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Reference intervals are vital for interpreting coagulation results. Current interval ranges have no upper age limit, although there is evidence that coagulation function changes with age. This study compared coagulation results from healthy people aged >60 years against adult reference intervals for routine clotting assays and thromboelastography (TEG) to determine if reference intervals are relevant to older adults.Samples from healthy blood donors aged >60 years (n=30 male, n=30 female) were tested by TEG® 6s, prothrombin time (PT), activated partial thromboplastin time (aPTT), and derived fibrinogen.All older donor-derived fibrinogen results were within the adult reference intervals, however levels were significantly higher in females. A proportion of TEG® 6s and aPTT results were not within the reference intervals. As populations around the world live longer, these findings question whether older adults require age specific coagulation reference intervals., (© 2020 by the Association of Clinical Scientists, Inc.)

The use of international biological standards during the last 30 years has proved extremely successful in promoting global harmonization of estimates between laboratories and methods. Experience has led to the identification of physical criteria essential for standards to be suitable for long-term use. High precision of liquid filling coupled with low residual moisture and oxygen and the use of sealed glass ampoules have been found consistent with homogeneous and stable International Standards (ISs). Most plasma coagulation factors and inhibitors are calibrated in International Units (IU), which are defined as the amount of analyte in 1 mL of normal pooled plasma. Adoption of the IU has provided clarity in the definition of normal and abnormal states and has facilitated dose calculation for replacement therapy. The assay of like-versus-like materials (e.g., concentrate versus concentrate) has been found to improve interlaboratory agreement and there are now both plasma and concentrate ISs available for many coagulation factors and inhibitors. Studies into the assay of recombinant factor VIII have indicated that additional measures, such as modifications to assay methodology, are necessary to reduce interlaboratory variability. This experience may prove valuable in the future, when we have to deal increasingly with the challenges to standardization associated with the products of bioengineering.

The fibrinogen clotting time (FCT) is a measure of thrombin activity, and is used to evaluate the potential thrombogenicity of prothrombin complex concentrates (PCC). We have defined end points for clot formation in this test which allow the measurement in PCC of thrombin concentrations as low as 0.001 IU/ml. The FCT of thrombin and PCC samples which did not contain antithrombin III (ATIII) were the same when measured at 20 degrees C or 37 degrees C. In the presence of ATIII (0.05 or 0.25 IU/ml), samples of PCC which were known to contain thrombin showed shorter FCT at 20 degrees C than at 37 degrees C. Inclusion of both ATIII (0.25 IU/ml) and heparin (4 IU/ml) in PCC ensured the complete inactivation of endogenous thrombin.