Measurement of the activated clotting time during cardiopulmonary bypass: differences between Hemotec ACT and Hemochron Jr apparatus.
BACKGROUND
Measurement of the activated clotting time (ACT) represents a standard method for coagulatory assessments. The test employs specific agents to trigger the coagulation process. The present study aimed to compare kaolin (Hemotec) versus a combination of silica, kaolin and phospholipid (Hemochron Jr) ACTs.


METHODS
Hemotec and Hemochron Jr ACT monitors were compared by simultaneous measurement of paired arterial blood samples (n = 114) with respect to precision and bias during clinical conditions of cardiopulmonary bypass (CPB). The influence of haemodilution on the ACT was tested in an ex-vivo model.


RESULTS
The precision of Hemotec and Hemochron Jr ACT measurements attained 21 +/- 2.6 s versus 27.0 +/- 2.6 s (p = 0.126) during CPB and 2.5 +/- 2.2 s versus 9.4 +/- 6.9 s (p = 0.000) after protamine administration, respectively. The Hemochron Jr monitor was associated with a bias of -102 +/- 13.7 s compared to the Hemotec ACT monitor (p = 0.000) during CPB and -6.9 +/- 2.9 s after protamine (p = 0.025). Linear regression analysis of ACT readings between monitors reached r = 0.526 (p = 0.000). Hemochron Jr ACT values correlated with the erythrocyte volume fraction r = 0.379 (p = 0.000). Ex-vivo data indicated that the Hemotec ACT monitor was associated with relatively higher ACT readings after haemodilution.


CONCLUSIONS
The ACT is not a standardized measure. Test results are strongly associated with the specific compounds used to initiate the coagulation process.
Svenmarker
S
S
Department of Surgical and Perioperative Science, University Hospital of Umeå, Umeå, Sweden. staffan.svenmarker.us@vll.se
Appelblad
M
M
Jansson
E
E
Häggmark
S
S
D000368:Aged; D015982:Bias; D002315:Cardiopulmonary Bypass; D005260:Female; D006438:Hemodilution; D006801:Humans; D007202:Indicators and Reagents; D007616:Kaolin; D008297:Male; D010743:Phospholipids; D012015:Reference Standards; D012822:Silicon Dioxide; D014914:Whole Blood Coagulation Time / Q000295:instrumentation* / Q000379:methods / Q000592:standards
D007202:Indicators and Reagents; D010743:Phospholipids; D007616:Kaolin; D012822:Silicon Dioxide