Clinically significant differences between point-of-care analysers and a standard analyser for monitoring the International Normalized Ratio in oral anticoagulant therapy: a multi-instrument evaluation in a hospital outpatient setting

Correction factor to improve agreement between point-of-care and laboratory International Normalized Ratio values

PURPOSE

Results of a research project to quantify and improve the accuracy of point-of-care (POC) International Normalized Ratio (INR) values are reported.

METHODS

The accuracy of POC INR values relative to laboratory-measured INR values was retrospectively assessed in a cohort of patients with same-day INR determinations by both methods. Univariate linear regression was performed to derive a correction factor for POC INR values of >3; this correction factor was validated in a second cohort.

RESULTS

In the derivation cohort (259 patients and 344 paired INR results), agreement of POC values with corresponding laboratory INR values at two specified thresholds (±15% and ±25%) was 51.2% and 66.6%, respectively; for POC INR values of >3 (n = 205), agreement was lower (24.9% and 44.9%, respectively). Univariate linear regression yielded a coefficient of 0.77 (95% confidence interval, 0.76-0.79; p < 0.001). Applying a correction factor of 0.8 to POC INR values in a validation cohort (169 patients and 209 paired INR values) significantly improved the accuracy of POC INR values of >3 relative to laboratory values (from 7% to 71.1% at the lower threshold and from 23.5% to 88.8% at the higher threshold, p < 0.0001 for both comparisons).

CONCLUSION

Agreement between POC and laboratory INR results in one institution was poor, especially when POC INR values exceeded 3. Application of an institution-specific correction factor to POC INR values of >3 improved agreement with laboratory INR results but would not have significantly reduced differences in protocol-based warfarin dosage adjustments.

Comparison of the INR Values Measured by CoaguChek XS Coagulometer and Conventional Laboratory Methods in Patients on VKA Therapy

BACKGROUND

Warfarin, which is a widely used oral anticoagulant, has a narrow therapeutic window and requires regular international normalized ratio (INR) monitoring to maintain optimal anticoagulation. Recently, several portable coagulometers have been developed to measure INR levels.

OBJECTIVE

To compare the INR results obtained by a portable coagulometer (CoaguChek XS) and a standard laboratory method (STAGO STA-R).

METHODS

Overall, 433 consecutive patients (male: 191, median age: 61 [44-86] years) who were admitted to outpatient anticoagulation clinic were enrolled in this study. Each patient was tested for INR using portable CoaguChek XS and STAGO STA-R automatic laboratory coagulometer. Correlation between methods was assessed using the Pearson correlation test and Cohen κ test. Bland-Altman plot was used to identify mean difference and 95% limits of agreement.

RESULTS

The mean INR values for CoaguChek XS and STAGO STA-R were 2.54 ± 1.17 and 2.79 ± 1.39, respectively. There was a strong positive correlation between the 2 methods ( r = .966; 95% confidence interval [CI]: 0.95-0.97, P < .001). The Bland-Altman analysis gave a mean difference of 0.26 ± 0.40 between the 2 methods, with a 95% limit of agreement of -0.54 to 1.05. In patients with INR values >5.0, there was only a moderate correlation ( r = .676; 95% CI: 0.38-0.89, P = .002), and the mean difference of INR tended to increase as mean INR values increased. There was a high overall agreement between the 2 methods (κ = .751; 95% CI: 0.69-0.80; P < .001).

CONCLUSION

There was good consistency between traditional laboratory testing and CoaguChek XS coagulometer, which provides rapid and reliable INR analysis.

Reliability of a point-of-care device for international normalized ratio testing during the three surgical phases of orthotopic liver transplantation: a retrospective observational study

PURPOSE

To investigate the reliability of a point-of-care device, the HEMOCHRON(®) Jr. Signature, for measuring the international normalized ratio (INR) during the three surgical phases of liver transplantation.

METHODS

A retrospective review was performed on patients undergoing liver transplantation during July to December 2013. Thirty-one patients who had simultaneous laboratory and point-of-care INR readings from each phase of liver transplant surgery (paleohepatic, anhepatic, and neohepatic) were eligible for inclusion. Bland-Altman analysis, Spearman's rank correlation, and four quadrant plots were used to compare INR results from the point-of-care device (pocINR) with those from the laboratory (labINR).

RESULTS

Based on the Bland-Altman analysis, mean biases (95% prediction interval) were 0.10 (0.03 to 0.17), 0.19 (0.12 to 0.27), and 0.21 (0.01 to 0.43) for the paleohepatic, anhepatic, and neohepatic phases, respectively. The pocINR device showed a systematic underestimation of the labINR. The Spearman's rank correlation coefficients (95% confidence interval [CI]) were: Ρ = 0.90 (95% CI 0.80 to 0.95); Ρ = 0.92 (95% CI 0.71 to 0.93); and Ρ = 0.71 (95% CI 0.46 to 0.85), respectively. Direction-of-change analysis between the paleohepatic to anhepatic and the anhepatic to neohepatic phases showed strong concordance of 84% and, also considering the small bias between the measurements, supports the use of the pocINR device in the clinical management of liver transplant surgery.

CONCLUSION

Point-of-care INR was accurate prior to hepatic reperfusion, but reliability decreased in the neohepatic phase.

Limits of agreement between measures obtained from standard laboratory and the point-of-care device Hemochron Signature Elite(R) during acute haemorrhage

BACKGROUND

Rapid diagnosis of coagulopathy in the bleeding patient using point-of-care (POC) devices would be ideal. The Hemochron Signature Elite(®) (HC(®)) is a POC device that determines international normalized ratio (INR) and activated partial thromboplastin time (aPTT). The aim of the study was to evaluate the agreement for INR and aPTT between the HC(®) and standard laboratory values in acute haemorrhage.

METHODS

This was a single-centre observational prospective study including patients with acute haemorrhage. Laboratory INR and aPTT were compared with simultaneous measurements performed with the HC(®). The diagnostic performance of HC(®) was determined; bias and limits of agreement were calculated according to the method of Bland and Altman.

RESULTS

Seventy-two pairs of measurements from 39 patients were analysed. The bias between the INR-HC(®) and aPTT-HC(®) measurements and the central laboratory were 0.02 and -1.13, respectively. The Spearman's correlation coefficients for the INR-HC(®)/INR-lab and the aPTT-HC(®)/aPTT-lab were 0.68 and -0.29, respectively. Twenty-seven per cent of INR-HC(®) values and 89% of the aPTT-HC(®) values exceeded the predefined limits of agreement. The INR-HC(®) measurement identified patients with a central laboratory INR >1.5 with a sensitivity, specificity, and positive and negative predictive values of 83%, 70%, 76%, and 77%, respectively.

CONCLUSIONS

The results showed a lack of agreement between the INR-HC(®) and the aPTT-HC(®) measurements and the standard laboratory in the context of acute haemorrhage. The INR-HC(®) showed moderate performance as a decision-making tool to detect coagulopathy in the context of acute haemorrhage.

Transiently increased variation between a Point-of-Care and laboratory INR method after a long period of correlation: a case study demonstrating the need for ongoing correlation of POC with the central laboratory

OBJECTIVES

To perform long-term comparison between laboratory Stago and Point-of-Care (POC) i-STAT methods for determining the international normalized ratio (INR).

METHODS

This was a multicenter method comparison of patient INR results and factors related to performance variance.

RESULTS

For 5 years, the assays demonstrated close patient correlation within and above the 3.5 INR therapeutic range cutoff (bias, 0.23 INR units). Patient results above 3.5 INR were bimodal, with 60% demonstrating an i-STAT INR bias of less than 0.5. Several patient conditions were associated with the presence of a higher i-STAT bias. In year 6, a broader range i-STAT bias developed, increasing to 0.73 INR units. The increased bias persisted for 3 years, then returned to initial levels following i-STAT adjustments. The substantial increase in i-STAT bias after a long period of stability was partly corrected by renewed correlation to the international reference preparation. Additional assay drift is discussed in relation to thromboplastin reagents and other testing variables.

CONCLUSIONS

This study emphasizes the need for continual laboratory correlation with POC devices and caution in using published comparisons.

Comparison of international normalized ratio measurement between CoaguChek XS Plus and STA-R coagulation analyzers

Background. Point-of-care testing (POCT) coagulometers are increasingly being used in the hospital setting. We investigated whether the prothrombin time international normalized ratio (INR) results by CoaguChek XS Plus (Roche Diagnostics GmbH, Mannheim, Germany) can be used reliably without being confirmed with the INR results by STA-R system (Diagnostica Stago S.A.S, Asnières sur Seine, France). Methods. A total of 118 INR measurements by CoaguChek XS Plus and STA-R were compared using Passing/Bablok regression analysis and Bland-Altman plot. Agreement of the INR measurements was further assessed in relation to dosing decision. Results. The correlation of INR measurements between CoaguChek XS Plus and STA-R was excellent (correlation coefficient = 0.964). The mean difference tended to increase as INR results increased and was 0.25 INR in the therapeutic range (2.0-3.0 INR). The overall agreement was fair to good (kappa = 0.679), and 21/118 (17.8%) INR measurements showed a difference in dosing decision. Conclusion. The positive bias of CoaguChek XS Plus may be obvious even in the therapeutic INR range, and dosing decision based on the CoaguChek XS Plus INR results would be different from that based on the STA-R results. The INR measurements by POCT coagulometers still need to be confirmed with the laboratory INR measurements.

Evaluation of Thrombi-Stat MC1 for whole blood and plasma international normalized ratio in comparison with a laboratory method

INTRODUCTION

The precision and comparability of the international normalized ratio (INR) analyzed by the Thrombi-Stat MC1 coagulation testing system were evaluated before using as a point-of-care testing.

METHODS

Three levels of control materials were used for within-run and between-run precision study. Comparison study of INR determination from citrated whole blood (INR-WB) and citrated plasma (INR-PL) analyzed by the Thrombi-Stat MC1 with those by the validated method, Sysmex® CS-2100i (INR-CS), was performed.

RESULTS

The within-run coefficient of variations (CVs) of INR by the Thrombi-Stat MC1 were 3.60% to 4.80%. For between-run precision, the CVs were 4.26 to 4.93%. Fifty-four plasmas from patients receiving warfarin were included for comparability testing. There were good correlation and agreement between both INR-WB and INR-PL compared with INR-CS. Eighty-seven percent of INR-WB and 100% of INR-PL were within ± 0.5 units of the INR-CS. Given that the therapeutic range was INR-CS of 2-3, 3.7% of INR-WB and 5.56% of INR-PL were discordant with the INR-CS.

CONCLUSION

The precision and comparability to validated method of the Thrombi-Stat MC1 were acceptable. Either citrated whole blood or plasma may be used as samples in this system. Impact on the management of patients must be taken into consideration prior to the implementation of this system.

Utility of a point-of-care device for rapid determination of prothrombin time in trauma patients: a preliminary study

BACKGROUND

Rapid and accurate determination of prothrombin time in trauma patients may help to faster control of bleeding induced coagulopathy. The goal of this prospective observational study was to investigate the accuracy of bedside measurements of prothrombin time by the mean of a point-of-care device (INRatio) in trauma patients.

METHODS

Fifty blood samples were drawn at admission and during the acute care phase for standard coagulation assays (prothrombin time, International Normalized Ratio [INR], and fibrinogen) and INRatio testing (INR(A)) from 48 trauma patients.

RESULTS

Standard coagulation assays were available after a mean of 66 minutes. Median Injury Severity Score was 18, and 16 patients (33%) had a coagulopathy. Significant correlation was found between INR and INR(A) (r: 0.93, 95% confidence interval: 0.87-0.96). The mean difference (bias) for INR was 0.00, and standard deviation (precision) of the difference was 0.78. However, in cases where there was decreased hemoglobin (<10 gr · L(-1)) and fibrinogen (<1.5 gr · L(-1)), bias and precision were increased. To predict the need for fresh frozen plasma transfusion (INR > 1.5), INR(A) cutoff value of 1.3 resulted in a sensitivity of 92% and a specificity of 79%. The area under the receiver operating characteristic curve was 0.946 (95% confidence interval: 0,845-0,982).

CONCLUSION

INRatio may be a useful device in the management of trauma patients with ongoing or suspected coagulopathy that may help to save at least 60 minutes in the process of obtaining a prothrombin time result. It may allow earlier detection of coagulopathy and, together with vital sign and hemoglobin, may help to guide fresh frozen plasma transfusion.

Comparison of point-of-care testing (POCT): i-STAT(®) international normalized ratio (INR) vs reference laboratory INR in pediatric patients undergoing major surgery

BACKGROUND

The aim of the study was to compare international normalized ratio (INR) results obtained by point-of-care testing (i-STAT® device) with the reference laboratory INR in children undergoing major surgery with expected significant blood loss.

METHODS

  Pediatric patients undergoing craniofacial, spine, hip, or cancer surgery were included. Blood samples for coagulation testing were tested at several intraoperative time points and generally withdrawn from the arterial catheter, if accessible. A volume of 1.4 ml citrated blood was used for the reference laboratory INR test, and 0.1 ml of blood was taken for the whole blood INR test using the i-STAT® device. Blood samples for both tests were withdrawn at the same time and immediately analyzed with both devices.

RESULTS

A total of 169 paired blood samples were taken intraoperatively from 44 pediatric patients [IQR 0.9-10.7 years (median 3.3)]. Reference laboratory INR ranged from 0.96 to 3.43 (mean 1.40; sd 0.32) and INR of i-STAT® from 0.95 to 2.29 (mean 1.26; sd 0.22). The correlation coefficient was 0.83 (P < 0.001), and the bias values were 0.12 and 0.55 at the medical decision level of ≤2.0 and >2.0, respectively.

CONCLUSIONS

In the perioperative setting, point-of-care INR testing in children using the i-STAT® device is a reliable and easy-to-handle method for INR values ≤2.0, while INR values >2.0 might be underestimated.

Use of error grid analysis to evaluate acceptability of a point of care prothrombin time meter

BACKGROUND

Statistical methods (linear regression, correlation analysis, etc.) are frequently employed in comparing methods in the central laboratory (CL). Assessing acceptability of point of care testing (POCT) equipment, however, is more difficult because statistically significant biases may not have an impact on clinical care. We showed how error grid (EG) analysis can be used to evaluate POCT PT INR with the CL.

MATERIALS AND METHODS

We compared results from 103 patients seen in an anti-coagulation clinic that were on Coumadin maintenance therapy using fingerstick samples for POCT (Roche CoaguChek XS and S) and citrated venous blood samples for CL (Stago STAR). To compare clinical acceptability of results we developed an EG with zones A, B, C and D.

RESULTS

Using 2nd order polynomial equation analysis, POCT results highly correlate with the CL for CoaguChek XS (R(2)=0. 955) and CoaguChek S (R(2)=0. 93), respectively but does not indicate if POCT results are clinically interchangeable with the CL. Using EG it is readily apparent which levels can be considered clinically identical to the CL despite analytical bias.

CONCLUSION

We have demonstrated the usefulness of EG in determining acceptability of POCT PT INR testing and how it can be used to determine cut-offs where differences in POCT results may impact clinical care.

Monitoring of haemostasis in liver transplantation: comparison of laboratory based and point of care tests

During orthotopic liver transplanatation haemostasis is often disturbed and coagulation monitoring is mandatory. We compared the results obtained by whole blood prothrombin time and activated partial thromboplastin time assays (Hemochron) and thrombelastometry (ROTEM) 05) with laboratory coagulation assays (prothrombin time, activated partial prothrombin time, fibrinogen, and platelet count) in samples obtained during orthotopic liver transplantations. Determination of prothrombin time and activated partial prothrombin time using the Hemochron device showed good correlation with laboratory coagulation assays (r = 0.912, p < 0.001, and r = 0.794, p < 0.001). Maximum clot firmness as determined by thrombelastometry correlated well with platelet count (r = 0.779, p < 0.001) and, to a lesser degree, with fibrinogen concentration (r = 0.590, p < 0.001). During orthotopic liver transplantation, prothrombin time and activated partial prothrombin time can be reliably determined by the Hemochron device, while thrombelastometry allows assessment of platelet count and fibrinogen concentration.

Point-of-care international normalized ratio testing accelerates thrombolysis in patients with acute ischemic stroke using oral anticoagulants

BACKGROUND AND PURPOSE

Thrombolysis in patients using oral anticoagulants (OAC) and in patients for whom information on OAC status is not available is frequently delayed because the standard coagulation analysis procedure in central laboratories (CL) is time-consuming. By using point-of-care (POC) coagumeters, international normalized ratio (INR) values can be measured immediately at the bedside. The accuracy and effectiveness of POC devices for emergency management in acute ischemic stroke has not been tested.

METHODS

In phase 1, the reliability of emergency INR POC measurements in comparison to CL was determined. In phase 2, patients with ischemic stroke admitted within the time frame for systemic thrombolysis and who were either using OAC or for whom information on OAC status was not available were enrolled. Patients received thrombolysis if POC INR was <or=1.5. Precision and time gain was recorded for INR as measured by POC vs CL.

RESULTS

In phase 1 (n=113), Bland-Altman analysis showed close agreement between POC and CL, and Pearson correlation was highly significant (r=0.98; P<0.01). In phase 2, 48 patients were included, of whom 70.8% were using OAC; 23 patients received thrombolysis. After subtracting the time needed for the diagnostic work-up, the net time gain was 28+/-12 minutes (mean+/-SD).

CONCLUSIONS

Measuring INR by POC in an emergency setting is sufficiently precise in OAC acute stroke patients and substantially reduces the time interval until INR values are available and therefore may hasten the initiation of thrombolysis.