From Anita Elledge, MT (ASCP), blood bank/coagulation supervisor, Sierra Vista Regional Health Center, AZ: Our coagulation testing is done on a Stago Compact instrument. The linear range is 20–200 s for the activated partial thromboplastin time (APTT, PTT). We have a policy that any PTT result <22 s must be redrawn, not just rerun the same sample, because it is said that a low PTT result should not occur and is almost always due to a bad collection. I can’t seem to find any documentation that confirms the < 22 s result being a point for this “recollect.” Can you give me a resource for information or any further help with this?
Category: Specimen Management
From Soakimi Pouhila, Auckland District Health Board, New Zealand: Hi George, any ideas on the stability of rivaroxaban in citrate samples?
Hello, Soakimi Pouhila, and thank you for your question, which sent me to PubMed to see if anything has been published on rivaroxaban stability. My search was fruitless, so I’m posting your question to attract comments from anyone with anecdotal experience. Let’s hope we get an answer soon.
From Crystal Azevedo, “Are there any substances known to interfere with the neutralization of heparin by the Dade (Siemens) Hepzyme product? We recently worked on a patient sample that I am told had absolutely NO heparin in it, yet the PTT decreased from >200 seconds to 89 seconds after treatment. Thanks!”
George received a note from a colleague who has three separate specimens from a patient with prolonged partial thromboplastin times (PTTs) that further prolong as they stand at ambient temperature over periods of several minutes, for instance, 57s, 151s after 20 minutes, and 174s after 2 hours. Mixing studies consistently correct. They’ve tested them on both electromechanical and optical instruments. No anticoagulants, the serum protein electrophoresis is normal, and the factor V level is 162%. George shared the question with several experts while attending the ASCLS/AACC annual meeting in Houston, and so far we have no answers. Any ideas?
From Diane Belliveau, Catholic Medical Center, Manchester, New Hampshire: Hi George, we have a special care nursury. I am looking for help in specimen handling/volumes for these special patients. Are there any new products for coagulation specimen collections on babies?
Hi, Diane, the only 3.2% sodium citrate tube available for low-volume collection, 1 mL, is the Greiner Bio-one MiniCollect® tube, catalogue number 450413. The description, however, carries this notation, “MiniCollect Coagulation Tubes are for use with venous blood only.” There appear to be no capillary collection devices for coagulation.
If any participant has a recommendation for collection from newborns, please comment below.
Here is a message about the dilute Russell viper venom time assay (DRVVT) for lupus anticoagulant (LA) from international expert Thomas Exner, HAEMATEX, Sydney, Australia:
It was a pleasure to meet you at the International Society on Thrombosis and Haemostasis (ISTH) meeting recently. I would like to respond an interesting question raised on July 16, 2013 in your Fritsma Factor website. Best wishes.
From Michael Suter, MT (ASCP) SH Senior Clinical Scientist, Hematology, Peace Health Laboratories, Springfield, Oregon.
George, I am curious about your thoughts on how to best address the effect of high hematocrits (HCTs) on the quantitative latex D-dimer assays such as the Stago D-Di test. With high HCT samples, there is a relative decrease in plasma causing a relative excess of anticoagulant. With prothrombin time (PT) and partial thromboplastin time (PTT, APTT), it’s necessary to redraw the patient into a tube with a decreased amount of anticoagulant to normalize the plasma:anticoagulant ratio. You can’t simply correct mathematically for the excess anticoagulant, because the effect is more than dilutional and the test may end up measuring citrate anticoagulation instead of just the in vivo patient anticoagulation. Empirical studies were required to show that high HCT becomes significant above 55%.
From Barbara Caufield, Good Samaritan Hospital: We adjust the Na citrate volumes in coagulation tubes when the hematocrit (HCT) is > 55%. Do you recommend correcting for low HCTs? Can you tell me what formula you would use for a low HCT? At what HCT percentage do you recommend adjusting the sodium citrate? Thank you!