Reflectance spectroscopy of clotting blood: a description of the time-dependent behavior.

CONTEXT: Research into whether cyclooxygenase-2 (COX-2) inhibitors affect thrombosis has been hampered by the lack of a specific assay. Erythrocytes modulate the effect of aspirin on platelets, which suggests that tests of whole blood clotting may be more sensitive. OBJECTIVES: To determine whether reflectance spectroscopy of clotting blood generates useful information about coagulation and whether it shows an effect of COX-2 inhibitors. DESIGN: A survey of 14 adults examined the range of phenomena demonstrated by reflectance spectroscopy. These phenomena were compared before and after treatment with a COX-2 inhibitor in 4 subjects. SETTING: Out-patient clinic. MAIN OUTCOME MEASURE: Reflected light intensity was measured from blood as it clotted in a cuvette thermostated at 37 degrees C. RESULTS: The survey of healthy adults showed that the time course of reflected light intensity is similar at all wavelengths and may be divided into 4 stages: a monotonic decrease, a sigmoidal increase, a linear region, and a terminal phase. Clot formation as determined by tube inversion occurs at the transition between the first and second phases; the sigmoidal increase cannot be due to fibrin polymerization. The terminal phase coincides with clot retraction. Similar results are obtained in native whole blood and in recalcified citrated blood. Cyclooxygenase-2 inhibitors have an intrinsic effect on the sigmoidal increase ex vivo (P <.001). CONCLUSIONS: Reflectance spectroscopy generates unique information about clotting blood. It is feasible to use anticoagulated blood to elucidate the events underlying the time course and to investigate the effects of COX-2 inhibitors.