How does IDM calculate from RU to EliA units?

How does IDM calculate from RU to EliA units?

 ug/l x Dilution factor x Correction factor x Lot Specific factor = U/ml 

RU are calculated into the number of IgG antibodies (µg/l) with help of the calibration curve (the calibrators have a defined concentration of antibodies in µg/l). These calibrator concentrations are traceable to WHO standards.


Dilution factor:
This result has to be set into relation to the dilution of the sample. Example: EliA Sm with the instrument dilution of 1:100. The instrument found 300 RU and "translates" this with help of the curve into 9 µg/l. Accordingly, the "real" result for the sample is 900 µg/l. The dilution factor is 100. For ANCA it is 50, for dsDNA it is 10. The individual dilutions of all EliA tests can be found in the "EliA at a glance" table on our product page ».


Correction factor:
We calculate the "real" titre in the original sample when we, anyhow, give out EliA Units. And if we do so, why don't we include this factor into the lot-specific factor? The lot-specific factor is given on the barcode. The barcode can not code an unlimited variation of factors. Thus, the lot-specific factors have to be about in the same range. They are much more in the same range when we compensate the different dilutions. This is done with the correction factor. Thus, all µg/l results are calculated with a correction factor so that they are about in the same level. If you put in another dilution, for example 1:50 for anti-dsDNA, this influences the dilution factor but not the correction factor. Correction factor for dsDNA = 0,1, for Symphony = 0,001, for ANCA 0,02, others = 0,01


Lot-specific factor:
Cut-off of all products shall be 10 EliA Units. If the cut-off is set at 40 µg/l (x100 = 4000 µg/l in the original sample) we have to give a factor, that calculates 40 x factor = 10 (which is a factor of 0,25). This was for example the first lot-specific factor for Sm. In the next lot the cut-off could be at 50, then the factor was 0,2.


EliA on Phadia 250 or Phadia 2500/5000:
For the bigger Phadia instruments, a factor compensates the small difference of SOME EliA parameters between the Phadia 100 results and the Phadia 250 results or Phadia 2500/5000 results, respectively .This "instrument factor" is included in the correction factor. Thus, the correction factor is not 0.01 but for example 0.0112 (for centromere on Phadia 250). You can find the correction factors in the EliA at a glance overview.








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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.