Quick facts
| Test | Range | Unit | Applies to |
|---|---|---|---|
| PT (prothrombin time)[1] | 11-14 | seconds | Teaching table, population not stated |
| INR[1] | 0.9-1.2 | No unit | Teaching table, population not stated |
| INR target on warfarin, DVT, PE or non-valvular atrial fibrillation[2] | 2.0-3.0 | No unit | DVT, PE or non-valvular atrial fibrillation |
| INR target on warfarin, mechanical mitral valve (tilting disk or bileaflet), or caged ball or caged disk valve[2] | 2.5-3.5 | No unit | Mechanical mitral valve (tilting disk or bileaflet), or caged ball or caged disk valve |
| aPTT (heparin's lab, for comparison)[1] | 20-40 | seconds | Teaching table, population not stated |
| aPTT target on heparin[4] | 1.5-2 | times normal | Full-dose heparin |
On warfarin, a high INR raises bleeding risk and a low one raises clot risk
- The warfarin label says an INR above 4.0 appears to add no benefit for most patients and is linked to a higher risk of bleeding.[2]
- Bleeding signs to assess and teach include gums that bleed after brushing, nosebleeds, unusual bruising, dark brown or red urine, red or black tarry stools, heavier menstrual flow, headache, dizziness and weakness.[2]
- A low INR can mean the blood clots too easily, with a risk of dangerous clots.[5]
INR is checked daily when warfarin starts, then every 1 to 4 weeks
Steady vitamin K intake keeps the INR steady
- Teach a normal, balanced diet with a consistent amount of vitamin K and no drastic diet changes, like suddenly eating far more leafy greens.[2]
Warfarin bleeding risk and INR monitoring are in the Antiplatelet and anticoagulant reasoning flashcard deck. Find the deck in the free app preview.
Open the free app previewHow it shows up on nursing exams
- Match the drug to the lab. Warfarin is monitored with PT/INR. Heparin is monitored with aPTT, and its label considers the dose adequate at an aPTT of 1.5 to 2 times normal.[2][4][5]
- PT results vary with the lab and the test method, so they are converted to an INR, which can be compared across labs.[5]
- If the patient is not taking warfarin, a high PT/INR can point to liver disease, vitamin K deficiency or a bleeding disorder.[5]
Practice question
A 71-year-old patient with non-valvular atrial fibrillation takes warfarin at home. The patient's target INR is 2.0 to 3.0. Today the INR is 4.6, and the patient reports that the gums bled after brushing this morning. Blood pressure is 134/82 mm Hg and heart rate 78/min and irregular. The evening warfarin dose is due. Which action should the nurse take first?
- A. Give the warfarin dose, then recheck the INR tomorrow
- B. Report the INR and bleeding gums before the dose
- C. Give vitamin K to bring the INR back into range
- D. Teach the patient to eat more green leafy vegetables
Show the answer and why
Correct answer: B. Report the INR and bleeding gums before the dose
- A. Incorrect. An INR of 4.6 is above the 2.0 to 3.0 target. The label says an INR above 4.0 appears to add no benefit for most patients and is linked to a higher bleeding risk, and the gums are already bleeding.
- B. Correct. The INR is above target, and gums that bleed after brushing are one of the bleeding signs the label tells patients to report. The provider adjusts warfarin based on the INR, so both findings go to the provider before the dose.
- C. Incorrect. Vitamin K can reverse warfarin, but the label bases that treatment on the INR level, any bleeding and the clinical situation. The provider decides after hearing the findings, so the report comes first.
- D. Incorrect. More vitamin K in food can lower the INR, but the label advises a consistent vitamin K intake and warns against drastic diet changes, like suddenly eating far more leafy greens. A diet swing is not how a high INR is managed.
Sources for this question: [2][5]
Memory hook: Warfarin watches the INR; heparin watches the aPTT.