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Test Code THCSM Thyroid Function Cascade, Monitor (without Thyroid Peroxidase Antibody), Serum


Specimen Required


Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1.5 mL

Collection Instructions: Within 2 hours of collection, centrifuge and aliquot serum into a plastic vial.


Secondary ID

622850

Useful For

Monitoring patients diagnosed with thyroid disease

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
FRT4C T4 (Thyroxine), Free, S Yes No
T3C T3 (Triiodothyronine), Total, S Yes No

Testing Algorithm

If thyrotropin (TSH) is less than 0.3 mIU/L, then free T4 (FT4, thyroxine) will be performed at an additional charge.

 

If free T4 is normal and the TSH is less than 0.1 mIU/L, then T3 (triiodothyronine) will be performed at an additional charge.

 

If TSH is greater than 4.2 mIU/L, then free T4 will be performed at an additional charge.

Method Name

Electrochemiluminescent Immunoassay (ECLIA)

Specimen Type

Serum

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 7 days
  Frozen  30 days
  Ambient  72 hours

Reject Due To

Gross hemolysis Reject
Gross lipemia OK
Gross icterus OK

Reference Values

0-5 days: 0.7-15.2 mIU/L

6 days-2 months: 0.7-11.0 mIU/L

3-11 months: 0.7-8.4 mIU/L

1-5 years: 0.7-6.0 mIU/L

6-10 years: 0.6-4.8 mIU/L

11-19 years: 0.5-4.3 mIU/L

≥20 years: 0.3-4.2 mIU/L

Interpretation

In primary hypothyroidism, thyrotropin (TSH) levels will be elevated. In primary hyperthyroidism, TSH levels will be low.

 

The ability to quantitate circulating levels of TSH is important in evaluating thyroid function. It is 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.

 

Elevated or low TSH in the context of normal free thyroxine is often referred to as subclinical hypo- or hyperthyroidism, respectively.

 

Thyrotropin-releasing hormone (TRH) stimulation differentiates all types of hypothyroidism by observing the change in patient TSH levels in response to TRH. Typically, the TSH response to TRH stimulation is exaggerated in cases of primary hypothyroidism, absent in secondary hypothyroidism, and delayed in tertiary hypothyroidism. Most individuals with primary hyperthyroidism have TSH suppression and do not respond to TRH stimulation test with an increase in TSH over their basal value.

 

Patients who are sick and hospitalized may have falsely-low or transiently-elevated TSH levels.

Method Description

The cobas e immunoassay thyrotropin (TSH) method employs monoclonal antibodies specifically directed against human TSH. A biotinylated monoclonal TSH-specific antibody and a monoclonal TSH-specific antibody labeled with a ruthenium complex react to form a sandwich complex. After the addition of streptavidin-coated microparticles, the complex becomes bound to the solid phase via interaction of biotin and streptavidin. The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Application of a voltage to the electrode then induces chemiluminescent emission, which is measured by a photomultiplier.(Package insert: Elecsys TSH. Roche Diagnostics; V4.0, 02/2023)

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 to 2 days

Specimen Retention Time

7 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information

84443

84439-(if appropriate)

84480-(if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
THCSM Thyroid Cascade (Monitor), S 11579-0

 

Result ID Test Result Name Result LOINC Value
STSHM TSH, Sensitive, S 11579-0