Correlation between activated clotting time and activated partial thromboplastin times.
OBJECTIVE
To evaluate the correlation between clotting time tests and heparin concentration, the correlation between activated clotting time (ACT) and activated partial thromboplastin time (aPTT) results, and to compare the clinical decisions based on ACT results with those based on aPTT results.


METHODS
Retrospective evaluation of a large database containing heparin concentrations, ACT results (1 device), and aPTT results (3 different instruments: 2 bedside, 1 laboratory-based). Correlations between heparin concentrations and clotting time tests and between ACT results and aPTT results were determined. Clinical decisions regarding heparin dosage adjustments based on ACT results were compared with those based on aPTT results.


RESULTS
Correlations between clotting time tests and heparin concentrations were r = 0.72 for ACT and r = 0.74-0.86 for the aPTT instruments. The laboratory-based aPTT had the highest correlation to heparin concentrations. The correlation between ACT and aPTT results ranged from r = 0.64-0.67. Heparin dosage adjustment decisions based on ACT results agreed with decisions based on aPTT results 59-63% of the time.


CONCLUSIONS
The laboratory-based aPTT has a stronger correlation to heparin concentration than the bedside-based aPTT and ACT. The correlation between ACT and aPTT was similar among 3 different aPTT instruments. Decisions to adjust heparin therapy based on ACT results differed from decisions based on aPTT results more than one-third of the time.
Smythe
Maureen A
MA
Department of Pharmaceutical Services, William Beaumont Hospital, 3601 W. 13 Mile Rd., Royal Oak, MI 48073-6769, USA. msmythe@beaumont.edu
Koerber
John M
JM
Nowak
Sandra N
SN
Mattson
Joan C
JC
Begle
Robert L
RL
Westley
Susan J
SJ
Balasubramaniam
Mamtha
M
D000925:Anticoagulants / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology*; D016208:Databases, Factual; D004305:Dose-Response Relationship, Drug; D006493:Heparin / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology*; D006801:Humans; D010314:Partial Thromboplastin Time; D012189:Retrospective Studies; D014914:Whole Blood Coagulation Time
D000925:Anticoagulants; D006493:Heparin