Assessment of International Normalized Ratio Using CoaguChek XS and CoaguChek S as Compared With Central Laboratory Testing

Level of agreement between laboratory and point-of-care prothrombin time in patients after stopping or continuation of acenocoumarol anticoagulation: A comparison of diagnostic accuracy

BACKGROUND

Procedures requiring optimisation of the coagulation status of patients using vitamin K antagonists are frequently postponed due to the late availability of laboratory international normalised ratio (INR) test results. A point-of-care (POC) alternative may facilitate early decision-making in peri-operative patients.

OBJECTIVES

To assess the level of agreement between the POC-INR and the laboratory INR in patients who continue or stop vitamin K antagonists to determine whether the POC test may be a good alternative to the laboratory INR.

DESIGN

Study of diagnostic accuracy.

SETTING

Single-centre study at Zaans Medical Centre, The Netherlands.

PATIENTS

Included patients were scheduled for cardioversion (these continued taking vitamin K antagonists), or a surgical procedure (these stopped taking vitamin K antagonists).

MAIN OUTCOME MEASURES

The level of agreement and clinical acceptability of the laboratory and POC-INR results, evaluated by Bland-Altman analysis and error grid analysis.

RESULTS

The surgical and cardioversion groups consisted of 47 and 46 patients, respectively. The bias in the INR in the surgical group was -0.12 ± 0.09 with limits of agreement of -0.29 to 0.05, whereas the cardioversion group showed a bias in the INR of -0.22 ± 0.36 with limits of agreement from -0.93 to 0.48. The percentage errors between methods in the surgical and cardioversion groups were 16 and 21%, respectively. Error grid analysis showed that the diagnostic accuracy of the POC prothrombin time is clinically acceptable as the difference did not lead to a different clinical decision in the surgical group with INR values less than 1.8.

CONCLUSION

The current study shows a good level of agreement and clinical accuracy between the laboratory and POC-INR in patients who stopped anticoagulation intake for surgery. However, in patients who continued their anticoagulation therapy, the agreement between the two methods was less accurate.

Clinical Validation of R-T Estimation for CoaguChek XS INR Results

BACKGROUND

Despite the emergence of several new oral anticoagulants, warfarin remains a widely used form of anticoagulation that continues to have a role in the treatment of cardiac and thrombotic conditions.

OBJECTIVE

The goal of this study was to evaluate whether the R-T estimation, an equation developed in a previous study, was a valid clinical tool in managing patients' warfarin therapy in an anticoagulation clinic in lieu of obtaining a venipuncture international normalized ratio (INR) secondary to a high CoaguChek XS (CXS) INR.

METHODS

This study used a randomized double-blind method to compare the clinical decisions made using venipuncture or CXS machine and recorded the INR, percentage dose change, time to clinical decision from check-in, and scheduled follow-up.

RESULTS

In the analysis of the difference in percentage dose change, a 1.0% (95% CI = -0.78 to 2.68; P = 0.27) difference was observed overall, and a 1.2% (95% CI = -0.59 to 2.95; P = 0.18) difference was observed in the 4 to 5.9 subgroup. Clinical decisions were reached 17 minutes faster (95% CI = 11-24; P < 0.001) overall and 17 minutes faster (95% CI = 10-24; P < 0.001) in the 4 to 5.9 subgroup. Scheduled follow-up was 0.38 weeks sooner (95% CI = 0.01-0.67; P = 0.014) overall and 0.36 weeks sooner (95% CI = 0-0.66; P = 0.041) in the 4 to 5.9 subgroup.

CONCLUSIONS

The results of this study support the use of the R-T estimation for correction of INR values obtained using the CXS meter when the INR is in the range of 4 to 5.9. This correction will allow clinics using this device to more efficiently manage patients taking warfarin.

Correction of Point-of-Care INR Results in Warfarin Patients

BACKGROUND

The measurement of international normalization ratio (INR) may be done by venous blood draw and use of a standard lab, or by fingerstick, using a point of care (POC) device such as the CoaguChek XS® (Roche Diagnostics), and the CoaguChek XS® has been validated to meet the International Organization for Standardization (ISO) performance requirements.

OVERVIEW

The goal of this study was to determine a correction factor for Coaguchek XS INR levels to a predicted venipuncture (VP) INR level.

METHODS

At the end of an anticoagulation clinic visit when a patient had an INR greater than or equal to 4, two INR results existed, that from the Coaguchek XS® meter and a venipuncture INR from the lab. The data were then discreetly recorded as a quality control for our clinic. The data were analyzed for possible significant trends between the two types of INR results.

RESULTS

The equation that was determined to be the best fit to the data was 0.621 × POC + 0.639 = estimated VP. The overall root mean square error (MSE) for the calculated correction was a 0.44 INR. The root mean square errors were 0.41 and 0.58 for the 4 to 5.9 and 6 to 7.9 POC INR groups, respectively.

CONCLUSION

The calculation that was derived in this study is not a surrogate for venipuncture INR in this clinic. However, the estimation of the INR may be useful clinically in guiding decision making in the future. (INR, Point of Care, Anticoagulation, Hematology).