Two instruments to determine activated partial thromboplastin time: implications for heparin monitoring.
OBJECTIVE
To measure the difference in therapeutic ranges of activated partial thromboplastin time (APTT) between two laboratory devices.


METHODS
Prospective, controlled laboratory study.


METHODS
University-affiliated hospital.


METHODS
Thirty inpatients receiving intravenous unfractionated heparin for treatment of myocardial infarction, unstable angina, deep venous thrombosis, or pulmonary embolism.


METHODS
Therapeutic APTT ranges were determined by a portable (whole blood assay) and a central laboratory device (plasma assay) based on heparin serum concentrations. They were compared with APTT ranges equivalent to 1.5-2.5 times the mean normal determination.


RESULTS
The central laboratory and portable devices produced therapeutic ranges of 61-93 and 56-73 seconds, respectively. Both differed from conventional therapeutic ratios of 1.5-2.5 times the mean normal (41-68 sec). Mean absolute APTT differences between instruments were statistically significant (12 +/- 20 sec, p<0.006), and 58% of paired APTT values differed by more than 10 seconds.


CONCLUSIONS
A fixed APTT ratio as a goal for monitoring unfractionated heparin may result in significant underanticoagulation. Individual therapeutic APTT ranges must be reported for each instrument if more than one is used for heparin monitoring.
Taylor
C T
CT
Department of Pharmacy Practice, Auburn University School of Pharmacy, Alabama, USA.
Petros
W P
WP
Ortel
T L
TL
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000789:Angina, Unstable / Q000097:blood / Q000188:drug therapy; D000925:Anticoagulants / Q000097:blood* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D006493:Heparin / Q000097:blood* / Q000627:therapeutic use; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000097:blood / Q000188:drug therapy; D010314:Partial Thromboplastin Time; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000097:blood / Q000188:drug therapy; D020246:Venous Thrombosis / Q000097:blood / Q000188:drug therapy
D000925:Anticoagulants; D006493:Heparin