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TSH (3rd Generation) with Reflex to FrT4

TSH (3rd Generation) with Reflex to Free T4, Directed TSH, dir-TSH, TSH, Directed, TSH Reflex, Reflex TSH, Free T₄ Reflex, Reflex FT₄

Test Codes

EPIC: LAB6903, Beaker: TSHR1

Department

Chemistry

Instructions

When a TSH with Reflex to FrT4 is ordered the Laboratory will first perform the TSH assay and then automatically reflex the patient sample for a Free T₄ assay result when appropriate. TSH with Reflex to FrT4 will provide physicians a convenient and economical screening option:

• For patients with normal TSH results (see Reference Range below), TSH values will be reported and the Free T₄ assay will not be performed. The following comment will appear in the report: "TSH result within reference range, Free T₄ not performed."
• For patients with abnormal TSH results (see Reference Range below), the Free T₄ assay will automatically be performed and the report will include the abnormal TSH and Free T₄ result.

Specimen Collection Criteria

Collect: One Gold-top SST tube (adults) or one full Gold-top Microtainer^® (pediatric). (Minimum Whole Blood 4.0 mL)

Contact the Laboratory for the acceptability of other tube types.
See Minimum Pediatric Specimen Requirements for Microtainer^® collection.

Physician Office/Draw Specimen Preparation

Let SST specimens clot for 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged SST tube within two hours of collection. (Minimum: 1.0 mL)

Preparation for Courier Transport

Transport: Centrifuged SST tube, refrigerated (2-8°C or 36-46°F). (Minimum: 1.0 mL)

Rejection Criteria

• Grossly hemolyzed specimens.
• Red-top tubes with serum not separated from cells within two hours of collection. 

In-Lab Processing

Let SST specimens clot 30-60 minutes. Centrifuge SST tubes or Microtainers^® to separate serum from cells. Deliver immediately to the appropriate testing station.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 7 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Dearborn Chemistry Laboratory
Farmington Hills Chemistry Laboratory 
Grosse Pointe Chemistry Laboratory 
Royal Oak Automated Chemistry Laboratory 
Troy Chemistry Laboratory
Taylor Chemistry Laboratory
Trenton Chemistry Laboratory
Wayne Chemistry Laboratory 

Performed

Sunday – Saturday, 24 hours a day.
Results available within 24 hours of receipt in the Chemistry Laboratory.

Reference Range

TSH (3rd Generation)

1 - 2 days:	3.20 - 34.60 mcIU/mL.
3 - 4 days:	0.70 - 15.40 mcIU/mL.
5 days - 4 weeks:	1.70 - 9.10 mcIU.mL.
1 month - 11 months:	0.80 - 8.20 mcIU/mL.
1 year - Adult:	0.40 - 4.50 mcIU/mL.

TSH (3rd Generation) Pregnancy

1st Trimester:	0.26 - 2.66 mcIU/mL
2nd Trimester:	0.55 - 2.73 mcIU/mL.
3rd Trimester	0.43 - 2.91 mcIU/mL.

FT4

0-9 Days: 0.5-1.7 ng/dL.

10 Days - Adult: 0.7-1.5 ng/dL.

FT4 Pregnancy

1st Trimester: 0.7-1.5 ng/dL.

2nd Trimester: 0.5-1.0 ng/dL.

3rd Trimester: 0.5-1.0 ng/dL.

Test Methodology

Chemiluminescence.

Interpretation

Hypothyroidism	Elevated TSH and low FT4 substantiated by clinical correlation.
Hyperthyroidism	Depressed TSH and elevated FT4 substantiated by clinical correlation.
Subclinical Hypothyroidism	Slightly elevated TSH and normal FT4.
Subclinical Hyperthyroidism	Slightly depressed TSH and normal FT4.

Heterophilic antibodies in human serum can react with reagent immunoglobulins, interfering with in vitro immunoassays. Patients routinely exposed to animals or animal serum products can be prone to this interference and anomalous high values can be observed. Additional information may be required for diagnosis.

Clinical Utility

• TSH with Reflex to FrT4 is an additional option for screening relatively healthy patient populations. TSH and free T₄ requests can still be ordered independently. Physicians can choose the most appropriate test sequence for screening, monitoring and managing the thyroid status of their patients.
• TSH levels aid in evaluating thyroid function and replacement therapy. They are especially useful in the differential diagnosis of primary (thyroid) from secondary (pituitary) and tertiary (hypothalamus) hypothyroidism. In primary hypothyroidism, TSH levels are significantly elevated, while in secondary and tertiary hypothyroidism, TSH levels are low or normal.
• When testing patients on thyroid hormone replacement, blood should be obtained shortly before the patients next dose. Testing shortly after thyroid hormone intake should not affect TSH results, however it may result in an apparently elevated free T₄. If a patient's dose of thyroid hormone is changed, it is recommended that 6-8 weeks be allowed to elapse before retesting.

CPT Codes

84443

Contacts

Last Updated

10/23/2023