| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Oak Ridge Poster Sessions |
a author for correspondence: fax 916-734-3320, e-mail bgosselli{at}clb.ucdmc ucdavis.edu
Utilization of point-of-care (POC) devices for monitoring patients receiving oral anticoagulant therapy is increasing. In this study, we compared three different POC devices with the clinical laboratory method of determining prothrombin times (PT) and the associated International Normalized Ratio (INR).
After approval by our Institutional Review Board, we obtained consent from and enrolled 40 consecutive patients. All patients had documented stabilization of their INR, and patients who had been taking coumadin <7 days were excluded. Whole-blood fingerstick samples were acquired by a single nurse practitioner (R.H.) and tested on the Coumatrak PT monitor (Boehringer Mannheim). Samples were then drawn from the patients by antecubital phlebotomy with a 20-gauge butterfly needle and syringe. The peripherally drawn whole blood was immediately (within 15 s of phlebotomy) tested on the Coumatrak and CoaguChek Plus (Boehringer Mannheim) monitors. The residual blood was then anticoagulated by placing into 32 g/L sodium citrate-containing tubes (Becton Dickinson), and the citrated whole blood was immediately tested on the Thrombolytic Assessment System (TAS; Cardiovascular Diagnostics). The citrated samples were then centrifuged at 1800g for 15 min, and the plasma obtained was analyzed by the clinical laboratory PT method within 2 h of collection. To avoid cold activation of factor VII, citrated samples were kept at room temperature until assay.
Both Coumatrak and CoaguChek Plus are based on the same method principle, utilizing a test cartridge containing rabbit brain thromboplastin, stabilizers, and preservatives. A single drop of whole blood (noncitrated) is added to the test cartridge inserted into the monitor. The blood travels by capillary action, mixes with thromboplastin in the reagent chamber, and continues to flow along a reaction track until a clot is formed. An optical laser monitors this blood flow, and the resulting time to clot formation is displayed in seconds; PT ratio and INR are also reported.
Each TAS PT-One test cartridge contains lyophilized thromboplastin from human placenta, calcium chloride, and buffers coated with paramagnetic iron oxide particles (PIOP). The citrated blood is added to the single-use test cartridge positioned within the TAS analyzer. A pulsating magnetic field is then initiated, causing the PIOP to move up and down. As the sample clots, the decrease in PIOP motion is detected and the resulting clotting time displayed. Each cartridge lot is magnetically encoded with an International Sensitivity Index (ISI) and a reference mean value, 0.99 and 12.2 s, respectively.
For laboratory determination of PT, we used Innovin (Dade International) thromboplastin, which contains recombinant human tissue factor, calcium chloride, and buffers. All testing was performed on the MLA 1000C coagulation analyzer (Medical Laboratory Automation). The ISI for this method is 0.98, with mean PT of 11.1 s.
Linear regression analysis and bias analysis were performed in terms of the clinical laboratory method serving as the reference. Student's paired t-test was also used to determine whether the differences between POC devices and the parent clinical laboratory method were statistically significant (P <0.05).
The summary of data (Table 1
and Fig. 1
) indicates only marginal agreement of the clinical laboratory
method with the Coumatrak and CoaguChek Plus devices. This is not
unexpected, given the sensitivity differences indicated by the ISI. The
agreement improved slightly when the methods were compared in terms of
INR values, but the differences remained statistically significant.
|
|
For both PT and INR, the TAS method agreed more closely with the
clinical laboratory method than did the other POC devices (Table 1
),
especially for samples with INR <2.5 (Fig. 1
). In theory, using INR
(1) should have minimized the differences between methods
and devices, but we did not find this to be the case here. Indeed, 25%
(10 of 40) of the Coumatrak results and 17.5% (7 of 40) of the
CoaguChek Plus results indicated adequate anticoagulation (INR
2.0–3.0) (2) when subtherapeutic anticoagulation was
reported by the parent clinical laboratory or TAS methods.
From our data we conclude the following: The Coumatrak and CoaguChek Plus methods significantly underestimated the INR. The TAS PT-One is more comparable with the parent laboratory method, both of which use a highly sensitive thromboplastin reagent. Differences between methods were not fully corrected with the INR.
Footnotes
Univ. of California, Davis Med. Ctr., 4625 2nd Ave., Rm. 3203, Sacramento, CA 95817
References
The following articles in journals at HighWire Press have cited this article:
|
|
 |
|
  R. D. McBane II, C. L. Felty, M. L. Hartgers, R. Chaudhry, L. K. Beyer, and P. J. Santrach Importance of Device Evaluation for Point-of-Care Prothrombin Time International Normalized Ratio Testing Programs Mayo Clin. Proc., February 1, 2005; 80(2): 181 - 186. [Abstract] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
