Let’s explore “Total T3 — lab reference”

Adult interval. Pregnancy and pituitary disease require different interpretation.

Binding abnormalities and severe illness may affect some free-hormone assays.

Assay-specific. Positive result supports thyroid autoimmunity but does not determine treatment alone.

Assay-specific. Also affects thyroglobulin tumor-marker interpretation.

Use the exact assay cutoff. Helpful in selected Graves disease questions.

Not a general thyroid wellness target. Use tumor follow-up, thyroid anatomy, and antibody status.

Morning fasting collection is preferred when practical. Day-to-day variation is substantial.

Negative acute-phase reactant; affected by liver function and nutrition.

Calculated from iron and TIBC. Fasting and timing improve consistency.

Acute-phase reactant. Menstruation, menopause, inflammation, liver disease, and iron therapy matter.

<150 supports deficiency; 150-400 is often treated as borderline and may warrant MMA/homocysteine review.

<4.0 suggests deficiency. Recent intake or supplementation may raise serum values.