Home Biomarkers Activated Partial Thromboplastin Time

Activated Partial Thromboplastin Time

CBC Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: CBC

Overview

Activated Partial Thromboplastin Time (aPTT) is a blood test that measures how long it takes blood to clot via the intrinsic and common coagulation pathways. It evaluates the function of clotting factors VIII, IX, XI, XII and the common pathway factors (II, V, X and fibrinogen) and detects inhibitors to these factors. aPTT is used to investigate unexplained bleeding or bruising, monitor unfractionated heparin therapy, and screen for certain inherited bleeding disorders or acquired inhibitors (eg, lupus anticoagulant). Symptoms prompting testing include excessive bleeding after injury or surgery, spontaneous mucosal bleeding, or recurrent deep bruising. Newborns normally have longer aPTT; pregnancy and some inflammatory states may shorten it. Gender has minimal effect; elderly values can vary with comorbidities.

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Test Preparation

Overnight fasting is preferred but not mandatory
A duly filled coagulation requisition form (Annexure - CR/05) is mandatory for sample collection
Kindly provide complete clinical details and medication history or doctor's prescription
this information is important for correlation of your test results

Why Do I Need This Test

Profile: Included as part of coagulation testing (requested here within the CBC profile) - Symptoms: Unexplained bleeding, prolonged bleeding after procedures, easy bruising, mucosal bleeds, suspected clotting disorder - Conditions: Diagnoses/monitors hemophilia, factor deficiencies, lupus anticoagulant, DIC, liver disease; monitors unfractionated heparin therapy - Reasons for abnormal levels: Factor deficiencies, inhibitors (eg, antibodies), heparin, liver dysfunction, DIC, sample error - Biological meaning: Prolonged aPTT = delayed intrinsic/common pathway clotting; shortened aPTT = hypercoagulable tendency - Behaviors/lifestyle: Anticoagulant use (heparin), heavy alcohol use (liver disease), some antibiotics or supplements altering vitamin K or liver function - Family history: Known bleeding disorders (hemophilia, von Willebrand variants), history of thrombosis with antiphospholipid syndrome warrants testing

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Understanding Test Results

Values within 25–40 seconds are considered normal.
Mild prolongation (≈40–60 s) can indicate partial factor deficiency, low fibrinogen, early liver disease, therapeutic heparin, or presence of an inhibitor; correlate clinically and review medications.
Moderate to marked prolongation (>60 s) suggests significant factor deficiency, potent inhibitors (eg, lupus anticoagulant or factor VIII inhibitor), severe liver disease, DIC, or excessive anticoagulation and carries higher bleeding risk.
Very high values (>100 s) indicate severe coagulopathy and need urgent evaluation.
Shortened aPTT (<25 s) may reflect elevated factor VIII (acute phase/pregnancy) and can be associated with increased thrombotic risk.
Laboratory artifacts (improper tube filling, excess anticoagulant in the sample, hemolysis, lipemia) can also alter results; abnormal findings often prompt mixing studies to distinguish factor deficiency from inhibitors and correlate with clinical context.

Normal Range

25-40 seconds

FAQs

Q: What is activated partial thromboplastin time?

A: Activated partial thromboplastin time (aPTT) is a blood test that measures how long plasma takes to clot via the intrinsic and common coagulation pathways after adding an activator, phospholipid and calcium. It detects clotting factor deficiencies, inhibitors, liver disease, or disseminated intravascular coagulation, and is used to monitor unfractionated heparin therapy. Typical normal range is roughly 25–35 seconds (lab-dependent).

Q: What does it mean when your aPTT is high?

A: A high aPTT means your blood takes longer than normal to clot, reflecting abnormal intrinsic/common coagulation pathways. Causes include anticoagulant therapy (heparin), inherited factor deficiencies (eg, hemophilia), liver disease, disseminated intravascular coagulation, or lupus anticoagulant. Although prolonged aPTT usually signals bleeding risk, lupus anticoagulant can paradoxically raise clot risk. Ask a clinician for further testing and interpretation.

Q: What is the difference between PTT and aPTT?

A: PTT (partial thromboplastin time) and aPTT (activated PTT) both assess the intrinsic and common coagulation pathways. The key difference is that aPTT uses a contact activator and phospholipid, making it faster, more standardized and more sensitive than older PTT methods. Both evaluate factors VIII, IX, XI, XII, X, V, II and fibrinogen and are used to monitor unfractionated heparin; many labs report aPTT.

Q: What is a normal PTT and aPTT time?

A: Normal aPTT is about 25–40 seconds. PTT is often used interchangeably with aPTT and typically falls in the same range; some labs may report slightly different cutoffs. Always check your laboratory’s reference interval. Prolonged times can indicate clotting factor deficiencies, anticoagulant therapy, or liver disease; short times may suggest a hypercoagulable state.

Q: What conditions can cause prolonged aPTT?

A: Prolonged aPTT can result from anticoagulants (heparin, direct thrombin inhibitors), factor deficiencies (hemophilia A/B, factors XI or XII), acquired factor inhibitors (eg, acquired hemophilia), antiphospholipid antibodies (lupus anticoagulant), liver disease, severe vitamin K deficiency, DIC, paraproteinemia, or sample/technical errors. Some causes (factor XII deficiency) prolong aPTT without bleeding.

Q: How is an aPTT test different from a PT/INR test?

A: The aPTT measures the intrinsic and common coagulation pathways (factors XII, XI, IX, VIII and common factors X, V, II, fibrinogen) and is used to detect intrinsic pathway defects and to monitor unfractionated heparin. PT/INR assesses the extrinsic and common pathways (factor VII plus common factors) and is used to detect extrinsic defects and to monitor vitamin K antagonists like warfarin; INR standardizes PT.