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.