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Underfilled Tubes

I received this question on September 15 from Carolina Vilchez:

I am Carolina Vilchez, an Adjunct Professor at Rutgers-SHP, and a Clinical Educator at The Valley Hospital in Ridgewood, NJ. I was wondering if you would kindly answer a few questions about coagulation blood sample collection and management.
We have been having some issues in the laboratory with seasoned staff as well as new staff members and debates about QNS samples for routine coagulation tests. Certain staff members will run slightly underfilled samples for routine coagulation tests, while newer staff members cancel those samples as QNS and request new draws.
We follow CLSI guidelines and other resources to create our policies. Currently, our policies state that citrated blood specimens for coagulation should be rejected if they are underfilled (under the minimum fill line), which we assume is 90%.  According to the International Council for Standardization in Hematology (ICSH) recommendations for the collection of blood samples for coagulation testing, blood with <80% of nominal filling volume should be rejected by the laboratory and should NOT be analyzed. Do you suggest that we continue to enforce the <90% rejection rule or is it advisable to use the 80-90% rule in an effort to avoid over-canceling samples and requesting new draws?
We are also finding out that the personnel are evaluating a sample for sufficient quantity only after the specimen was spun down in the centrifuge. I was under the impression that this incorrect practice and that samples should be evaluated for quantity before they are placed in the centrifuge.
I appreciate you taking the time to read my questions. Any advice that you can provide on this would be greatly appreciated.
With Kind Regards,
Carolina Vilchez, MS, MLS (ASCP)H
Adjunct Assistant Professor
Medical Laboratory Science Program

After consulting with expert Bob Gosselin, I replied…

  • Your “instructions for use” [IFU] should be based on the manufacturer’s specifications. I recall that BD establishes anything less than 90% as a short draw.
  • It’s off-label, but since short draws raise the AC/blood volume ratio, potentially prolonging PTs and PTTs, we think a normal “routine” PT or PTT on a short draw is reportable.
  • Whether the specimen volume is estimated pre- or post-centrifugation is moot.

Please post your comments below, we’d like to confirm that we are giving the best advice.

Comments (1)
Specimen Management
Sep 22, 2022 3:11am

I would agree with Bob
I would agree with Bob Gosselin. The standard cut-off tends to be within 90% of tube fill. However, major effects on PT and APTT tend not to occur until <80% fill. In theory, you should follow the manufacturer recommendations in their IFU, but if permissible in your locality, and if validated by your lab, you could use the ICSH guidelines to go to 80%, especially relevant in pediatrics if it avoids unnecessary recollections. The line on most tubes reflects the ‘100%’ fill line, not the 90% fill line. It is easy to estimate the 90% and 80% fill volumes – just fill an emptied blood collection tube to 80% and 90% of the fill volume with water, mark the fill volume and take a photo; replicate in the lab documentation with same dimensions for benefit of staff. For example, for a 5 mL collection tube, 80% and 90% would be 4 mL and 4.5 mL volume respectively. You have to balance the requirement for accurate testing with legal and accreditation requirements and patient/clinician inconvenience. As under-filling generally causes prolongation of clotting times, a normal clotting time on an under-filled tube could be acceptable, since one would predict the correctly filled tube would also be normal, and thus no clinical difference.

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