Precision intraassay

Method precision refers to the variability in measurement of the same sample. There are three main components of method precision repeatability (also known as system or intraassay precision), intermediate precision (also known as inter-assay or intra-laboratory precision), and reproducibility precision (also known as ruggedness, overall or inter-laboratory... 

Repeatability (Precision). Repeatability is a measure of the precision under the same operating conditions over a short interval of time. It is sometimes referred to as intraassay precision. Two assaying options are allowed by the ICH for investigating repeatability ... 

Inter- and Intra-Assay Precision Intraassay precision and accuracy are assessed within one batch (QCs, standards, etc.), whereas interassay precision and accuracy are assessed using separate batches. 

The inter- and intraassay precisions of this method are less than 8% of the coefficient of variation (CV) across the range of the limits of quantification (0.05-10ng/mL). The accuracy (percentage bias) for all spiked control concentrations does not exceed 4%. Same-day turnaround of results for more than 100 samples is possible with this TC/MS/MS method. This method was used to support an acute... 

Prior to sample analysis, a test batch is required if (1) STD and QC pools need to be qualified, (2) there has been a significant lapse in time since any previous analysis, (3) the scientist does not have documentation with the assay or a similar assay. The test batch should contain minimally low, medium, and high QC at six replicates. Dilution QC samples may be included if dilutions are expected during sample analysis. The acceptance of PSAE is the same as described in intraassay precision and accuracy. 

Cystatin C has been measured by immunodiffusion or rocket electroimmunoassay, but the methods are too insensitive, and any form of labeled immunometric assay is too cumbersome and time consuming for the response time required. The most practical approaches described are to use a latex particle-enhanced turbidimetric or nephelometric immunoassay. An intraassay precision of less than 3% can be expected at the upper limit of the reference interval ( 1.00mg/L), with less than 4% for the between-day value. Further, cystatin C measurement appears unaffected by the spectral interferences affecting creatinine assays. ... 

Table 1 Comparison of intraassay precision of ethanoi assay with and without 1-propanoi as internai standard...

Repeatability (also called intraassay precision) is a measure of the ability of an LC method to provide consistent measurements within a given run or sample sequence. It is assessed by measuring the precision of multiple test results and confirming adherence to predefined criteria. 

The determination of precision can divided into three categories, namely repeatability, intermediate precision, and reproducibility. Repeatability, or intraassay within-day precision, is determined when the analysis is performed in one laboratory by one analyst, using one definite piece of equipment, and is performed within one working day. Intermediate precision is obtained when the analysis is performed within a single laboratory by different analysts over a number days or weeks, using different equipment, reagents, and columns. Reproducibility represents the... 

Precision of the reduced CE-SDS method was studied via repeatability (intra-assay) and intermediate precision (inter-assay) studies. Figure 12 shows electropherogram of the intraassay repeatability data, and Table 4 demonstrates the precision of the assay (%RSDs of 0.3, 0.6, and 3.7% for the HC, LC, and non-main species, respectively). 

It is therefore essential that the variability of an assay be known precisely (Ezan and Grassi, 2000). The performance of an assay in terms of accuracy, reproducibility (CV, interassay variation), and repeatability (CV, intraassay variation) should be determined. For an ELISA, accuracy in the range of 85 to 115% of the standard value and CVs in the range of 15 to 20% are common. The assay limit of quantification is then taken as the lowest concentration of analyte that provides CVs under, e.g., <10% and accuracy within, e.g., 15% of the standard value. A discussion of factors leading to imprecision of microarrays will be addressed later. 

Partial Validation. Partial validations are modifications of already validated bioanalytical methods. Partial validation can range from as little as one intraassay accuracy and precision determination to a nearly full validation. Typical bioanalytical method changes that fall into this category include but are not limited to ... 

Intra-assay precision is evaluated by analyzing aliquots of a homogeneous material several times by one person on one day with the same equipment. Each analysis is independent, so the intra-assay precision is telling us how reproducible the analytical method can be. Intraassay variability is greater than instrument variability, because more steps are involved. Examples of specifications might be that instrument precision is <1 % and intra-assay precision is 2%. 

Precision %RSD< 15 % at>3 levels n>5 at each level %RSD<20 % at LLOQ %RSD<20% n=4-7 CV<2.2 % Uncertainty evaluation Coefficient of variation (CV) 1 % Uncertainty of volumetric error 0.3 % Uncertainty of reference standard 0.1 % Uncertainty of weighing 0.5 % Uncertainty of other systematic errors Combined standard uncertainty Coverage factor Expanded uncertainty Relative expanded uncertainty (%) Intraassay CV=2-9 % Interassay CV=4-12%... 

Intralaboratory precision studies are classified as intraassay, where the profile is obtained doing the replication in only one run, using the same batch of reagents, or interassay, where the precision profile is obtained by comparison of runs done on different days. Poorer precision is generally obtained in interassay studies. 

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