Lab Information Manual

Laboratory:

Clinical Biochemistry (AUTOMATED)

Test Name:

THYROID STIMULATING HORMONE (TSH) - (P)

Test Code: TSH

Clinical Information:

Description: TSH should be the initial test to screen for clinically-suspected hypothyroidism or hyperthyroidism.

TSH is always measured with reflex based on age-specific reference intervals to FT4 and FT3 when criteria are met. For example, in adults following algorithm is used:

TSH	Clinical	Reflex
TSH	Clinical	FT4	FT3
0.4 – 4.2 mU/L ^a	Euthyroid	Not performed	Not performed
0.1 – 0.3 mU/L	Possible hyperthyroidism	Performed	Not performed
<0.1 mU/L	Overt hyperthyroidism	Performed	Performed
>4.2 mU/L	Possible hypothyroidism	Performed	Not performed

^a Algorithm for adults is shown, in pediatrics age-appropriate thresholds are used.

TSH is sensitive and specific marker for the assessment of thyroid disease in patient with intact pituitary-thyroid axis. Very slight changes in circulating free T4 and free T3 levels result in much greater opposite changes in TSH level.

Repeat testing of TSH should be limited to a period greater than 6 weeks, except in pregnant patients

Ordering FT4 and/FT3 outside of reflex testing is restricted. For more details see:

THYROXINE, FREE (FREE T4, FT4) - (P)

TRIIODOTHYRONINE, FREE (Free T3, FT3) - (P)
Patient Preparation Instructions: This test is unaffected by multivitamins (45–125 µg biotin) or biotin-only supplements.

For additional information see:

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

Manitoba Testing Endocrine Testing Guidelines 2022

Policy Statement - Drug Screen TSH VitB12 ordering in the ED- 15 May-2018

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

Ambient: 7 days

Refrigerated: 14 days

Frozen: 2 years, 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 Biochemistry Hematology Requisition (R250-10-92)

_SH Hospital Biochemistry Hematology Non Winnipeg Brandon (R250-10-91)

_SH Winnipeg Brandon Biochemistry Hematology Requisition (R250-10-94)

_SH Winnipeg Brandon Hospital Biochemistry Hematology Requisition (R250-10-93)

Reference Values:

Reference Intervals:

Age	TSH, mU/L
<8 days	1 – 39
8 days - < 5 weeks	1.7 – 9.1
5 weeks - <1 year	0.8 – 8.2
1 – 20 years	0.7 – 5.7
³ 21 years	0.4 – 4.2

Reference Intervals during Pregnancy (not on patient reports)

1^st trimester	0.3 - 4.6 mIU/L
2^nd trimester	0.3 - 4.1
3^rd trimester	0.2 - 3.2

Method of Analysis:Roche Electrochemiluminescence

Availability:

Daily