Thyroid Panel Interpreter

This calculator classifies three thyroid lab values -- TSH, Free T4, and Free T3 -- against commonly cited reference ranges and combines TSH and Free T4 into a likely diagnosis. Each hormone is judged independently against its own range: TSH against 0.4-4.0 mIU/L, Free T4 against 0.8-1.8 ng/dL, and Free T3 against 2.3-4.2 pg/mL, so raising TSH into the high range never affects the Free T4 Status classification, and raising Free T4 never affects TSH Status -- the three status outputs are computed independently, with no cross-talk between them. The Likely Diagnosis output, however, only looks at TSH and Free T4: high TSH with low Free T4 reads as primary hypothyroidism, low TSH with high Free T4 reads as primary hyperthyroidism, and an isolated TSH abnormality with a normal Free T4 reads as subclinical hypo- or hyperthyroidism. Free T3 plays no role at all in Likely Diagnosis -- it only feeds its own Free T3 Status classification -- which matters clinically because a low or high Free T3 with a normal TSH and Free T4 (as in some cases of non-thyroidal illness, or early autonomous nodules affecting T3 preferentially) will not register in the headline diagnosis and needs to be read on its own.

Beyond primary hypo/hyperthyroidism and the two subclinical patterns, this calculator also flags two less common but clinically important discordant patterns: a low Free T4 with a TSH that is not appropriately elevated reads as a possible central (secondary) hypothyroidism, and an elevated TSH paired with an elevated Free T4 reads as a possible TSH-mediated or pituitary-source pattern. This tool covers those six named patterns only -- it does not implement a full clinical differential, and a TSH/Free T4 combination that fits none of them (for example, a low TSH with a low Free T4, or a normal TSH with a high Free T4) is reported as "not clearly classified" rather than defaulted to Normal, and should be reviewed with a clinician alongside the raw values. Real laboratory reference ranges vary somewhat by assay and lab, so these figures are typical, commonly cited ranges rather than a substitute for the specific lab's reported normal range.