Calibrator: How Long is it Stable?

Calibration is a process of verifying, by comparison with a calibrator of known quantity for its accuracy and imprecision within its assay range. The calibration so performed will have validity and has to be repeated at the end of the validity. The stated stability of the calibrator material after reconstitution is 24hrs. Due to this limited stability, calibration per se, becomes a costly process since few parameters might require frequent calibration. With every calibration, new set of calibrators have to be used that would add to the cost of calibration and cost per reportable test. There are no literatures available which have studied calibrator stability beyond the manufacture's stated stability. Since the stability of the analytes are much longer than 24 hours in serum, we wanted to see if the same is applicable in calibrators as the matrix of calibrators is comparable to serum. Calibration data from January 2015 to December 2016 was collected. All calibrators reconstituted for the analytes to be studied were included. We assayed calibrator at day 0 after reconstitution for Glucose, Total cholesterol, Total protein, Iron and Lactate dehydrogenase. The mean at 0 days was compared with the mean for 3 different time intervals beyond 24 hours after storing aliquots at -200C. The calibrator for glucose was stable for up to 8 weeks, total cholesterol for 7 weeks, total protein for 10 weeks, iron for 28 weeks and LDH for 17 weeks.