminated intravascular coagulation, or anticoagulant therapy.

2. COAGULATION PATHWAY

3. • Prothrombin time (PT) and partial thromboplastin time (PTT)
are tests used to evaluate coagulation, or the clotting of blood.
• The PT test, also known as the PT/INR test, looks at
the extrinsic pathway of coagulation.
• The PTT test looks at the intrinsic pathway of coagulation.

4. • The prothrombin time (PT) test measures how long it takes for
a blood clot to form based on a protein produced by the liver
called prothrombin.
• Prothrombin, also known as clotting factor 2, is one of 13
substances known as "clotting factors" that are involved in
coagulation.

5. • PT is a blood test that measures how long it takes blood to
clot.
• It can be used to check for bleeding problems.

6. • Once blood is drawn, a substance called tissue factor is added to
the test tube. Tissue factor, also known as clotting factor 3,
activates the sample in a way that illustrates how blood would
clot if there is bleeding (the extrinsic pathway).
• Once activated, the PT test is measured in seconds. The time is
then compared to the reference range of values.

7. • A number higher than the reference range means your
blood is taking longer than usual to clot. A number
lower than the reference range means that your blood
is clotting faster than normal.

8. • Clotting Too Quickly
High Vitamin K intake
Estrogen-containing drugs
Deep vein thrombosis
Pulmonary embolism
• Clotting Too Slowly
Vitamin K deficiency
Anticoagulant therapy
Liver disease
Hemophilia
Von Willebrand disease
Sickle cell disease

9. • The PT test does not require fasting but foods high in
vitamin K can skew the results, including beef or pork
liver, green tea, dark green vegetables, or soybeans.

10. • The PT test is sometimes referred to as PT/INR test.
The INR refers to the international normalized ratio, a
calculation that help to ensure the test results are
standardized from one lab to the next.

11. • INR values are important because they help to
determine how well a person is responding to
warfarin, one of the most commonly prescribed
anticoagulants used to prevent blood clots.
• For people on warfarin, the reference range of values
for PT/INR is 2 to 3 seconds.

12. • High and low INR values are interpreted as follows:
• Low INR values mean that you may be at risk
of dangerous blood clots.
• High INR values mean that you may be at risk of
dangerous bleeding.

13. METHODS :
• Quick (One stage) method
• Automated method

14. QUICK (ONE STAGE) METHOD :
• Introduced by Dr Armand Quick in 1935.
• It is the time required for clotting of citrated plasma after
addition of calcium and tissue thromboplastin.

15. REAGENTS & REQUIREMENTS :
• Thromboplastin – Cacl2 mixture reagent
• Control plasma
• Test tubes
• Stop watch
• Centrifuge
• Micropipette
• Micropipette tips
• 3.2% sodium citrate anticoagulated blood sample
• Water bath 37deg C

16. PRINCIPLE :
• The calcium in whole blood is bound by sodium citrate thus
preventing coagulation.
• Tissue thromboplastin to which calcium has been added is
mixed with the plasma and the clotting time is noted.

17. SPECIMEN COLLECTION & STORAGE :
• Collected by veinpuncture using vacutainer & mix the sample.
• Centrifuge at 2500-3000 rpm for 15 minutes.

18. REJECTION CRITERIA :
• Haemolysed sample
• Clotted sample
• Inadequate sample

19. QUICK METHOD ( MANUAL)
• Centrifuge the blood sample at 2500-3000 RPM for 15 minutes.
• Separate the plasma from the cells as soon as possible.
• Label two test tubes as Test tube No. 1 & 2.
• Add 0.1ml of patient plasma to each.
• Label another test tube as control.

20. • Add control plasma 0.1ml.
• Incubates at 37deg C for 1 minute.
• Add 0.2ml of prewarmed thromboplastin reagent into the
tube.
• Start the stop watch.
• Mix the tube & shake it in water bath for 5-6 sec.
• Take out the test tube & observe for clot formation against
light.

21. NORMAL RANGE :
• 11-14 Sec.
• Critical value for urgent clinical notification : > 60seconds.

22. Inr – International Normalized Ratio:
• Introduced by WHO in 1983.
• PT results of different labs using different thromboplastin
reagent may lead to different results even when plasma
warfarin concentration is same, so leads to misinterpretation.
• Hence all Thromboplastin reagents distributed are caliberated
against WHO reference preparation.
• The caliberation no is called International sensitivity index.

23. Indications for obtaining PT are:
• Monitoring vitamin K-antagonists (VKA) such as warfarin is the
most common indication for PT.
• Evaluation of unexplained bleeding.
• Diagnosing disseminated intravascular coagulation (DIC).
• Obtaining baseline value before initiating anticoagulation
therapy.
• Assessment of liver synthesis function and to calculate the
model for end-stage liver diseases (MELD) score in liver disease.

24. INCREASED PT :
• DIC
• Liver diseases
• Vitamin K deficiency
• Oral anticoagulant therapy
• FV, FVII, FX deficiency

25. CAUSES FOR A PROLONGED PT INCLUDE:
• Liver disease
Liver disease or liver dysfunction leads to a decreased
production of most coagulation factors. It leads to
prolonged PT and physical manifestations that can
include petechiae and easy bruising.

26. • Vitamin K deficiency
Vitamin K is a necessary component in factors II, VII, IX,
and X. A deficiency in vitamin K will lead to a decrease
in these factors and prolong PT.
Potential causes that can lead to decreased vitamin K
levels include malnutrition, prolonged antibiotic use,
and impairments with fat absorption.

27. • Factor deficiency
Inherited diseases that lead to a decreased production
of factors II, V, IX, and X will lead to a prolonged PT.
• Disseminated Intravascular Coagulation (DIC)
DIC causes a system-wide activation of coagulation,
depleting available coagulation factors leading to an
increase in PT.

28. • Antiphospholipid antibodies
Antiphospholipid antibody syndrome (APS) characteristically
presents with recurrent thromboembolic events and/or
pregnancy loss along with detected antiphospholipid antibodies
(APA).
APA causes an increased conversion of prothrombin to thrombin
in vivo, leading to an overall decrease in prothrombin. Low
prothrombin levels can lead to an increased PT result.