Why is the EliA upper limit of the measuring range given with ">"?
The upper limit of the measuring range for EliA is lot-specific!
The measuring range for EliA is limited at the upper end (usually) by the highest calibrator:
EliA IgG System: CAL-6 is 600µg/l
EliA IgA System: CAL-6 is 80µg/l
EliA IgM System: CAL-6 is 1000µg/l
EliA Calprotectin System: CAL-6 is 750ng/ml
But how does this transfer to the measuring range for a specific product in EliA Units?
For the calculation of the concentration in EliA Units (full explanation see here) the lot-specific factor is relevant. Thus, the actual upper limit for an EliA test is lot-specific, depending on the value of the factor. But we are required to give a limit in the DfU, and we also want to guarantee a certain measuring range. Therefore, we have limits in which the lot-specific factor can vary. In this case, we have the general limit that the lot specific factor can only decrease 20% from the usual lot-specific factor (master factor, defined during validation). The limit in the DfU is calculated on this lowest allowed lot factor, because it means that we cannot relese any batch for which the upper limit of the measuring range will be lower than this limit in the DfU. That is also why we give the limit in the DfU with ">" because usually the detection limit for any batch at the customer will be higher than this value.
Master factor: 0.50
Lowest allowed lot-specific factor: 0.40
detection limit in the DfU: ">240 U/ml"
(600 µg/l x 0.40 = 240 U/ml)
detection limit for a batch with factor 0.48: 288 U/ml
(600 µg/l x 0.48 = 288 U/ml)
So, results between 240 and 288 will still be given with actual, correct, numeric concentration results. Only results above 288 U/ml will be reported as "ABOVE".
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