Internal quality control

Once a system has been adopted some long-term parameters have to be kept under constant control. These parameters include intra- and inter-assay variability, assay drift, maximal and non-specific binding, and the standard curve characteristics, such as the slope and the dose at 50% curve displacement. Control charts have to be set up and constantly observed in order to distinguish between sporadic and systematic changes in some parameters, the latter being an indication of some modification in the kit (e.g. a change in a reagent lot) or some problem in the equipment. Intra-assay precision is evaluated by calculating the variability of the duplicate determinations. Measuring samples in singlicate does not allow evaluation of this parameter. In our experience testosterone and DHT should always be measured in duplicate, since the intra-duplicate variability at low concentrations is often >10%. Another important parameter is assay drift. By measuring control sera at the beginning and at the end of the assay it can be determined whether the results at the end of the assay have any tendency to be systematically over- or underestimated. This is particularly relevant in ELISAs and methods relying on colorimetric reactions. If such a tendency is discovered, the number of samples which can be measured in one assay should be reduced. As a general rule, if the assay embraces several microtitre plates, calibrators or even entire standard curves should be run in each plate.

Inter-assay precision is checked by using certified control sera with three different testosterone concentrations (low, middle, high) in each assay. Changes in control sera lots have to be recorded. The results obtained in each assay must fall within a pre-determined, allowed range, usually within ±2 SD of the target value, otherwise repeating the assay should be considered. Control sera can give results outside the allowed range sporadically but ideally their variability should oscillate equally on the two sides of the target value. The persistence of results mainly on one side indicates a systematic problem, which, in the example of Fig. 21.4 was identified in the automatic pipettor.

Hair Loss Prevention

Hair Loss Prevention

The best start to preventing hair loss is understanding the basics of hair what it is, how it grows, what system malfunctions can cause it to stop growing. And this ebook will cover the bases for you. Note that the contents here are not presented from a medical practitioner, and that any and all dietary and medical planning should be made under the guidance of your own medical and health practitioners. This content only presents overviews of hair loss prevention research for educational purposes and does not replace medical advice from a professional physician.

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