Lab tests
INR, PT and aPTT results explained
Clotting tests report how long a blood sample takes to clot under laboratory conditions, in seconds or as a ratio. Add your report below to see each line named and set against the range the laboratory printed.
Explain your coagulation test
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- 3. Read itSummary, table of results, terms and questions to ask.
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What you get
- PT, INR, aPTT and any other clotting results on separate rows.
- An explanation of why INR exists alongside PT.
- Any target or therapeutic range printed on the report restated as written.
- Questions to ask your anticoagulation clinic or doctor.
Lines you may see
- PT (prothrombin time)The time a sample takes to clot in one standard test, in seconds
- INRThe PT converted to a standard ratio so results can be compared between laboratories
- aPTTThe time a sample takes to clot in a second standard test
- FibrinogenA protein the body uses to form clots
- D-dimerA fragment released when a clot is broken down
What this tool cannot tell you
For people taking a blood thinner such as warfarin, the INR target is set individually by the clinician, and it is deliberately higher than the general range printed on a report. MedicDecode explains what the lines are. It never comments on doses. Do not change how you take an anticoagulant because of anything you read here; contact your clinic.
Common questions
What is the difference between INR and PT?
PT (prothrombin time) is measured in seconds and varies between laboratories. INR converts it into a ratio that means the same everywhere, which is why warfarin is monitored with INR.
What is a normal INR?
In people not taking a blood thinner it is about 1. If you take warfarin, your prescriber sets a higher target range for you, and the report may print it.
What is the difference between INR and aPTT?
They test different parts of the clotting process. INR follows warfarin and liver-related clotting factors; aPTT is used, for example, with heparin.
Why is my INR flagged high when I am on warfarin?
The printed range is usually for people not taking a blood thinner. Your own target range is set by your clinician and may be stated separately on the report.
Why report both PT and INR?
PT in seconds varies with the laboratory's equipment and reagents. INR adjusts for that so results from different laboratories mean the same thing.
Can it tell me whether my dose needs changing?
No. Only your anticoagulation clinic or doctor can decide that.
Words you may see on this report
Tap a word for its plain-English meaning, an example line and what it does not mean.
- INR (International Normalized Ratio)
INR is a standardised measure of how long your blood takes to clot, often used to check blood-thinning medicines such as warfarin.
- ALT (Alanine Aminotransferase)
ALT is an enzyme found mainly in the liver; when liver cells are irritated or damaged, more ALT leaks into the blood.
- AST (Aspartate Aminotransferase)
AST is an enzyme found in the liver, muscles, heart and other tissues; raised levels can signal stress or damage in one of these.
- Bilirubin
Bilirubin is a yellow substance made when old red blood cells break down; the liver processes it so it can leave the body.
- Creatinine
Creatinine is a waste product from normal muscle activity that the kidneys filter out, so its blood level helps show how well the kidneys work.
- CRP (C-Reactive Protein)
CRP is a protein made by the liver that rises quickly when there is inflammation or infection in the body.
- Culture and Sensitivity
A culture and sensitivity test grows germs from a sample to identify them, then checks which antibiotics can stop them.
- eGFR (Estimated Glomerular Filtration Rate)
eGFR is an estimate of how well your kidneys filter waste from your blood, calculated from a creatinine blood test plus details like age.
- Electrolytes
Electrolytes are minerals in the blood, such as sodium, potassium and chloride, that carry an electric charge and help the body work.
- ESR (Erythrocyte Sedimentation Rate)
ESR measures how fast red blood cells sink in a tube of blood over an hour; a faster rate can be a general sign of inflammation.
- Fasting Sample
A fasting sample is blood taken after you have had nothing to eat or drink except water for a set number of hours.
- Ferritin
Ferritin is a protein that stores iron; its blood level gives a good idea of how much iron the body has in reserve.
Medicines connected to this test
Their official labels mention this kind of test. Each is explained in plain English.
- Apixaban
A factor Xa inhibitor, a blood thinner medicine (anticoagulant)
- Clopidogrel
A platelet inhibitor of the P2Y12 type (a thienopyridine). It is a blood thinner that keeps platelets from sticking together.
- Diclofenac Sodium
A nonsteroidal anti-inflammatory drug (NSAID). The FDA class is not listed on the label.
- Medroxyprogesterone Acetate
A progestin hormone. The label describes it as a derivative of progesterone. The FDA pharmacologic class is not listed.
- Naproxen
a nonsteroidal anti-inflammatory drug (NSAID), which is a medicine that reduces pain, swelling, and inflammation
- Rivaroxaban
a factor Xa inhibitor, a type of blood thinner (anticoagulant)
- Warfarin Sodium
A blood thinner (anticoagulant) of the vitamin K antagonist type. The label says it acts by blocking vitamin K-dependent clotting factors.