Discrepancies in Thyroid Antibody Ranges

Question:

We use a different lab for our thyroid panels, and very often the clients have thyroid peroxidase and thyroid antiTPO results that are far higher than the reference ranges on the ODX application. The results we have are IU/L and your units are KIU/l. Can you shed some light on this?

Answer:

We are aware that the ranges for thyroid antibodies show considerable variability between labs. I have had conversations with researchers at more than one of these labs as we have had a number of users bring this to our attention.

Thyroid Peroxidase

Thyroid Peroxidase Abs tend to show less variability, which is why we built-in 2 different biomarker references in the software for Quest and LabCorp. 

The best bet is to look at the range from your lab and choose either the Quest or Labcorp biomarker based on a similar range.

For instance, Vibrant America uses a reference range of <34 IU/ml for their Anti-TPO biomarker result, which is the same as Labcorp, so enter the result in the LabCorp Anti-TPO biomarker slot.

Thyroglobulin Antibodies

The Thyroglobulin Antibody result is another result that has discrepancies from lab to lab. Quest and LabCorp, the 2 largest reference labs here in the U.S. are the labs we use for our default units and reference ranges for Thyroglobulin Antibodies in the ODX application. The discrepancy between labs such as Cleveland Heart Lab, Lifelabs in Canada, and Vibrant America comes about because these labs (and other labs across the globe) are using a different analytical system to measure for the presence of Thyroglobulin Antibodies.

Many labs use Roche Immunoassay to detect the presence of Thyroglobulin Antibodies and this method has a different range than the method used by Quest/LabCorp. Quest and LabCorp, use the Beckman Coulter immunometric assay to determine the presence of antibodies to Thyroglobulin. According to this methodology, any result >1.0 indicates the presence of antibodies such that further investigation is warranted. Unfortunately, we cannot convert from a result from the Roche Assay to the result from Quest or Labcorp because we would be comparing apples to oranges. At this point, we cannot adjust ranges based on lab testing companies. We are looking at the possibility of enabling that sometime in the future, but the software was not developed with that level of complexity.

My recommendation is to not enter a value for the Thyroglobulin Antibody into the software but make a notation of the result with ranges, etc. in the "Practitioners Notes" section. This will allow you to draw your client's attention to this while allowing the software to work on the other thyroid biomarkers that you can enter into the program.

The next question that comes up is around the sensitivity of one method over another. The Roche testing methodology used by many labs is as valid, sensitive, and accurate as of the one used by Quest or LabCorp. They are just using a different "normal" value to express the levels of antibodies detected. Unfortunately, they are not interchangeable with the ones used by Quest or LabCorp.

 

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