MEASUREMENT OF HEPARIN CONCENTRATION IN WHOLE-BLOOD WITH THE HEPCON HMS DEVICE DOES NOT AGREE WITH LABORATORY DETERMINATION OF PLASMA HEPARIN CONCENTRATION USING A CHROMOGENIC SUBSTRATE FOR ACTIVATED FACTOR-X/

Measurement of circulating heparin concentration has been suggested to optimize anticoagulation during cardiopulmonary bypass. The Hepcon/HM S device (Medtronic HemoTec, Inc., Parker, Colo.) uses heparin/protami ne titration to quantitatively determine heparin concentration. Extens ive validation of this instrument is still lacking. Methods: Agreement between heparin concentrations measured by the Hepcon/HMS system and by laboratory determination was evaluated in 16 patients undergoing ca rdiac operations. For laboratory determinants, plasma heparin concentr ation was derived from the measure of anti-Xa activity by means of a c hromogenic substrate technique. The Hepcon/HMS instrument and cartridg es measured whole blood heparin concentration. Samples were analyzed 5 minutes after administration of heparin, 15 and 30 minutes after the start of cardiopulmonary bypass, 5 minutes after aortic unclamping, at the end of cardiopulmonary bypass, and after administration of protam ine. Data were plotted and interpreted according to the method of Blan d and Altman: First, a difference less than 1.4 U/ml (i.e., +/-0.7 U/m l) was chosen as acceptable, because it would not cause major difficul ties in clinical interpretation, because it would not cause major diff iculties in clinical interpretation; second, the difference between th e two measurement techniques was plotted against the mean of the two m easures. Results: The mean difference (bias) between heparin concentra tions derived by the Hepcon/HMS device and those obtained by laborator y determination was as expected for measures performed on whole blood versus plasma (1.45 U/ml). Nevertheless, heparin concentrations derive d by the Hepcon/HMS device may be as much as 2.76 U/ml above or 6.17 U /ml below the concentrations measured in the laboratory, differences w ell outside the predetermined limits of agreement and clearly unaccept able for clinical purposes. Conclusion: We conclude that heparin conce ntrations determined with the Hepcon/HMS instrument do not agree with laboratory determination of heparin concentration. Monitoring of hepar in concentrations during bypass with the Hepcon/HMS device cannot be r ecommended.