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Prothrombin Time (PT) with Prothrombin Time Index (PTI) – Tetramethylbenzidine (TMB) Substrate Method

Published: August 9, 2026Updated: August 16, 2026

This test measures how long it takes for your blood to clot, using a specific chemical reaction to assess certain blood clotting factors. It helps check for bleeding disorders or liver issues.

Quick summary

["PT with PTI helps evaluate blood clotting function and liver health by measuring clot formation time and factor activity."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
46717-5
Short code
TT imm Bovine Thrombin PPP
Synonyms
TT imm Bovine Thrombin PPP
Category
chemistry
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
coag-thrombin-induced-factor-substitution-immediately-after-addition-of-bovine-thrombin
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test to diagnose or monitor conditions like liver disease, bleeding disorders, or to check if blood thinners are working properly. It’s also used before surgeries or procedures that could affect bleeding.

What Does the Test Involve?

A small blood sample is taken from your arm and sent to a lab. The blood is mixed with a special reagent that triggers a clotting reaction. The time it takes for a clot to form is measured, and the PTI reflects the relative activity of clotting factors compared to a standard.

What Are Common Conditions Monitored?

Elevated PT times may indicate liver problems (like cirrhosis), vitamin K deficiency, or certain blood clotting disorders. Low PT times could suggest overuse of blood thinners (like warfarin).

What Should You Know Before the Test?

Avoid taking vitamin K supplements or certain medications (like warfarin) for 2–5 days before testing, as they can affect results. If you’re on blood thinners, follow your doctor’s instructions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

PT with PTI (TMB)

Frequently asked questions

How long does it take to get results?
Results are typically available within 24 hours, depending on lab processing times. Your doctor will discuss them with you during your follow-up.
Does this test require fasting?
No fasting is needed for this test. However, if you’re on blood thinners, follow your doctor’s specific instructions to ensure accurate results.
Can I drink alcohol before this test?
Moderate alcohol use is usually fine, but heavy drinking may affect liver function, which could influence PT results. Avoid excessive alcohol for 24 hours before testing if possible.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy