Measurement of heparin in plasma: influence of inter-subject and circadian variability in heparin sensitivity according to method.
Heparin was measured, with respect to standard curves prepared with normal pooled plasma, by five methods (APTT, thrombin time, one and two stage coagulation, anti-factor Xa and chromogenic anti-factor Xa) after addition at three concentrations to plasmaprepared from normal young volunteers, hospitalized patients with malignancy and geriatric patients. By the APTT and TT, differences in sensitivity were observed at 0.4iu heparin/ml corresponding to an apparent difference in heparin level of 10 and 14 fold between high and low responding individuals. Such large differences were not apparent by anti-factor Xa assay. A circadian difference in sensitivity was also observed in the patient group such that in samples taken at night, heparin levels were 30-50% higher on average when measured in the APTT and TT. Again, such large differences were not apparent by anti-factor Xa methods. In light of recent findings about the usefulness of anti-factor Xa methods for efficient monitoring of heparin, it is suggested that this conclusion may arise from the tendency for anti-factor Xa methods to determine actual concentrations of heparin.
D000328:Adult; D000368:Aged; D002940:Circadian Rhythm; D005069:Evaluation Studies as Topic; D005170:Factor X / Q000037:antagonists & inhibitors; D015951:Factor Xa; D006493:Heparin / Q000097:blood*; D006801:Humans; D007206:Individuality; D008722:Methods; D010314:Partial Thromboplastin Time; D013918:Thrombin Time
D005170:Factor X; D006493:Heparin; D015951:Factor Xa