Why Standard Reference Ranges Differ From Lab to Lab

Laboratory reference ranges can vary depending on the lab, method of assessment, and the health of the population in the area where the reference ranges were established. Each lab establishes its own reference ranges/intervals, and they are designed to reflect what is typical based on age, gender, and other factors.

Minor discrepancies seen between lab reference ranges can be due to a different standard deviation from the mean used in their sample set. More considerable differences can be due to different analytical methodologies, testing equipment, or even different reagents used by the lab itself. A lab may also cite references established by test manufacturers. Reference populations should be made up of at least 120 subjects and usually reflect the middle 95% of results for that population. It is important to note that disease and dysfunction may be present even when results fall within the conventional or standard range (Testing.com).

Lab discrepancies can be observed when evaluating free testosterone or thyroid antibody studies. Although the units remain the same, the reference intervals used by the major commercial labs Quest and LabCorp can be notably different. For example, Quest calculates free testosterone based on total testosterone, SHBG, and albumin and reports in pg/mL. LabCorp also reports in pg/mL but uses a direct, analog immunoassay method with a distinctly different reference range than Quest. Reference ranges for thyroid antibodies also differ significantly between Quest and LabCorp. Click here to read an article on why there are discrepancies between labs reporting thyroid antibodies.

CLICK HERE for an article on The Shortcomings of Standard Reference Ranges.

References

Ceriotti, Ferruccio, and Joseph Henny. “"Are my Laboratory Results Normal?" Considerations to be Made Concerning Reference Intervals and Decision Limits.” EJIFCC vol. 19,2 106-14. 16 Oct. 2008

Costello, Rebecca B et al. “Perspective: The Case for an Evidence-Based Reference Interval for Serum Magnesium: The Time Has Come.” Advances in nutrition (Bethesda, Md.) vol. 7,6 977-993. 15 Nov. 2016, doi:10.3945/an.116.012765 

LabCorp Free Testosterone https://www.labcorp.com/tests/144980/testosterone-free-direct. Thyroid Antibodies https://files.labcorp.com/testmenu-d8/sample_reports/006684.pdf

Lamers, Yvonne. “Approaches to improving micronutrient status assessment at the population level.” The Proceedings of the Nutrition Society vol. 78,2 (2019): 170-176. doi:10.1017/S0029665118002781   0

Merck Manual Professional Version. Normal Laboratory Values. https://www.merckmanuals.com/professional/resources/normal-laboratory-values/normal-laboratory-values

NIH. What are blood tests.? https://www.nhlbi.nih.gov/health/blood-tests

Pagana, Kathleen Deska, et al. Mosby's Diagnostic and Laboratory Test Reference. 15th ed., Mosby, 2021.

Quest Diagnostics Free Testosterone. https://testdirectory.questdiagnostics.com/test/test-detail/18944/testosterone-free?cc=MASTER

Thyroid antibodies https://testdirectory.questdiagnostics.com/test/test-detail/7260/thyroid-peroxidase-and-thyroglobulin-antibodies?cc=MASTER

Testing.com formerly American Association for Clinical Chemists Lab Tests Online. Reference Ranges and What They Mean. https://www.testing.com/articles/laboratory-test-reference-ranges/