APTT test (activated partial thromboplastin time) (ADTL)
Also known as: APTT
According to the MedlinePlus medical encyclopedia; the range depends on the reagents and method the laboratory uses, so the exact limit is on your report
- Updated
- 2026-09-30
- Every number with its source
What the APTT test shows
The activated partial thromboplastin time (ADTL in Lithuanian, and often called by the international abbreviation APTT or PTT) is a blood clotting test that shows how long it takes blood plasma to clot after the so-called intrinsic clotting pathway has been activated. Clotting depends on a series of proteins — the clotting factors — which act one after another like a chain. If even one of them is missing or does not work properly, the blood clots more slowly than usual and the APTT is prolonged. The test is often done together with the prothrombin time (PT, INR), which assesses the other — the so-called extrinsic — clotting pathway; together they help the doctor to narrow down which particular clotting factor may be disturbed. APTT is also used to monitor treatment with heparin, a medicine that reduces the clotting of blood, because heparin acts on exactly those factors that this test measures.
The result is reported in seconds. According to MedlinePlus, the test is used to diagnose bleeding disorders, to monitor heparin treatment and to assess the risk of bleeding before an operation.
The reference range
| Group | Range, s | Source |
|---|---|---|
| General guide According to the MedlinePlus medical encyclopedia; the range depends on the reagents and method the laboratory uses, so the exact limit is on your report | 25–35 | MedlinePlus Reviewed 2025-02-03 |
According to the MedlinePlus medical encyclopedia, the APTT is usually 25–35 seconds. This is a general guide rather than a universal limit: the range depends on the reagents and method the laboratory uses, so you will find the exact range of your own laboratory on the report sheet, next to your result.
When the test is done
- Before an operation or an invasive procedure, when the risk of bleeding needs to be assessed
- When bruises of unclear origin appear, when bleeding from wounds or from the nose takes a long time to stop, or when the gums bleed
- During treatment with heparin — to monitor and adjust the dose
- When an inherited bleeding disorder is suspected, for example haemophilia A or B, or von Willebrand disease
- When an autoimmune condition related to clotting is suspected, for example lupus anticoagulant
- Together with the prothrombin time (PT/INR), when the overall state of the clotting system is being assessed
How to prepare
- No special preparation is needed for an APTT test — fasting before the test is not required
- It is important to tell your doctor about any medicines you take that affect blood clotting, because they can affect the result
A prolonged APTT
A prolonged APTT means that the blood clots more slowly than usual. According to MedlinePlus, this may indicate an inherited bleeding disorder, liver disease, vitamin K deficiency, a shortage of certain clotting factors or too much heparin in the blood. The result is always assessed together with other clotting tests and the clinical picture.
- Haemophilia A or B — an inherited deficiency of individual clotting factors
- Liver disease, because most clotting factors are made in the liver
- Vitamin K deficiency
- Von Willebrand disease — an inherited clotting disorder
- Too much heparin (a blood-thinning medicine) in the blood
- Some forms of leukaemia
- Autoimmune conditions, for example lupus anticoagulant
Symptoms that can accompany it: bleeding that takes a long time to stop after small cuts; joint pain or swelling.
What to discuss with a doctor: discussing the result with a doctor together with the prothrombin time (PT/INR) and other clotting tests; if blood-thinning medicines are being taken, discussing with the doctor whether the dose needs adjusting; the family history of inherited bleeding disorders; and liver function tests, if liver disease is suspected.
A shortened APTT
A shortened APTT means that the blood clots faster than usual. According to MedlinePlus, this can be an early stage of disseminated intravascular coagulation (DIC), a raised amount of clotting factors during inflammation, pregnancy or cancer, and also some cases of ovarian, colon or pancreatic cancer. Such a result is assessed together with other clotting tests.
- An early stage of disseminated intravascular coagulation (DIC)
- A raised amount of clotting factors due to inflammation, pregnancy or a cancer
- Advanced forms of ovarian, colon or pancreatic cancer
Symptoms that can accompany it: signs of excessive clotting — pain, swelling and warmth in the limbs.
What to discuss with a doctor: discussing the result with a doctor together with other clotting and inflammation markers; if a cancer is known, discussing the monitoring of clotting risk with the treating doctor; and repeating the test so that the change over time can be seen.
Related indicators
- Prothrombin time (PT/INR) — the other clotting pathway
- D-dimer
- Fibrinogen
- Platelets
- Vitamin K
Full site in Lithuanian: proactiva.app
Frequently asked questions
›What is the normal range for an APTT (PTT) test?
According to the MedlinePlus medical encyclopedia, the APTT is usually 25–35 seconds. This is a general guide: the range depends on the reagents and method the laboratory uses, so you will find the exact range of your own laboratory on the report sheet, next to your result.
›How does APTT differ from the prothrombin time (PT/INR)?
APTT assesses the intrinsic clotting pathway, while the prothrombin time (PT, often expressed as INR) assesses the extrinsic one. The two tests are often done together, because together they help the doctor to work out which particular clotting factor may be disturbed.
›Why is APTT checked during treatment with heparin?
Heparin is a blood-thinning medicine that acts on exactly those clotting factors that APTT measures. That is why this test is used to monitor whether the heparin dose is suitable and whether the blood is clotting too slowly or too quickly.
›Do I need to fast before an APTT test?
No — according to MedlinePlus, no special preparation is needed for this test. It is worth telling your doctor about any medicines you take that affect blood clotting, because they can affect the result.
›What does a prolonged APTT mean?
A prolonged APTT shows that the blood clots more slowly than usual. There can be several causes — from inherited bleeding disorders to liver disease or vitamin K deficiency — so the result has to be discussed with a doctor together with other tests.
›Is the APTT test different from PTT?
No, it is the same test. APTT (or PTT) is the international abbreviation of the English “activated partial thromboplastin time”, while ADTL is the Lithuanian name for the same test.
Sources
Related markers
This site is not an emergency service. If severe chest or head pain, breathlessness, confusion, difficulty speaking, heavy bleeding or another acute problem has come on suddenly — do not wait for tests, call 112.
This information is not a diagnosis and does not replace a consultation with a doctor. Reference ranges depend on the laboratory, your age and sex — always compare your result with the range printed on your own report.