Monitoring of treatment with vitamin K antagonists: recombinant thromboplastins are more sensitive to factor VII than tissue-extract thromboplastins

Reliability of International Normalized Ratio Results in the CoaguChek Pro II System in a Clinical Setting

The National Institute of Cardiology has previously used the CoaguChek® XS Plus system (Roche Diagnostics International Ltd), comparing capillary blood prothrombin time/international normalized ratio (PT/INR) results with those obtained using BCS-XP/Thromborel (Siemens). We assessed the reliability of PT/INR results using the third-generation CoaguChek Pro II system, the CoaguChek XS Plus system, and cobas® t 411 for citrated plasma analysis. Venous and capillary PT/INR were measured (N = 204). Spearman's correlation, Bland-Altman, and concordance analysis between methods were conducted. Spearman's correlation coefficients between venous/capillary INR were high for CoaguChek Pro II versus CoaguChek XS Plus (r = 0.994), CoaguChek Pro II versus cobas t 411 (r = 0.967), and CoaguChek XS Plus versus cobas t 411 (r = 0.968). Good concordance was observed among capillary methods (concordance coefficient [κ] = 0.888) and remaining relationships (P < .001 for all): cobas t 411 versus CoaguChek XS Plus (κ = 0.696) and cobas t 411 versus CoaguChek Pro II (κ = 0.684). In conclusion, good agreement was observed between CoaguChek Pro II, CoaguChek XS Plus, and cobas t 411.

Standardization of Coagulation Factor V Reference Intervals, Prothrombin Time, and Activated Partial Thromboplastin Time in Mice for Use in Factor V Deficiency Pathological Models

Factor V together with activated factor X forms the prothrombinase complex, which transforms prothrombin into thrombin. The Mus musculus species is characterized by very high levels of this factor and short clotting times, which hinders accurate measurements. For that reason, a detailed characterization of such parameters is indispensable. A method was designed as part of this study to provide an accurate determination and standardization of factor V levels, prothrombin time and activated partial thromboplastin time in Mus musculus. Those parameters were evaluated in a sample of 66 healthy animals using a semi-automated coagulometer and human diagnostic reagents in an attempt to determine the most appropriate time of day for the extractions. A mouse-based protocol was designed, capable of making corrections to the samples at dilutions of 1:100 for factor V and at of 1:3 for prothrombin time. The goal was to smoothen the calibration curves, which often present with steep slopes and narrow measurement ranges between one calibration point and another. It was found that the most stable period for blood sample extraction was that comprised between the first 6 h of light. No clinical differences were observed between the sexes and reference intervals were established for factor V (95.80% ± 18.14; 25.21 s ± 1.34), prothrombin time (104.31% ± 14.52; 16.85 s ± 1.32) and activated partial thromboplastin time (32.86 s ± 3.01). The results obtained are applicable to human or veterinary biomedical research, to transfusional medicine or to pathological models for diseases such as factor V deficiency.

A retrospective analysis of discordances between international normalized ratio (INR) self-testing and INR laboratory testing in a pediatric patient population

INTRODUCTION

The lack of quality control procedures for home point-of-care (POC) international normalized ratio (INR) devices is a concern. Concomitant laboratory and POC INR testing may be proposed to overcome the lack of quality control. However, a difference between the POC INR and the laboratory INR is not necessarily due to failure of the POC device. This study aimed to identify variables associated with a significant deviation between the POC INR and the laboratory INR.

METHODS

Children included in this retrospective cohort study performed at least one concomitant laboratory and POC INRs. Clinical and laboratory variables were assessed for an association with significant deviation within pairs of INR.

RESULTS

A significant deviation was noted for 30 (15.3%) of the 196 pairs of INR measurements from 124 children. Relative to patients without deviations, patients with deviations were younger (odds ratio =0.91; P = .020), less experienced in the use of POC INR devices (odds ratio =0.89; P = .098), and more likely to have received an INR result from a laboratory using animal thromboplastin (odds ratio =2.81 vs. 0.37 for laboratories using human thromboplastin; P = .016). In a multivariate analysis, younger age and the laboratory's use of animal thromboplastin were associated with significant deviations.

CONCLUSIONS

Although most children had coherent pairs of INR values, the occurrence of deviations raises the question of the origin of the thromboplastin used in the laboratory and emphasizes the need to provide specific quality control procedures for POC INR devices.

Evaluation of STA-NeoPTimal, an extraction thromboplastin reagent with ISI close to 1

INTRODUCTION

The prothrombin time (PT) is the most requested test to investigate patients with congenital or acquired coagulopathies or to monitor oral anticoagulant therapy. However, thromboplastins can show markedly different responsiveness to the defects induced by vitamin K antagonist (VKA) therapy and are thus characterized by their ISI (International Sensitivity Index). INR results are optimal for patients under VKA but for patients screened for other reasons expressing PT results as ratio can be more appropriate. As it is very difficult to define the PT results reporting unit from the PT testing request, it would be ideal to use a thromboplastin with ISI = 1. The study aims to compare our reference PT reagent with two candidate thromboplastins with ISI close to 1.

METHODS

We compared 3 different thromplastins: two rabbit brain extracted based reagents (STA-Neoplastine CI Plus, with ISI = 1.26, routinely used in our laboratory and STA-NeoPTimal with ISI = 1.01) and a recombinant thromboplastin (STA-Neoplastine R with ISI = 0.97). The comparison was done on 175 samples: 75 from individuals without coagulation defects and 100 from patients under VKA.

RESULTS

STA-NeoPTimal and STA-Neoplastine R well correlate to our reference, STA-Neoplastine CI Plus: regression equations are y = 1.186x-0.1351, r²  = .9454 and y = 1.1432x-0.1554, r²  = .9951, respectively. The lowest bias on INR results was obtained with STA-NeoPTimal reagent (interval: -0.7/+0.4).

CONCLUSION

We conclude that STA-NeoPTimal can be used in the laboratory as it gives results comparable to those obtained with STA-Neoplastine CI Plus. Besides, thanks to its ISI = 1, it guarantees reporting a PT ratio equal to INR which avoids errors.