Quite frequently it is discussed here why different labs/assays have different reference ranges.
Trying to provide some background why the comparison of lab values is pointless without considering the individual method specific reference range.
Lets take T3 as an example:
Basically two different assay types exist (also true for T for example): the immunoassay type (e.g. RIA, ECLIA) and the LC-MS based assay
LC-MS is considered the golden standard nowadays as it provides the highest specificity combined with a very good sensitivity. The variability of an LC-MS assay is typically somewhere around 10 to 15% (sometimes the 95% confidence interval is stated, ie 95% of the measurements are within this variability - thats an expression of the precission of the assay).
Lets look at the graph below. Its shows the repeat measurements of the same sample using many different assays (x axis). The mean of the reference method (MS) and the 95% confidence interval is indicated by the dotted line.
Assay C for example behaves highly comparable with the MS method, both in terms of accuracy (comparable means) and precision (comparable variability). Results are therefore highly comparable and a reference range established for the MS method might also be applicable for assay C.
Assay B, K or J for example show a very different response. They systematically overestimate the sample and a reference range determined by the MS method is definitly not applicable for these assays.
So how are reference ranges then established for assay K for example?
- Either the lab of the supplier of the assay provides a reference range which is based on a large number of healthy patients - do directly established reference range using this method
- Or the lab/supplier of the assay crossvalidates the assay to a reference method. Basically samples representing the lower and the higher ref range of the MS method are taken and these samples are measured multiple times with assay K. So the ref range for the MS method can be 0.5 to 2.5 which could translate do a ref range for assay K of 1.2 to 3.0 (numbers are just examples; even the slope of the assay - so how sensitive the assay responds to different concentrations can be different).
Hope that helps
Figure taken from