Blood collection and testing should be performed whenever possible after discontinuing NOAC treatment (4–5 days); if this is not possible, results should be interpreted cautiously.
NOACs are characterized by a quick onset of action and a short half-life. These drugs reach peak levels in plasma approximately 2 hours after ingestion and trough levels after 12 or 24 hours for those drugs administered twice or once daily, respectively. The associated consequence is that the interpretation of testing for NOAC requires accurate knowledge of the time lapsed between the administration of the last dose of medication and blood specimen collection.
Plasma or serum can be used for liquid chromatography-mass spectrometry/mass spectrometry. A plasma blood specimen should be collected in an evacuated test tube containing 3.2% sodium citrate (blue top tube). A platelet-poor specimen must be processed within 4 hours of collection. Centrifugation protocols to remove platelets from whole blood include the commonly applied protocol of centrifuging whole blood at 2,500 g for 15 minutes, which will deplete cells and part of the platelets. A second centrifugation step at 2,500 g for 15 minutes of the supernatant depletes most residual platelets (PFP, platelet-free plasma). Another method of using single-step centrifugation, platelet-poor plasma, is obtained by centrifugation of whole blood at 5,000 g for 20 minutes protocol.
For thrombin time testing (dabigatran), plasma samples are stable for 4 hours at room temperature. Specimens for dabigatran not tested within 24 hours of collection should be frozen.
After cell separation, plasma specimens for factor anti-Xa NOACs can be stored at ambient temperature for 4 hours, but refrigeration is unacceptable. Specimens can be frozen for up to one month, and frozen plasma can undergo three freeze-thaw cycles.
Unacceptable serum or plasma specimens include grossly hemolyzed specimens because of potential coagulation factor activation and chromogenic assay interference. In addition, serum or plasma that is grossly icteric (yellow) is not suitable for laboratory coagulation studies because the presence of bilirubin may interfere with chromogenic coagulation assays.
Urine Specimens
The DOAC Dipstick® (DOA SENSE) is the first point-of-care testing system that can detect reliably and accurately whether a patient has taken NOACs in critical situations.
The DOAC Dipstick is a diagnostic urine test strip intended for the qualitative detection of the absence or presence of dabigatran, apixaban, edoxaban, and rivaroxaban in human urine by visual identification of colors.
