CALIBRATION AND CONTROL GUIDE I

Calibration should be carried out when there is a possibility that the reagents’ behaviour has changed and the results are not comparable to those that were available so far. A calibration should be performed if:

• Reagent kit change: The new kit may have a different state of preservation, or be from a different batch.
• Change of working reagent: Although the reagent comes from the same kit, the new working reagent is different from the previous one and could have some different characteristic (for example, the reaction blank value in the case of R1 or the amount of enzyme of R2).
• When recommended after opening: Open reagents are degrading due to exposure to air, or due to the effect of ambient temperature. Manufacturers can define periods for which calibration is maintained within reasonable values; beyond that time, the risk of the reagent being different in its characteristics increases and a new calibration that «zeroes» the system is recommended.
• When there is evidence that the controls do not give the expected value: Using controls within all the work series allows us to detect any alteration of the reagent if the control deviates from the expected value (for example, beyond 15% per above or below the central value). There are rules to follow the evolution of control values ​​that indicate the need or not to recalibrate the system.
• When the values ​​of target and/or of increments of absorbance are significantly different from the previous results: A signal of deterioration of the reagent is obtained when the value of target is very different, or the variation of absorbance in the reaction is clearly less than expected.

If none of these circumstances occur, it is very possible that calibration is unnecessary.