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Test Code TSHCA Thyroid Function Cascade , Plasma or Serum

Additional Codes

Ordering Mnemonic




Reflex Information:

1. If TSH is <0.10, a Free T4 is reflexed. If the FT4 is normal, a T3 total is reflexed.

2. If the TSH is 0.10-0.33, a Free T4 is reflexed.

3. IF the TSH is 0.34-5.10, no further testing is reflexed.

4. If the TSH is >5.10, a Free T4 and a TPO Antibody is reflexed.

Performing Laboratory

Holland Hospital Laboratory Services

Specimen Requirements

Submit only 1 of the following specimens:



Container/Tube: Mint-top (lithium heparin) tube

Specimen Volume: 1 mL of plasma

Collection Instructions:

Note: 1. Indicate plasma.

2. Label specimen appropriately (plasma).



Container/Tube: Serum gel tube

Specimen Volume: 1 mL of serum

Collection Instructions:

Note: 1. Indicate serum.

2. Label specimen appropriately (serum).

Specimen Transport Temperature

Refrigerate ≤48 hours/Frozen OK

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding


84439-T4 free (if appropriate)

Reference Values

0.34-5.1 µIU/mL