Thyroid Function Test Pattern Interpreter

It compares TSH, Free T4 and optional Free T3 with the same laboratory report’s intervals and organizes the combination into a descriptive biochemical pattern for stable, nonpregnant adults. It does not establish a diagnosis, cause or treatment.

Intervals vary with assay, laboratory and population. Enter each result and both limits in the exact unit printed on the same report; this page does not prefill or substitute a generic interval.

For this interpreter, TSH and Free T4 are required inputs. Free T3 is required to resolve the low-TSH / within-range-Free-T4 branch into subclinical hyperthyroid versus T3-thyrotoxicosis biochemical patterns. This is a computational requirement, not a clinical testing rule: NICE NG145 recommends Free T4 and Free T3 when TSH is below the reference range in the adult testing cascade. Free T3 is therefore not clinically unnecessary in other low-TSH states.

It is a biochemical pattern commonly compatible with primary hypothyroidism, but a single pattern does not establish cause, chronicity or whether treatment should begin.

It is a subclinical hypothyroid biochemical pattern. Persistence, degree of TSH elevation, symptoms, age, pregnancy status, medicines and underlying thyroid disease affect its significance.

Low TSH with high Free T4 is a thyrotoxicosis pattern. Low TSH with Free T4 within range and high Free T3 is a T3-thyrotoxicosis pattern. Neither pattern identifies the cause or selects treatment.

It may occur with central hypothyroidism, non-thyroidal illness, medicines, recent treatment or recovery. A normal TSH does not exclude central hypothyroidism; pituitary context and other axes require clinical assessment.

No. TSH and Free T4 within the submitted ranges do not override symptoms or prior disease, and a TSH within range cannot exclude central hypothyroidism when Free T4 is low.

Biotin, heterophile antibodies, macro-TSH, antistreptavidin or antiruthenium antibodies, thyroid-hormone autoantibodies and method-specific effects may cause falsely high or low results. Discordance should prompt laboratory-method review rather than automatic diagnosis.

Glucocorticoids, dopamine, amiodarone, lithium, levothyroxine timing or adherence, antithyroid treatment, acute non-thyroidal illness, radioactive iodine, surgery and recovery can alter results. A new dose or treatment may not yet be at steady state.

No. Pregnancy, preconception, postpartum care, children, adolescents, neonatal testing and acute or critical illness need dedicated intervals and pathways. The 2026 ATA pregnancy guideline replaces the older 2017 pregnancy guidance for those settings.

No. It only describes values against supplied intervals. It cannot diagnose thyroid disease, determine etiology, recommend a medicine or dose, or replace history, examination, repeat testing, antibodies, imaging or pituitary assessment.