Effect (or lack of it) of severe anemia on PT and APTT results.

Whether it is necessary to adjust the citrate volume in blood collection tubes for patients with anemia is unknown; however, the standard of care is not to adjust the volume. We compared the prothrombin time (PT) and activated partial thromboplastin time (APTT) test results of nonadjusted and adjusted citrate amounts in specimens from patients who are severely anemic. Samples were drawn into a 3.8% citrate volume, and if the hematocrit was less than 25% (0.25), additional samples were drawn into adjusted citrate tubes. The PT and APTT were run on 78 pairs of specimens, and the correlation coefficient was 0.98 for both assays. A statistically significant difference was noted between sample results collected in evacuated tubes in which the citrate volumes were adjusted to the hematocrit vs those in which it was not. However, when the difference between sets of values was plotted against the hematocrit, there was no correlation. There seems to be no need to change the standard practice for obtaining coagulation specimens into 3.8% citrate for patients who are anemic.