Underfilled Citrate and Delayed EDTA From a Rural Clinic
At 09:40, a courier delivers two tubes from a rural clinic: a 3.0 mL light-blue sodium citrate tube filled to 2.1 mL and a 2.0 mL K2EDTA tube filled to 1.4 mL. The requisition lists PT/INR and a CBC with differential. The draw time was 06:10, and the tubes traveled at ambient temperature (22°C). The clinic's centrifuge is broken, so plasma has not been separated. The CBC analyzer requires at least 1.0 mL, and the coagulation analyzer requires a 9:1 blood-to-citrate ratio with a 3.0 mL fill line. The patient is a 74-year-old man on warfarin, and the INR result will determine tonight's dose. The clinic asks whether the samples can be run as-is and offers to recollect if needed. You must decide what is acceptable and what must be rejected.
1. Evaluate the acceptability of each tube. Which result or results can be reported, and which require recollection? Explain the scientific basis.
Read the worked answer
Reject the light-blue tube. A 3.0 mL citrate tube filled to 2.1 mL is 70% full; the blood-to-citrate ratio is altered because the citrate volume is fixed, so the plasma is over-anticoagulated. This falsely prolongs PT/INR and is unacceptable for warfarin dosing. The EDTA tube is acceptable for CBC: 1.4 mL exceeds the analyzer's 1.0 mL minimum, and 3.5 hours at 22°C is within typical EDTA stability for a CBC.
Run the CBC, but do not report the PT/INR. Because the INR determines tonight's warfarin dose, notify the clinic immediately and request a recollect in a correctly filled 3.0 mL citrate tube. Do not run the underfilled tube or mathematically correct the result. If the patient cannot be recollected today, the clinician must decide on dose management without the INR, knowing the result is unavailable.
2. If the EDTA specimen is acceptable, describe how you would process and release the CBC, including any findings that would still require a recollect.
Read the worked answer
Mix the EDTA tube by gentle inversion, verify label and volume, and run the CBC on the analyzer. Review automated flags and, if platelets are low or the histogram is abnormal, examine a stained smear for platelet clumping, giant platelets, or fibrin. If clumping is present, the CBC is not reliable; request a recollect, preferably in citrate or another anticoagulant per lab protocol.
Also check for hemolysis if the specimen is hemolyzed, because hemolysis can interfere with some parameters. Release the results with the draw time and receipt time documented. If the white cell differential is flagged or the delay exceeds the lab's stability limit, recollect. Do not delay the CBC unnecessarily; the 3.5-hour delay is acceptable, but smear review is the safeguard.
3. What would you document and communicate to the clinic, and what corrective action would you recommend?
Read the worked answer
Document the rejection reason, fill volume, draw and receipt times, and the notification to the clinic, including the name and time of the person notified. Send a written rejection report and request a recollect before the next warfarin dose.
Recommend corrective action: use a 3.0 mL citrate tube and fill to the line; if using a butterfly, draw a discard tube first; do not use a partially filled tube; centrifuge and separate plasma within the lab's stated window. Offer retraining on citrate tube fill and handling. Follow up to confirm the recollect arrives. If the clinic repeats the underfill, escalate to the lab supervisor. Keep the communication professional and focused on patient safety, because the INR result directly affects anticoagulant dosing.