Comparison of three prothrombin time and activated partial thromboplastin time reagent systems on the MLA 700...

To determine the difference in prothrombin time (PT) and activated partial thromboplastin time (aPTT) results among three reagent systems using a single analyzer instrument.

Convenience sample of 100 patient specimens tested in duplicate with three reagent systems: Baxter-Dade, Pacific Hemostasis, and Organon Teknika.

A tertiary hospital that services other institutions within a three-state area.

Patients were divided into four groups: (1) normal preoperative patients who received no anticoagulants, (2) patients who received warfarin for at least the week immediately before the study, (3) patients who received heparin on the day of the testing, and (4) patients with severe liver disease accompanied by abnormal liver function tests.

Coefficients of correlation of Baxter-Dade results versus the other two systems.

PT values were significantly different in normal samples and in warfarin-treated patients. aPTT values were significantly different for normal patients and, for the Organon system only, for heparin-treated patients. When expressed as international normalized ratio (INR) values, taking reagent sensitivity into consideration, the results correlated well. Problems with precipitation when using Organon's system limited its practical utility.

Compatibility between a reagent system and analyzer instrument should be verified by the manufacturer of the instrument. Use of the INR format produced more accurate and comparable results, allowing safer and more effective dosage adjustments. Laboratories should convert PT and aPTT results to the INR format routinely.