scholarly journals Local Calibration of International Normalised Ratio Improves between Laboratory Agreement: Results from the UK National External Quality Assessment Scheme

1999 ◽  
Vol 81 (01) ◽  
pp. 60-65 ◽  
Author(s):  
I. Jennings ◽  
T. A. L. Woods ◽  
F.E Preston ◽  
S. Kitchen ◽  
Keyword(s):  
External Quality Assessment ◽  
Local System ◽  
Calibration Graph ◽  
Calibration Model ◽  
Local Calibration ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Measurement Systems ◽  
International Normalised Ratio ◽  
The Uk

SummaryIn the present study we have performed local calibration of International Normalised Ratio (INR) measurement systems in a large series of laboratories. We assigned INRs to five lyophilised plasma calibrants, one prepared from normal plasma and four using plasma from war-farinised patients, using different International Reference Preparations for Thromboplastin. These five calibrants, and two lyophilised test plasmas were analysed by 349 centres using 60 different thromboplastin instrument combinations.Plasma calibrants were assigned INRs using the WHO reference thromboplastin RBT-90 or the European reference thromboplastin CRM 149R. Each participating centre determined PTs of the calibrants with their local system. These PTs were then used to construct a local calibration graph relating PT to INR. The PTs of test plasmas were converted directly into INR using the local calibration model and into INR using the conventional method. The overall medians of conventionally derived INRs of two test plasmas analysed in 349 centres were 2.50 and 3.10, compared to 2.47 and 3.04 after local calibration where RBT-90 was employed to assign INRs to calibrants. Use of CRM 149R to assign INRs to calibrants led to a significant (p <0.0001) increase in INR to 2.7 and 3.36 respectively. When results were grouped according to the thromboplastin employed, agreement between results with different reagents was improved by local calibration. There was a significant reduction (p <0.01) in the spread of results in different centres as indicated by a reduction in coefficient of variation.

Thromboplastin Related Differences in the Determination of International Normalised Ratio: A Cause for Concern?

1994 ◽  
Vol 72 (03) ◽  
pp. 426-429 ◽  
Author(s):  
S Kitchen ◽  
I D Walker ◽  
T A L Woods ◽  
F E Preston
Keyword(s):  
Patient Management ◽  
External Quality Assessment ◽  
Oral Anticoagulant Therapy ◽  
Warfarin Dosage ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
International Normalised Ratio ◽  
The Uk ◽  
The Relationship

SummaryWhen the International Normalised Ratio (INR) is used for control of oral anticoagulant therapy the same result should be obtained irrespective of the laboratory reagent used. However, in the UK National External Quality Assessment Scheme (NEQAS) for Blood Coagulation INRs determined using different reagents have been significantly different.For 18 NEQAS samples Manchester Reagent (MR) was associated with significantly lower INRs than those obtained using Diagen Activated (DA, p = 0.0004) or Instrumentation Laboratory PT-Fib HS (IL, p = 0.0001). Mean INRs for this group were 3.15, 3.61, and 3.65 for MR, DA, and IL respectively. For 61 fresh samples from warfarin-ised patients with INRs of greater than 3.0 the relationship between thromboplastins in respect of INR was similar to that observed for NEQAS data. Thus INRs obtained with MR were significantly lower than with DA or IL (p <0.0001). Mean INRs for this group were 4.01, 4.40, and 4.59 for MR, DA, and IL respectively.We conclude that the differences between INRs measured with the thromboplastins studied here are sufficiently great to influence patient management through warfarin dosage schedules, particularly in the upper therapeutic range of INR. There is clearly a need to address the issues responsible for the observed discrepancies.

Calibration of Local Systems with Lyophilized Calibrant Plasmas Improves the Interlaboratory Variability of the INR in the Italian External Quality Assessment Scheme

1999 ◽  
Vol 82 (12) ◽  
pp. 1621-1626 ◽  
Author(s):  
Veena Chantarangkul ◽  
Bruno Cesana ◽  
Pier Mannuccio Mannucci ◽  
Armando Tripodi
Keyword(s):  
Quality Assessment ◽  
Statistical Approach ◽  
External Quality Assessment ◽  
Geometric Mean ◽  
Local System ◽  
Sensitivity Index ◽  
Local Calibration ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Interlaboratory Variability

SummaryCalibration with lyophilized calibrant plasmas certified in terms of PT with International Reference Preparations for thromboplastin has been proposed to minimize the effect of coagulometers on the INR. Aim of this study was to test the ability of local calibration with lyophilized calibrant plasmas, combined with a modified statistical approach, to improve the interlaboratory variability of the INR measured on two test plasmas (one coumarin and one artificially-depleted) by participants in the External Quality Assessment Scheme (EQAS). Sets of lyophilized calibrant and test plasmas were sent to the participants in the EQAS, who were asked to determine PT with their own reagent/ instrument combination (local system). Results were returned as PT together with information on the type of local system, the stated International Sensitivity Index (ISI) and the geometric mean of PTs determined by testing with the local system fresh plasmas from 20 healthy subjects. Ninety-two participants using 9 and 11 brands of reagents and instruments returned results. The CV of the INR determined with the stated ISI for the coumarin (Mean INR = 4.39) and artificially-depleted (Mean INR = 4.23) test plasmas were 11.2% and 10.3% and were reduced on the average by 34% and 54%, respectively, when the INR was calculated with the local ISI.In conclusions, results from this field study involving laboratories and testing systems representative of the real situation in oral anticoagulant monitoring in our country, indicate that local calibration by artificially-depleted plasmas, combined with the proposed statistical approach, is suitable to improve the interlaboratory agreement on the INR.

scholarly journals Assays for Follicle Stimulating Hormone and Luteinising Hormone: Guidelines for the Provision of a Clinical Biochemistry Service

1987 ◽  
Vol 24 (3) ◽  
pp. 246-262 ◽  
Author(s):  
G H Beastall ◽  
K M Ferguson ◽  
D ST J O'reilly ◽  
J Seth ◽  
B Sheridan
Keyword(s):  
Quality Assessment ◽  
Luteinising Hormone ◽  
External Quality Assessment ◽  
Follicle Stimulating Hormone ◽  
In Vitro Fertilisation ◽  
Similar Proportion ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
The Uk ◽  
Stimulating Hormone

The measurement of serum follicle stimulating hormone (FSH) and luteinising hormone (LH), together with the appropriate sex steroid, is of great value in the investigation of delayed and precocious puberty, hypogonadism, subfertility, polycystic ovarian disease and hypothalamic-pituitary disorders. Dynamic function testing of the hypothalamic-pituitary-gonadal axis should be restricted to a few defined situations. Sequential LH measurements, either in serum or in urine, may be used to time ovulation during artificial insemination or in vitro fertilisation programmes. No special precautions are necessary when sampling for FSH and LH measurement; serum is preferred to plasma and should be stored frozen before assay. Aliquots of timed urine specimens of known volume should be stored frozen without preservative. Gonadotropin results should be available within 2–3 weeks; laboratories unable to meet this schedule are advised to send their samples to a Regional Centre for assay. Reagents for the radioimmunoassay of FSH and LH are readily available, and standard techniques have been developed for their use. Laboratories using ‘in-house’ methods should pay particular attention to the matrix used for preparing standard solutions, the purification of radioligands and the optimisation of the separation system. Low cost matched reagents of proven performance are available in kit form from the Chelsea Hospital for Women; several commercial kits are also available, although few are widely used in the UK. The overall performance of laboratories in the UK External Quality Assessment Scheme (EQAS) for FSH and LH has remained steady for several years. Of the 130 participants, only about 15% in each scheme have ‘good’ performance (cumulative bias less than 10%, plus cumulative variability of bias less than 10%), whilst a similar proportion have ‘unacceptable’ performance (cumulative bias greater than 20% and/or cumulative variability of bias greater than 25%). The remaining 70% of laboratories have ‘adequate’ performance but are at risk of producing results that are clinically misleading. Within any one method group, the performance of FSH and LH assays are closely related. Optimal assay performance depends upon sensible laboratory management to ensure skilled operators, a regular programme of reagent/kit renewal, comprehensive internal and external quality assessment, and attention to detail in all aspects of gonadotrophin assay. The working range of each individual assay should be defined and no absolute result reported from outside this range. Mean intra-assay and interassay coefficients of variation on selected human serum quality control pools should be better than 8% and 15%, respectively, for both gonadotrophins. All laboratories performing FSH and LH assays should belong to the UK EQAS for gonadotrophins. Immunometric assays, using monoclonal antibodies, will supersede radioimmunoassays for FSH and LH during the next few years. Some of these assays will have non-isotopic labels.

scholarly journals Quality of Performance of Assays for Maternal Serum Alphafetoprotein in the United Kingdom: Evidence from the UK External Quality Assessment Scheme 1980–87

1988 ◽  
Vol 25 (3) ◽  
pp. 310-318 ◽  
Author(s):  
J Seth ◽  
I Hanning ◽  
R R A Bacon ◽  
W M Hunter
Keyword(s):  
Neural Tube ◽  
External Quality Assessment ◽  
Maternal Serum ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Laboratory Performance ◽  
The United Kingdom ◽  
Assay Performance ◽  
The Uk

Between-laboratory agreement in the UK EQAS for maternal serum alphafetoprotein has improved steadily since 1976 and the geometric coefficient of variation is now 8 to 9% at levels of 50 to 150 kU/L. The use of a common standard and commercial assay kits appear to have contributed to this trend. Within-laboratory performance is also generally good, about 50% of participants maintain a bias of less than 5%, together with a scatter of the bias of less than 10%. These data indicate that the quality of assay performance is adequate for the requirements of screening programmes for open neural tube effects. The improvement in laboratory performance is such that between-laboratory agreement is better expressed in kU/L than as multiples of the median. Errors in interpretation of clearly normal or abnormal results appear to be rare (0·4%), and contribute little to overall false positive and negative rates. However. they assume significance as most arc due to avoidable errors.

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