Uncertainty of International Sensitivity Index and International Normalized Ratio

2013 ◽  
Vol 11 (8) ◽  
pp. 1615-1617 ◽  
Author(s):  
A. M. H. P. van den Besselaar ◽  
E. Witteveen ◽  
F. J. M. van der Meer
Keyword(s):  
International Normalized Ratio ◽  
Sensitivity Index ◽  
International Sensitivity Index

Multi-Center Study of Thromboplastin Calibration Precision – Influence of Reagent Species, Composition, and International Sensitivity Index (ISI)

1993 ◽  
Vol 69 (01) ◽  
pp. 035-040 ◽  
Author(s):  
A M H P van den Besselaar ◽  
R M Bertina
Keyword(s):  
Oral Anticoagulants ◽  
International Normalized Ratio ◽  
The Other ◽  
World Health ◽  
Rabbit Brain ◽  
Sensitivity Index ◽  
Bovine Plasma ◽  
Significant Difference ◽  
The Mean ◽  
International Sensitivity Index

SummaryFour thromboplastin reagents were tested by 18 laboratories in Europe, North-America, and Australasia, according to a detailed protocol. One thromboplastin was the International Reference Preparation for ox brain thromboplastin combined with adsorbed bovine plasma (coded OBT/79), and the second was a certified reference material for rabbit brain thromboplastin, plain (coded CRM 149R). The other two thromboplastin reagents were another rabbit plain brain thromboplastin (RP) with a lower ISI than CRM 149R and a rabbit brain thromboplastin combined with adsorbed bovine plasma (RC). Calibration of the latter two reagents was performed according to methods recommended by the World Health Organization (W. H. O.).The purpose of this study was to answer the following questions: 1) Is the calibration of the RC reagent more precise against the bovine/combined (OBT/79) than against the rabbit/plain reagent (CRM 149R)? 2) Is the precision of calibration influenced by the magnitude of the International Sensitivity Index (ISI)?The lowest inter-laboratory variation of ISI was observed in the calibration of the rabbit/plain reagent (RP) against the other rabbit/plain reagent (CRM 149R) (CV 1.6%). The highest interlaboratory variation was obtained in the calibration of rabbit/plain (RP) against bovine/combined (OBT/79) (CV 5.1%). In the calibration of the rabbit/combined (RC) reagent, there was no difference in precision between OBT/79 (CV 4.3%) and CRM 149R (CV 4.2%). Furthermore, there was no significant difference in the precision of the ISI of RC obtained with CRM 149R (ISI = 1.343) and the rabbit/plain (RP) reagent with ISI = 1.14. In conclusion, the calibration of RC could be performed with similar precision with either OBT/79 or CRM 149R, or RP.The mean ISI values calculated with OBT/79 and CRM 149R were practically identical, indicating that there is no bias in the ISI of these reference preparations and that these reference preparations have been stable since their original calibration studies in 1979 and 1987, respectively.International Normalized Ratio (INR) equivalents were calculated for a lyophilized control plasma derived from patients treated with oral anticoagulants. There were small but significant differences in the mean INR equivalents between the bovine and rabbit thromboplastins. There were no differences in the interlaboratory variation of the INR equivalents, when the four thromboplastins were compared.

In-house Calibration of the International Sensitivity Index or Calibration Curve for Determination of the International Normalized Ratio

2004 ◽  
Vol 128 (3) ◽  
pp. 308-312
Author(s):  
William F. Brien ◽  
Linda Crawford ◽  
Anne Raby ◽  
Harold Richardson
Keyword(s):  
Calibration Curve ◽  
Oral Anticoagulants ◽  
International Normalized Ratio ◽  
Sensitivity Index ◽  
Improve Performance ◽  
Accuracy And Precision ◽  
The Stability ◽  
Method Of Assessment ◽  
International Sensitivity Index

Abstract Context.—The international normalized ratio (INR) has been used since 1983 to standardize prothrombin time results for patients on oral anticoagulants. However, significant interlaboratory variations have been noted. Attempts have been made to address these differences with the use of instrument-specific International Sensitivity Index (ISI) values and in-house calibration of ISI values. Objective.—To assess the performance of laboratories using a calibration curve for INR testing. Design.—Attempts to improve performance of the INR include the use of instrument-specific ISI values, model-specific ISI values, in-house calibration of ISI values, and more recently, the preparation of a calibration curve. Several studies have shown an improvement in performance using these procedures. In this study of licensed laboratories performing routine coagulation testing in the Province of Ontario, Canada, the determination of the INR by a calibration curve was compared with the laboratories' usual method of assessment. These methods were subsequently analyzed by comparing the results to instrument-specific ISI, model-specific ISI, and in-house calibrators. International normalized ratios derived by both methods were analyzed for accuracy and precision. The stability of a calibration curve was also investigated. Results.—Performance of INR testing has improved with use of a calibration curve or in-house calibrators. Conclusion.—The results confirm that either in-house calibrators or the calibration curve improve performance of INR testing. The calibration curve may be easier to use and appears stable up to 4 months.

Assessment of the Influence of Citrate Concentration on the International Normalized Ratio (INR) Determined with Twelve Reagent-instrument Combinations

1998 ◽  
Vol 80 (08) ◽  
pp. 258-262 ◽  
Author(s):  
Veena Chantarangkul ◽  
Marigrazia Clerici ◽  
Barbara Negri ◽  
Pier Mannuccio Mannucci ◽  
Armando Tripodi
Keyword(s):  
External Quality Assessment ◽  
International Normalized Ratio ◽  
Local System ◽  
Sensitivity Index ◽  
External Quality ◽  
Citrate Concentration ◽  
Coagulation Tests ◽  
Reference Preparation ◽  
Anticoagulated Patients ◽  
International Sensitivity Index

SummaryCitrate concentration is one of the variables that can affect coagulation tests. However, few studies have so far been performed to assess the magnitude of this effect on coagulation tests in general and PT in particular. The aim of this study was to assess the extent of influence of citrate concentration on the PT test with results expressed as INR. Twelve reagent-instrument combinations (systems) were calibrated vs. the Reference Preparation BCT/441 using plasmas collected in either 105 mM or 129 mM citrate from normals and anticoagulated patients (OAT). PTs for plasmas collected in 129 mM citrate were longer than those collected in 105 mM both for normals and patients on OAT, but the ratios (patient-to-normal clotting times) for the two citrate concentrations were significantly different in many instances, implying that the International Sensitivity Index (ISI) is also different. ISIs for calibrations with plasmas collected in 105 mM were greater (up to 10%) than those with plasmas collected in 129 mM citrate. When PT ratios were transformed into INR using crossover ISIs (i.e., plasmas collected in 105 mM and ISI determined with plasmas collected in 129 mM citrate, or vice versa) we found that an INR of 4.5 could be up to 20% apart from the value that would have been obtained if the appropriate ISI was used. Moreover, if the ISI determined with the manual technique was used to convert PTs obtained with a particular instrument into INR, the effect of citrate concentration was even greater (INR difference up to 64%). Should these observations be valid for other systems, they might provide additional explanations for the frequent reports which document discrepancies in the INR determined with different systems to which incorrect ISI might have been applied. World-wide consensus on a single citrate concentration to collect patients’ as well as lyophilized plasmas to be used in External Quality Assessment Schemes and for local system calibration is therefore urgently needed.

Multicenter Evaluation of Lyophilized and Deep-frozen Plasmas for Assignment of the International Normalized Ratio

1999 ◽  
Vol 82 (11) ◽  
pp. 1451-1455 ◽  
Author(s):  
L. L. Houbouyan-Reveillard ◽  
M. F. Aillaud ◽  
K. W. E. Denson ◽  
C. Droullé ◽  
M. Johnston ◽  
...  
Keyword(s):  
Prothrombin Time ◽  
External Quality Assessment ◽  
Calibration Procedure ◽  
International Normalized Ratio ◽  
Sensitivity Index ◽  
Local Calibration ◽  
External Quality ◽  
Different Types ◽  
Time Systems ◽  
International Sensitivity Index

SummaryThe interlaboratory variation of the International Normalized Ratio (INR) in various external quality assessment schemes is still relatively high. This is partly caused by inaccuracy of manufacturers’ stated International Sensitivity Index (ISI) and/or local instrumentation effects. The interlaboratory variation and accuracy of INR determinations may be improved by a local calibration procedure based on lyophilized plasmas with assigned INRs. The purpose of the present study was to determine INR values for different types of lyophilized plasmas to be used for local calibration. A total of 13 lyophilized plasmas (one normal, six from coumarin-treated patients, six artificially depleted) were analyzed by 10 laboratories, each using five calibrated prothrombin time (PT) systems. INRs were calculated for each plasma using each laboratory’s specific ISI and mean normal prothrombin time values. In the same way, five deep-frozen pooled plasmas from coumarin-treated patients were analyzed. There were significant INR differences for the lyophilized plasmas between the prothrombin time systems. The differences were relatively small for the deep-frozen coumarin plasmas (CV 2.6-3.3%) and three lyophilized coumarin plasmas from one manufacturer (CV 3.7-4.8%). Important INR differences were observed for three lyophilized coumarin plasmas from another manufacturer (CV 9.5-14.1%) and several artificially depleted plasmas (CV 5.3-12.8%). The citrate concentrations in the artificially depleted plasmas were lower than those in the normal and coumarin plasmas. These differences should be considered in the selection and certification of plasmas as calibrants for local calibration of PT systems. The lyophilized plasmas’ INR values obtained in the present study will be used for a field study of local PT calibration to assess their efficacy.

The Reliability of Manufacturer-determined, Instrument-specific International Sensitivity Index Values for Calculating the International Normalized Ratio

1994 ◽  
Vol 102 (1) ◽  
pp. 128-133 ◽  
Author(s):  
Mark T. Cunningham ◽  
George F. Johnson ◽  
Beverly J. Pennell ◽  
John D. Olson
Keyword(s):  
International Normalized Ratio ◽  
Sensitivity Index ◽  
International Sensitivity Index

How to Generate a More Accurate Laboratory-Based International Normalized Ratio: Solutions to Obtaining or Verifying the Mean Normal Prothrombin Time and International Sensitivity Index

2018 ◽  
Vol 45 (01) ◽  
pp. 010-021 ◽  
Author(s):  
Emmanuel Favaloro
Keyword(s):  
Prothrombin Time ◽  
Vitamin K Antagonists ◽  
Anticoagulation Therapy ◽  
Clinical Importance ◽  
International Normalized Ratio ◽  
Secondary Process ◽  
Sensitivity Index ◽  
Thrombotic Risk ◽  
Laboratory Test Results ◽  
International Sensitivity Index

AbstractAlthough the landscape of anticoagulation therapy is evolving, vitamin K antagonists (VKAs) such as warfarin remain an anticoagulant of choice for many clinicians and their patients. Nevertheless, management of VKA therapy remains challenging, largely because of patient variability and drug and food interactions; thus, VKA dosing has to be personalized. This is achieved by regular monitoring using a test called the prothrombin time (PT), mathematically converted to an international normalized ratio (INR). The INR system is meant to harmonize laboratory test results by taking into account reagent and instrumentation variability that is otherwise expected to give rise to variable PT values, but which should accordingly lead to less variable INR values. Of clinical importance, too low an INR is suggestive of increased thrombotic risk and typically means the VKA dose should be increased, whereas too high an INR is suggestive of increased bleeding risk and typically means the VKA dose should be temporarily withheld and/or decreased. However, evidence continues to show that variability in INR values between laboratories remains unacceptably high. Given that modern instrumentation provides for robust analytical values—meaning highly reproducible intralaboratory clotting times or PTs in this case—the most likely cause of high INR variability is inconsistency in the INR test components—meaning the MNPT (mean normal PT) and ISI (international sensitivity index) values used by laboratories to generate a given INR. In other words, there are doubts as to the accuracy of some INR values because there are corresponding doubts about the accuracy of MNPT and/or ISI values that have been assigned by some laboratories for their reagent/instrument combination. The current report is intended to provide some solutions around the problems of inaccurate INRs, ISIs, and MNPTs, thus aiming to drive laboratory INRs closer to “truth,” and thus promote better patient management. The novel strategies include a primary process of transference to obtain/verify MNPT and/or ISI values for a new reagent using an existing reagent as reference, and a secondary process whereby external quality assessment data can be used to correct bias or existing errors in assigned MNPT and/or ISI values.

A Multi-Centre Study to Evaluate Method Dependency of the International Sensitivity Index of Bovine Thromboplastin

1989 ◽  
Vol 61 (02) ◽  
pp. 166-169 ◽  
Author(s):  
R H M Peters ◽  
A M H P van den Besselaar ◽  
F M F G Olthuis
Keyword(s):  
Oral Anticoagulant Therapy ◽  
Normal Subjects ◽  
International Normalized Ratio ◽  
Sensitivity Index ◽  
Multi Centre Study ◽  
Blood Samples ◽  
Manual Method ◽  
Student’S T ◽  
International Sensitivity Index ◽  
Detailed Protocol

SummaryIn The Netherlands, a particular coagulometer method for prothrombin time (PT) determination with reduced sample and reagent volumes is used by 62% of the laboratories controlling oral anticoagulant therapy. This “micro-method” has been calibrated against the manual tilt-tube technique for PT determination by six Dutch laboratories. Each laboratory tested 20 fresh normal blood samples and 60 fresh patient blood samples using both methods with the same batch of bovine thromboplastin reagent, according to a detailed protocol. Both methods were comparable as to their precision, but PTs measured by the micromethod were significantly prolonged (p <0.001, Student’s t-test) as compared to the manual method. This effect is stronger for samples of normal subjects than for patients’ samples. It was assumed that the International Sensitivity Index (ISI) of the bovine thromboplastin for the manual method was 1.00 in each laboratory. The ISI-values of the bovine thromboplastin for the micro-method determined by the six laboratories ranged from 1.00 to 1.07 (mean 1.03, SD 0.03). Our results indicate that any other laboratory, using this thromboplastin and the micromethod, should obtain accurate assessment of the International Normalized Ratio from their own mean normal PT and an ISI which is 3% higher than the ISI supplied by the thromboplastin manufacturer for the manual tilt-tube method.

scholarly journals Simplified Method for International Normalized Ratio (INR) Derivation Based on the Prothrombin Time/INR Line: An International Study

2010 ◽  
Vol 56 (10) ◽  
pp. 1608-1617 ◽  
Author(s):  
Leon Poller ◽  
Saied Ibrahim ◽  
Michelle Keown ◽  
Albert Pattison ◽  
Jørgen Jespersen
Keyword(s):  
Prothrombin Time ◽  
Independent Set ◽  
International Study ◽  
International Normalized Ratio ◽  
Sensitivity Index ◽  
Concerted Action ◽  
Total Proportion ◽  
The Mean ◽  
Certified Values ◽  
International Sensitivity Index

BACKGROUND The need to perform local International Sensitivity Index (ISI) calibrations and in particular the requirement for a manual method for prothrombin time (PT) determination, have proved to be obstacles to application of the WHO scheme for PT standardization. METHODS We used international normalized ratio (INR) derived with a set of only 5 European Concerted Action on Anticoagulation (ECAA) lyophilized calibrant plasmas, certified manually by expert centers with reference thromboplastins, to determine a local PT/INR Line. We compared results of an independent set of validation plasmas with INRs from conventional ISI calibrations and with manually certified INRs. RESULTS The mean certified INR of 5 lyophilized validation plasmas was 2.41 with human thromboplastin, 2.04 with bovine/combined, and 2.80 with rabbit. With 42 human reagents, the mean observed INR of the validation plasmas was 2.68 (11.2% deviation from certified INR). Deviation was reduced to 0.4% with both local ISI calibration and the PT/INR Line. Eight results based on bovine/combined thromboplastin gave an INR deviation of 4.9%, becoming 0.5% after ISI calibration and 2.4% with the PT/INR Line. Six results with rabbit reagents deviated from certified INR by 2.5%. After ISI calibration, deviation became 1.1%, and with the PT/INR Line, 0.7%. The PT/INR Line gave similar results with both linear and orthogonal regression analysis. The total proportion of validation plasmas giving INR within 10% deviation from certified values was 42.5% with uncorrected INR, which increased to 92.1% with local ISI calibration and 93.2% with the PT/INR Line. CONCLUSIONS The PT/INR Line procedure with 5 ECAA calibrant plasmas successfully substitutes for local ISI calibrations in deriving reliable INRs.

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