Partial Thromboplastin Time (PTT) Test

What is Prothrombin Time Test?

PTT (Partial Thromboplastin Time) Test measures the time it takes blood to clot. This simple blood test measures how well certain proteins, called clotting factors, are working. These proteins go through a series of reactions to stop bleeding when there is injury.

This test measures the intrinsic and common pathway of the blood-clotting process involving factors I, II, V, VII, IX, X, XI and XII. The test is sometimes referred to as the Activated Partial Thromboplastin Time (aPTT) Test because an activating substance is added to the sample during laboratory analysis.

Your healthcare provider may order a PTT test to help evaluate unexplained bleeding or bruising. It detects some inherited and acquired bleeding or clotting disorders. Also, it monitors treatment with unfractionated heparin (blood-thinning medicine).

The PTT test is often done in conjunction with the Prothrombin Time (PT) Test and other coagulation tests to obtain a more complete assessment and examine different parts of the clotting process. The healthcare provider can see a more complete picture of how well the blood is clotting by comparing both results.

What Symptoms Prompt This Test?

A healthcare provider may recommend a PTT Test when a person has signs of abnormal bleeding, a history of blood clots or a condition that may affect clotting.

Signs of a Possible Bleeding Problem

• Bruising easily without a clear reason 
• Frequent or heavy nosebleeds 
• Bleeding for longer than expected after a small cut 
• Heavy or prolonged menstrual bleeding 
• Blood in urine or stool 
• Bleeding after dental treatment, injury or surgery 
• Painful or swollen joints caused by internal bleeding 
• A personal or family history of a bleeding disorder

Other Reasons for Testing

The test may also be requested when a person:

• Is receiving unfractionated heparin 
• Has liver disease 
• Has experienced an unexplained blood clot 
• Has a history of recurrent pregnancy loss 
• Is being evaluated for antiphospholipid syndrome 
• Is preparing for surgery and has a history suggesting unusual bleeding 

PTT testing is not routinely needed before every operation. The decision usually depends on the person’s medical history, symptoms and risk of bleeding.

How is the Test Performed?

Preparation

• Usually fasting is not necessary.
• Inform your health care provider about all medications and supplements you are taking, including anticoagulants such as heparin, as these medications can affect the test result.
• Follow specific instructions from your health care provider or laboratory, if any.
• Do not stop taking prescribed blood-thinning medication unless your health care provider tells you to.

Sample Collection

The phlebotomist cleans the skin (site of sample collection) with an antiseptic solution. A sterile needle is used to draw blood from a vein. When a sufficient amount of blood is collected in the sample tube, the needle is withdrawn. Slight pressure is applied to the puncture site. This generally takes a few minutes and may cause slight discomfort or mild bruising.

Blood is drawn into a special tube which contains sodium citrate. It prevents the blood from clotting before analysis/coagulation testing.

Precaution

The sample tube must contain the correct amount of blood because an incorrect blood-to-citrate ratio can affect the result.

Lab Analysis

In the laboratory, plasma is separated from the blood cells. An activator is then added to start clot formation. The laboratory records the time taken for a clot to form and reports it in seconds.

A prolonged result may sometimes be caused by sample-related issues rather than a health condition. These may include an underfilled collection tube, a clotted sample or contamination with heparin. The laboratory may request another sample if the first one is unsuitable.

Normal Range for Partial Thromboplastin Time (PTT) Test

PTT results are reported in seconds. The normal range for partial thromboplastin time (PTT) is around 25 to 35 seconds.

Results can be provided as:

• Normal PTT: Blood clots normally, within the laboratory’s reference range (approx. 25-35 secs).
• Prolonged PTT: Blood clots slower or takes longer than expected.
• Shortened PTT: Blood clots faster than the expected reference range and may need evaluation depending on the clinical situation.

A PTT result must be interpreted alongside other coagulation tests, medical history, symptoms, and medications.

“The exact range can differ between laboratories because reagents, instruments and testing methods vary. The range printed on the individual laboratory report should be used for interpretation.”

What Happens if Test Results Show Abnormal Findings?

Abnormal Partial Thromboplastin Time (PTT) Test results may indicate a problem affecting the body’s blood-clotting process. It may show that the sample either clotted faster or slower. The importance of an abnormal result depends on how much the result is changed and the patient’s overall health.

High or Prolonged PTT

A prolonged PTT means blood took more time to clot. Possible causes include:

• Haemophilia A or B
• Von Willebrand disease
• Clotting factor deficiencies, such as VIII, IX, XI or XII (Factor XII deficiency can produce prolonged PTT, while the person may not have abnormal bleeding issues)
• Heparin treatment
• Liver disease
• Disseminated Intravascular Coagulation (DIC)
• Lupus anticoagulant (May prolong PTT during test but can increase the risk of blood clots in the body)
• Specific clotting factor inhibitors
• Vitamin K deficiency (in some cases)
• Certain types of leukaemia

A prolonged PTT may increase the risk of abnormal bleeding, depending on the underlying cause.

Low or Shortened PTT

A shortened PTT is not commonly associated with a specific disease. It can occur due to changes in levels of clotting factors or other factors affecting coagulation. For example, factor VIII may be increased in inflammation, pregnancy, or other acute illnesses.
Sometimes it’s not because of a medical condition but due to collection or processing of the sample.
A short PTT alone cannot diagnose a blood-clotting disorder. Your healthcare provider will decide whether the test needs to be repeated or investigated further.

Your healthcare provider may consider additional testing if the result is unexpected or if symptoms are suggesting a clotting disorder, such as:

• Prothrombin Time (PT) Test
• International Normalised Ratio (INR)
• Complete Blood Count (CBC)
• Fibrinogen Test
• D-Dimer Test
• A PTT Mixing Study
• Clotting Factor Tests
• Lupus Anticoagulant Testing
• Von Willebrand Factor Testing

Understanding PTT Results & Next Steps

A person receiving heparin is expected to have a longer clotting time. The required treatment is not the same as the normal range and must be set by the healthcare team. A patient should never change a heparin dose based only on a laboratory result without medical guidance.

A result within the normal range does not rule out every bleeding disorder. Some conditions, including factor XIII deficiency and mild forms of certain clotting-factor disorders, may not produce an abnormal PTT result.

A medical professional decides additional testing and treatment based on the person’s medical history, symptoms and risk of bleeding.

Looking for a Reliable Assessment of Your Blood Clotting? 

Schedule your Partial Thromboplastin Time (PTT) test today at Genex Laboratory! We provide accurate results and top-notch laboratory support.