Can this result diagnose a condition on its own?

No. Laboratory results are interpreted with symptoms, medical history, specimen conditions and related tests.

Which reference range should I use?

Start with the performing laboratory's own reference interval; clinical cutoffs, when relevant, are separate sourced thresholds used for a specific purpose.

When should I discuss the result with a healthcare professional?

Results that are clearly outside range, persistent, symptomatic or unexpected should be reviewed by a healthcare professional.

Information about a laboratory test

aPTT (PTT): Low Result: What Does It Mean?

A shortened aPTT can occur with inflammation, pregnancy, some cancers or increased clotting factors and is not a diagnosis of a clotting disorder by itself.

Test summary

Test name: aPTT (PTT)
Abbreviations: aPTT, PTT
Category: Coagulation
Panel: Coagulation Assessment
Specimen: Citrated plasma
Common units: seconds

What does the test measure?

The aPTT (PTT) test measures clotting time and the function of factors mainly in the intrinsic and common coagulation pathways.

Why is the test ordered?

It may be ordered to investigate abnormal bleeding or clotting, assess coagulation before procedures, or monitor selected anticoagulant therapies.

Information about a low result

A shortened aPTT can occur with inflammation, pregnancy, some cancers or increased clotting factors and is not a diagnosis of a clotting disorder by itself.

Information about a high result

A prolonged aPTT can occur with deficiencies or dysfunction of certain clotting factors, heparin, liver disease or lupus anticoagulant, among other causes.

Reference and clinical context

Start with the performing laboratory's reference interval, unit, specimen type and method. Numeric information on this page is stored as sourced example intervals or clinical thresholds.

Reference range 1

>= 25 – <= 35 seconds

Population: Adults / general laboratory example
Age range: 18
Specimen: Citrated plasma

Example aPTT/PTT reference interval

This is sourced reference/clinical-context information and should not be used alone as a diagnosis or treatment decision. The laboratory report, medication use and clinical context take priority.

Reference ranges may vary by laboratory, method used, age, sex, pregnancy status, and clinical context. The reference range on your own laboratory report takes precedence.

Interpretation notes

aPTT assesses different coagulation factors from PT. With lupus anticoagulant, prolongation in the test tube does not necessarily mean a bleeding tendency in the body.

Related specialties

Hematology
Internal Medicine
Emergency Medicine

Frequently asked questions

Sources

Fibrinogen blood test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2025 · Fibrinogen purpose and example 200–400 mg/dL reference interval · Verified: Aug 12, 2026
D-Dimer Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · D-dimer use in clot assessment and non-thrombotic causes of elevation including pregnancy · Verified: Aug 12, 2026
Prothrombin Time Test and INR (PT/INR) — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · PT/INR purpose, anticoagulation and coagulation interpretation · Verified: Aug 12, 2026
Partial Thromboplastin Time (PTT) Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2026 · aPTT/PTT purpose, prolonged and shortened result context · Verified: Aug 12, 2026
Partial thromboplastin time (PTT) — U.S. National Library of Medicine (MedlinePlus)
Government medical encyclopedia · 2025 · Example 25–35 second PTT interval and laboratory variability · Verified: Aug 12, 2026