Calibration, Quality Control Materials, and Procedures

All automated analyzers should be calibrated according to the manufacturer s recommended methods and performed according to the manufacturer s specifications. The calibration and quality control materials are often of animal or human origin, but they are not currently from the laboratory animal species relevant for toxicology except for some hormones and proteins. Occasionally, some problems arise because of inaccurately calibrant values assigned by the manufacturer. Troponin I assays are an example values were assigned by the various manufacturers (Tate et al. 1999) and the values for calibrant and quality control materials were found to differ markedly between manufacturers. 

Many biochemical analyzers rely on single-point calibration at values that are normal for humans but differ from those of laboratory animals such reliance requires the analyzer to be linear over a range that includes normal and extremely abnormal values as far as practicable. To ensure correct calibration and consistent analyzer performance, quality control materials should be used for every batch of analyses performed. Many laboratories use trilevel materials similar in properties to the calibration materials and with quoted assay values that are relative to low, normal, and high human blood samples. It is good practice to cross-reference new batches of quality control materials with previous batches because there may be slight differences that are sometimes unacceptable and due to shipment and delivery problems. 

To aid control procedures, many laboratories participate in external quality assessment schemes (also termed external proficiency testing). In these assessment schemes, the pools of material may be human or animal in origin and are distributed to a number of participating laboratories for comparative purposes. Given the various analyzer technologies, it is perhaps not surprising that results obtained by various analyzers differ to some extent and these proficiency schemes do alert laboratories to poor performance. 

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