[Thyrotropin reference range--should it be changed?].
Level 5 - mechanism / opinion, no new human data
Narrative review evaluating clinical literature and guidelines without systematic methodology
What was done
The author reviewed literature and clinical guidelines (including American National Academy of Clinical Biochemistry recommendations) regarding serum thyrotropin (TSH) reference intervals. The review examined whether the standard upper reference limit (4.0–4.5 mIU/L) should be reduced to account for occult chronic lymphocytic thyroiditis, and discussed influencing factors including age, ethnicity, iodine intake, time of phlebotomy, and assay specificity.
What was found
Standard reference ranges established by sensitive assays span 0.2–0.4 to 4.0–4.5 mIU/L, with a right-skewed non-Gaussian distribution. Rigorous selection of reference populations (excluding individuals with personal/family history of thyroid disease, goiter, detectable antibodies, or medications other than estrogen) does not significantly reduce the upper limit. No epidemiological data demonstrate adverse consequences for serum TSH between 3.0 and 5.0 mIU/L, supporting maintenance of the current upper cutoff, though monitoring is warranted for pregnant women and those at risk for future hypothyroidism.
Why it matters
Lowering the diagnostic TSH threshold risks overdiagnosis and unnecessary medicalization. This synthesis supports maintaining current reference boundaries while selectively targeting higher-risk groups, such as pregnant women, for monitoring.
Limits
This is a narrative review with no systematic search methodology, meta-analytic pooling, or quantitative quality assessment. The abstract presents no original primary data, quantitative effect estimates, or study counts.
Cited by
- supports Conventional laboratory reference ranges define normal TSH levels as anywhere between 0.5 and 5.0 mIU/L.