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Coagulation Studies

Prothrombin Time (PT)

Normal range 11–13.5 seconds. Specimen: Plasma (sodium citrate).

Also known as: pro time.

11–13.5 secondsCritical: read below

Reference range

Conventionalseconds
1113.5
SpecimenPlasma (sodium citrate)
Conventional range11–13.5 seconds
SI range11–13.5 seconds
Conversion factor×1 (conventional → SI)
Critical value> 30 seconds (marked bleeding risk)
PanelCoagulation Studies

Convert any Prothrombin Time (PT) result between units on the unit converter.

What is the normal range for Prothrombin Time (PT)?

The standard teaching reference range for Prothrombin Time (PT) is 11–13.5 seconds. This value is measured in plasma (sodium citrate).

A commonly taught critical (panic) value is > 30 seconds (marked bleeding risk). Critical results are reported to the provider immediately under your facility's policy.

Source: Adult reference values compiled from Pagana & Pagana, Mosby's Diagnostic and Laboratory Test Reference, and Fischbach & Dunning, A Manual of Laboratory and Diagnostic Tests. Reference ranges vary by laboratory, method, age, sex, and population — always use the range printed on the actual result.

Above the range

Common causes of a high Prothrombin Time (PT)

  • Warfarin therapy
  • Vitamin K deficiency
  • Liver disease
  • DIC

Below the range

Common causes of a low Prothrombin Time (PT)

  • Vitamin K excess
  • Some clotting states

At the bedside

Nursing considerations

  • Evaluates the extrinsic pathway and monitors warfarin (reported as INR).
  • Assess for bleeding when prolonged; have vitamin K available as ordered.

Study aid

Your notes on Prothrombin Time (PT)

Same panel

More Coagulation Studies tests

Activated Partial Thromboplastin Time (aPTT)25–35 secondsBleeding Time2–7 minutesD-Dimer< 0.5 (negative) µg/mL FEUFibrinogen200–400 mg/dLInternational Normalized Ratio (INR)0.8–1.1 (off anticoagulation) ratioThrombin Time14–19 seconds