Analyzers and Methodology

When an analyzer is acquired, there should be an installation qualification (IQ) and an operational qualification (OQ). The supplier will normally carry out installation procedures and ensure the analyzer is properly installed (IQ), and this requires documentation for GLP purposes (CLSI/GP31-P). For operational qualification, a number of analytical issues must be addressed by the users to ensure the performance of the analyzer and that the methods to be utilized are characterized and documented. There are several international guidelines for analyzer evaluations and laboratory practice some of them, provided by the Clinical Laboratory and Standards Institute (CLSI), are referenced at the end of this chapter 

Imprecision of a method (more widely described as precision) is described by a numerical value (often expressed as standard deviation—SD—or coefficient of variation—CV%) obtained from a series of replicate measurements it is a measure of the closeness of agreement between independent test/measurement results obtained under stipulated conditions (CLSI EP05-A2 EP13-R). 

For each method, the laboratory should establish data that reflect the relative precision (or imprecision). Within-run (or batch) precision is the variability found when the same material is analyzed repetitively in the same analytical run or, alternatively, when duplicate analyses are made within an analytical batch. This can be extended to within-day precision and then further to day-to-day or between-day (or both/ between batches) precision measurement when the variability found is for the same material analyzed on different days. 

Accuracy (or inaccuracy or the less frequently referred-to trueness) describes the numerical value of the difference between the means of series of replicate values or a single measurement and the true value of the analyte or measurand. Sometimes this difference is referred to as bias or systematic error (CLSI EP15-A2). Inaccuracy remains a major challenge for biochemical measurements with laboratory animal 

Analytical specificity relates to accuracy and the ability to determine the analyte exclusively without being affected by other substances. Analytical sensitivity is described by the slope of the calibration curve and the ability of an analytical procedure to produce a signal for a defined change of unit. The terms sensitivity and specificity for analytical procedures have different definitions when applied to diagnostic procedures (see Chapter 14), and they should not be confused. 

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