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At least 73 records · Page 4Linked to original sources
PubMed2002

Evaluation of frozen plasma calibrants for enhanced standardization of the international normalized ratio (INR): a multi-center study.

Local ISI calibration has been proposed to improve INR accuracy and inter-laboratory precision. We evaluated the affect of local PT calibration on INR precision and accuracy using six levels of frozen plasma calibrants prepared and pooled from normal donors and patients stabilized on sodium warfarin (coumarin) based oral anticoagulant therapy (OAT). Reference prothrombin time (PT) and INR values were assigned to these calibrants in accordance with World Health Organization (WHO) procedure using rTF 95 international reference preparation (IRP) of thromboplastin (human recombinant). These calibrants, along with five similarly characterized individual OAT patient plasmas, were distributed to 127 laboratories in a multi-center study. Calibrant plasmas were evaluated and INR's subsequently determined on the 5 OAT test samples using: 1) the ISI and MNPT in place before the study (the local system), 2) the locally calibrated ISI value (local system with ISI calibration) and 3) a PT-INR calibration curve. Precision of INR results improved across the study group using the local system with ISI calibration and the PT-INR calibration curve methods, while accuracy of INR results improved using the PT-INR calibration curve approach only and not the local ISI calibration. The authors conclude that frozen plasma calibrants can be used locally to enhance precision and accuracy of PT results as reported in INR. These calibrants are effective over a range of reagents and instrument combinations. Furthermore, the PT-INR calibration curve appears to be the superior method for local calibration.

Administration, Oral↗
PubMed2006

Modified versus producer milk calibration: mid-infrared analyzer performance validation.

Our objective was to determine the validation performance of mid-infrared (MIR) milk analyzers, using the traditional fixed-filter approach, when the instruments were calibrated with producer milk calibration samples vs. modified milk calibration samples. Ten MIR analyzers were calibrated using producer milk calibration sample sets, and 9 MIR milk analyzers were calibrated using modified milk sample sets. Three sets of 12 validation milk samples with all-laboratory mean chemistry reference values were tested during a 3-mo period. Calibration of MIR milk analyzers using modified milk increased the accuracy (i.e., better agreement with chemistry) and improved agreement between laboratories on validation milk samples compared with MIR analyzers calibrated with producer milk samples. Calibration of MIR analyzers using modified milk samples reduced overall mean Euclidian distance for all components for all 3 validation sets by at least 24% compared with MIR analyzers calibrated with producer milk sets. Calibration with modified milk sets reduced the average Euclidian distance from all-laboratory mean reference chemistry on validation samples by 40, 25, 36, and 27%, respectively for fat, anhydrous lactose, true protein, and total solids. Between-laboratory agreement was evaluated using reproducibility standard deviation (s(R)). The number of single Grubbs statistical outliers in the validation data was much higher (53 vs. 7) for the instruments calibrated with producer milk than for instruments calibrated with modified milk sets. The s(R) for instruments calibrated with producer milks (with statistical outliers removed) was similar to data collected in recent proficiency studies, whereas the s(R) for instruments calibrated with modified milks was lower than those calibrated with producer milks by 46, 52, 61, and 55%, respectively for fat, anhydrous lactose, true protein, and total solids.

Animals↗
PubMed2005

Calibration curves for real-time PCR.

BACKGROUND: Despite the increasing use of real-time PCR in the diagnosis and management of viral infections, there are no published studies adequately addressing the optimum number of calibrators, the number of replicates of each calibrator, and the frequency with which calibration needs to be repeated. This study was designed to address these issues. METHODS: Cycle threshold data (ABI 7700) was collected from >50 consecutive real-time PCR runs for hepatitis B and Epstein-Barr viruses. Our routine calibration curve made from serial 10-fold dilutions run in duplicate was compared with alternative options, including duplicate 100-fold dilutions, inclusion of a low-copy calibrator, and omission of the duplicate determination. Control data were used to examine the use of an average calibration curve made from multiple runs. RESULTS: Use of duplicate serial 10-fold dilutions led to the least imprecision, duplicate 100-fold dilutions had slightly higher imprecision, and calibration curves obtained with singlet measurements showed the greatest imprecision. For patient data, the duplicate 100-fold dilution calibration curve produced results that best matched those from the routine calibration curve. Use of singlet dilutions or inclusion of a low-copy calibrator produced poorer agreement. Variability in controls was lower with a daily calibration curve than with an average calibration curve. CONCLUSIONS: Duplicate 100-fold dilution calibration curves produced equivalent results and the same imprecision as curves with more calibrators, and thus are a valid alternative. Laboratories should carefully evaluate the variability resulting from the use of average calibration curves before adopting this approach.

Calibration↗