Discordant Point-of-Care INR in a Patient With Bleeding Symptoms
At a family medicine clinic, you are the phlebotomist running point-of-care INR testing for a 67-year-old man on warfarin. His last INR was 2.6, and today's POC meter result is 4.8. A repeat fingerstick on a different finger gives 2.9. The meter's daily quality control was performed at 08:00 and passed, but the test cartridge lot was opened 35 days ago and stored on the counter. The patient reports gum bleeding when brushing his teeth and a new bruise on his forearm. The clinic protocol says POC INR >4.0 requires same-day confirmation by the laboratory. The nurse asks if the 2.9 can be used to avoid a venipuncture because the patient is anxious. You must decide what result, if any, can guide today's warfarin dose.
1. How do you interpret the two POC results? What preanalytical and analytical factors could explain the discrepancy?
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The two POC results are discordant, and neither can be used alone to adjust warfarin. A change from 4.8 to 2.9 within minutes is larger than expected biological variation and suggests preanalytical or analytical error. Possible preanalytical causes include fingerstick technique with squeezing and tissue fluid, an insufficient drop, wrong finger, extreme hematocrit, or delayed testing. Analytical causes include a cartridge lot opened 35 days earlier and stored at room temperature, which may degrade reagents; meter or lot calibration drift; and temperature or humidity exposure.
The 4.8 is above the protocol threshold and the patient has bleeding symptoms, so the safer interpretation is that a high INR is possible. The 2.9 cannot be selected because it is convenient. The protocol requires lab confirmation when POC INR >4.0; that requirement is triggered by the first result.
2. What is your immediate action, and how do you explain it to the patient and nurse?
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Perform a venous draw for laboratory INR and send it promptly; do not delay because the patient is anxious. Explain that the fingerstick results disagree, that one is above the safety threshold, and that a venous result is needed before his warfarin dose is changed. Notify the clinician now, including the bleeding symptoms and both POC values.
Advise the patient to avoid aspirin and NSAIDs unless prescribed, apply pressure to bleeding gums, and seek care for severe bleeding. Do not tell him to skip or take warfarin; that is the clinician's decision. If the lab INR is also high, the clinician will manage reversal or dose reduction. If it is normal, document the discordance and investigate the meter. Keep the patient in the clinic until the clinician has reviewed the result if possible.
3. What QC, documentation, and follow-up steps should occur after the event?
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Repeat QC with a new cartridge lot and check the meter's storage and temperature log. Record the lot number, open date, QC results, both patient POC results, fingerstick sites, and the venous confirmation. File an incident report for the discordant POC result and possible reagent degradation. Notify the point-of-care coordinator and review whether cartridges may be stored on the counter for 35 days.
Retrain staff on fingerstick technique and lot dating if needed. Communicate the final lab result to the clinician and document the patient education. Follow up on whether the meter is removed from service until QC and calibration are verified. Do not discard the cartridge lot before investigation; retain it for review.