Lab Information Manual

Laboratory:

Clinical Biochemistry (AUTOMATED)

Test Name:

TRIIODOTHYRONINE, FREE (Free T3) - (P)

Test Code: FT3

Clinical Information:

Description: FT3 is available as a component of the Thyroid Reflex Testing protocol when TSH is <0.1 mU/L.

Ordering FT3 outside of reflex testing is restricted and can only be ordered using “Specialized Endocrinology Requisition ” by pre-approved physicians. All other requests will be cancelled.

Orders for FT3 received on non-Shared Health requisition should be substituted by THYROID REFLEX TESTING - (P) (if TSH not ordered).

Test Indications: Measurement of FT3 is rarely indicated in suspected thyroid disease.

FT3 may be useful in situations where thyroid disease is suspected clinically and TSH is abnormal, but FT4 is inappropriately normal.

Patient Preparation Instructions: This test is unaffected by multivitamins (45 - 125 µg biotin) or biotin-only supplements.

For additional information see:

Manitoba Testing Endocrine Testing Guidelines 2022

Clinical Practice Change - Endocrine Testing and Specialized Endocrinology Requisition Update 15-May-24

Clinical Practice Change General-Endocrinology-Requisition-and-Endocrine-Testing-Update 15-May-24

Collection Devices:

Preferred Device:	1 - Li Heparin Plasma Separator Tube(s) - Full Tube Collection Li Heparin Plasma Separator Tube(s) - Full Tube Collection Manufacturer: BD (Becton Dickinson) Catalogue #: 367962
Alternate Device:	1 - Serum Separator (SST) Tube(s) - Full Tube Collection Serum Separator (SST) Tube(s) - Full Tube Collection Manufacturer: Becton Dickinson Catalogue #: 367986

Specimen Required:

Plasma: 2.0 mL

Specimen Stability

Refrigerated: 7 days

Frozen: 1 month, freeze only once

Referral:

Shipping & Storage: Samples must be transferred to an aliquot tube and stored/shipped

· Refrigerated if off-site testing to be performed within 48 hours of collection

· Frozen if testing to be performed after 48 hours

See #110-10-05 Serum / Plasma Separation Procedure & Transport

Requisition:

_SH Specialized Endocrinology Requisition (R250-10-77)

Reference Values:

Reference Intervals:

Age	FT3, pmol/L
<8 days	2.2 - 7.4
8 days - < 5 weeks	2.2 - 8.4
5 weeks - <1 year	3.1 - 10.6
1 – 5 years	3.7 - 10.3
6 - 10 years	4.4 - 9.2
11 - 15 years	4.8 - 0.1
16 - 20 years	5.4 - 8.8
³ 21 years	3.7 - 6.9

Reference Intervals during Pregnancy (not on patient reports)

Trimester	FT3, pmol/L
1^st trimester	3.8 - 6.0
2^nd trimester	3.2 - 5.5
3^rd trimester	3.1 - 5.0

Method of Analysis:Roche Electrochemiluminescence

Availability:

Daily