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Free T3 (fT3) pmol/L → pg/mL

Convert free t3 (ft3) from pmol/L to pg/mL

Sources last checked: 2026-11-03

Free T3 (fT3) pmol/L → pg/mL

Convert free t3 (ft3) from pmol/L to pg/mL

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Converts units only; reference ranges depend on the laboratory, the assay and the patient.

Source: AMA Manual of Style, 11th ed. (Oxford Academic) — Units of measure converter, Table 2: Selected laboratory tests and conversion factors.Open

What is the Free T3 (fT3) pmol/L → pg/mL?

This converter changes free triiodothyronine (fT3) from pmol/L, the SI unit used in the UK, Scandinavia and much of the European literature, into pg/mL, the conventional unit used in the USA, Turkey and many German-speaking laboratories. It divides by 1.536, the factor derived from the molar mass of liothyronine (650.97 g/mol).

When to use it

  • Interpreting an fT3 in pmol/L from a foreign report when the local lab reports pg/mL
  • Following the course of fT3 across labs that use different units
  • Reading US-based textbooks and studies after seeing SI results

When not to use it

  • Total T3 in nmol/L — a different analyte
  • Transferring numerical reference intervals between assay platforms

How it is calculated

fT3 (pg/mL) = fT3 (pmol/L) ÷ 1.536

Clinical pearls and limitations

  • Converts units only; reference ranges depend on the laboratory, the assay and the patient.
  • 1 pmol/L ≈ 0.651 pg/mL.
  • pg/mL and ng/L are numerically identical; some reports use one, some the other.
  • Two decimal places in pg/mL are more than the assay precision supports; one is usually enough for clinical notes.
  • Interpret fT3 together with TSH and fT4; a unit mismatch between the three is a classic source of apparent discordance.

Frequently asked questions

How do I convert fT3 from pmol/L to pg/mL?

Divide by 1.536. Example: 5.0 pmol/L ÷ 1.536 = 3.26 pg/mL; 6.5 pmol/L ÷ 1.536 = 4.23 pg/mL.

Is pg/mL the same as ng/L for fT3?

Yes. 1 pg/mL = 1 ng/L, because both numerator and denominator are scaled by 1000.

Does converting units make two fT3 assays comparable?

No. It only removes the unit difference; method bias between free-hormone immunoassays remains.

Evidence and guidelines

  1. Primary source: AMA Manual of Style, 11th ed. (Oxford Academic) — Units of measure converter, Table 2: Selected laboratory tests and conversion factors.
  2. PubChem compound summary: liothyronine (triiodothyronine) (CID 5920), molecular weight 650.97 g/mol.

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For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.