From our colleague and frequent contributor Heather DeVries, Indiana University Health. Greetings George! One of our labs contacted me about PTT specimens coming from outpatient clinics, where they do not have centrifuges. Before coming into our system, this lab did a small study (30 specimens) to validate 24-hour stability of nonheparinized specimens for PTT testing. This goes against everything I know about the PTT, but when it comes to outpatients, I can see why they did the study. I wonder how other large systems address this? We do have a fair number of specimens that we cancel from outreach during the evening shift–the whole blood specimens are couriered here, but greater than 4 hours old when received. Thanks, Heather.
Hello, Heather, this is a challenging issue. I’m with you, uncentrifuged specimens for the PTT assay must be maintained at room temperature, spun, and analyzed within 4 hours to avoid deterioration in von Willebrand factor, factor VIII, factor IX, and protein S activities. The documentation is probably on your shelf or in your computer: Clinical and Laboratory Standards Institute (CLSI). Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays: Approved Guideline-Fifth Edition. CLSI document H21-A4. The CLSI guideline is based on solid research, especially data reported in Adcock DM, Kressin IX, Marlar RA. The effect of time and temperature on routine coagulation tests. Blood Coag Fibrinolysis 1998; 9: 463–70 and reviewed in Favaloro EJ. Preanalytical variables in coagulation testing. Blood Coag Fibrinolysis 2007; 18: 86–9. Further, specimens from patients on unfractionated heparin must be centrifuged and analyzed within one hour, whereas specimens for PT are good unspun and held at ambient temperatures for up to 24 hours.
I would distrust a 30-specimen sample, as it may not provide enough abnormals to reach a generalizable conclusion. I’d suggest you help your small outpatient clinics to equip themselves with an inexpensive but reliable desktop centrifuge, which would enable them to follow the CLSI guideline.
One additional reference I recommend for your shelf is Ernst DJ, Ernst C. The Lab Draw Answer Book, Second Edition. Center for Phlebotomy Education, 2017. The book offers authoritative specimen collection standards in a Q&A format from Catherine and Dennis Ernst, your fellow Indianians, and international blood collection experts.
An update for this post: our
An update for this post: our pathologist is not in favor of performing this study. Smaller facilities may benefit from it, but with the scope of our patient population over a large portion of the state, there are too many variables that we could not control, such as requests for add-ons. How do you explain which specimens are acceptable for extended stability (an outreach/outpatient specimen) vs the ones that are not (hospitalized patients). What if the patient has a transient lupus anticoagulant – how would that affect the specimen stability? There are too many unknown variables to us to really keep good control over the situation. I was kind of sad, but relieved at the same time!
Added by Geo: Thank you, Heather, all are important considerations. I would suggest assisting your satellites with the purchase of small desktop centrifuges, there are many high-quality ones available.
Hello, again, Heather, and a
Hello, again, Heather, and a big thank you to Dr. Favaloro, who referenced his publication with Drs. Lippi and Adcock; Adcock Funk DM, Lippi G, Favaloro EJ. Quality standards for sample processing, transportation, and storage in hemostasis testing. Semin Thromb Hemost. 2012;38:576–85. The article reviews some convincing evidence for extending the storage time for unspun non-heparin whole blood specimens for PTT to 6, 8, or even 24 hours. Given this information, I agree with Heather, there would be value in conducting a study with her satellite facilities using a selected sample of normal and abnormal specimens to establish a reasonable storage time. Extension beyond four hours would relieve smaller facilities of the need to follow the restrictive four-hour time limit.
All right…I have another
All right–I have another question. Our system is getting together a game plan on how to attempt a stability study for nonheparinized PTTs. I mentioned already that one site has done a small study, but it involved a different analyzer. Would those results be valid in our new study? Does this need to be instrument/reagent specific? Either way, we are thinking of starting with the four major hubs, and collecting data each of them. That way it will truly be a system study, and not based off of one site.
This is fascinating to me,
This is fascinating to me, and I can’t wait to see what comes out of it all! Thank you, both, for your insight. I’ll keep you posted!
Can I recommend two excellent
Can I recommend two excellent additional references (personal bias acknowledged!):
1. Adcock Funk DM, Lippi G, Favaloro EJ. Quality standards for sample processing, transportation, and storage in hemostasis testing. Semin Thromb Hemost. 2012;38:576–85.
2. Lippi G, Salvagno GL, Montagnana M, Lima-Oliveira G, Guidi GC, Favaloro EJ. Quality standards for sample collection in coagulation testing. Semin Thromb Hemost. 2012;38:565–75.
Dot Adcock is the lead author in the first paper, which actually addresses many of the issues with which labs struggle in relation to sample processing. Importantly, the recommendations of the 2008 CLSI guidelines are compared with other published literature (including in a nice summary table). In brief, some publications support the stability of non-heparinised whole blood for APTT testing for up to 24 hours. Indeed, our own centre accepts such samples for testing, although also acknowledging that earlier is always better! But pragmatically, the geographical separations from collection facilities and the difficulties of setting up centrifuges in all collection facilities prevents this on occasion.
Your response is so helpful,
Your response is so helpful, as usual! Thank you, George. I will pass along this information to our satellite hospitals. The outreach and outpatient specimens for coagulation testing get lost in the mix of hematology and chemistry, and I am certain that coag specimen integrity needs some close attention.