Rare diseases · Sign or symptom
Prolonged prothrombin time
HP:0008151
What it means
Increased time to coagulation in the prothrombin time test, which is a measure of the extrinsic pathway of coagulation. The results of the prothrombin time test are often expressed in terms of the International normalized ratio (INR), which is calculated as a ratio of the patient's prothrombin time (PT) to a control PT standardized for the potency of the thromboplastin reagent developed by the World Health Organization (WHO) using the formula: INR is equal to Patient PT divided by Control PT.
The prothrombin time (PT) and the activated partial thromboplastin time (APTT) are the most requested tests to investigate patients with congenital or acquired coagulopathies and drug monitoring. They are defined as the time (seconds) needed to clot platelet-poor plasma upon addition of coagulation triggers, such as tissue factor in complex with phospholipids and calcium chloride (in the PT), or negatively charged phospholipids-activators and calcium chloride (in the APTT). They can hence be considered as global coagulation tests sensitive to deficiencies of many coagulation factors. In brief, they are both sensitive to factor X, V, II and fibrinogen, whereas the PT is only sensitive to factor VII deficiency and the APTT is sensitive to pre-kallikrein, high molecular weight kininogen (HMWK), factor XII, XI, IX and VIII deficiencies. Normal plasma in the PT clots approximately within 10-12 s upon triggering coagulation, and the normal reference range is (usually) narrow. PT results have been reported as clotting time, percentage activity, PT-ratio (patient-to-normal clotting time) and as international normalized ratio (INR). The INR scale has been devised to harmonize results stemming from different thromboplastins from patients on treatment with vitamin K antagonists. Some recommend abandoning the approach of using percentage activity to assess PR.
Rare diseases that can present with this32
Very common80–99%
5Common30–79%
14- 3-hydroxy-3-methylglutaric aciduria
- Acquired purpura fulminans
- Acquired von Willebrand syndrome
- Acute liver failure
- Acyl-CoA dehydrogenase 9 deficiency
- ALG12-CDG
- Congenital bile acid synthesis defect type 2
- Congenital factor VII deficiency
- HELLP syndrome
- Hepatoportal sclerosis
- Hereditary combined deficiency of vitamin K-dependent clotting factors
- Isolated biliary atresia
- S-adenosylhomocysteine hydrolase deficiency
- Scott syndrome
Sometimes5–29%
11- Abetalipoproteinemia
- Alacrimia-choreoathetosis-liver dysfunction syndrome
- Cirrhosis-dystonia-polycythemia-hypermanganesemia syndrome
- COG8-CDG
- Glycogen storage disease due to glycogen branching enzyme deficiency
- Hyperinsulinism due to short chain 3-hydroxylacyl-CoA dehydrogenase deficiency
- Kasabach-Merritt phenomenon
- Marburg hemorrhagic fever
and 3 more in this range
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Increased INR · Increased international normalised ratio · Increased international normalized ratio · Low factor II activity · Prolonged PT · Reduced factor II activity · Reduced prothrombin activity
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.