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TSH Reflex to Free T4
Message*Ask patients about biotin use prior to ordering. Stop Biotin: Discontinue all biotin supplements (often found in multivitamins, hair/skin/nail formulas, energy drinks) for at least 2-3 days (ideally 3-5 days) before TSH testing
Test Code
TSHR
CPT Codes
84443 (84439)
Includes
TSH; Free T4 added if TSH result abnormal
Preferred Specimen
SST Serum Separator
Minimum Volume
0.50 mL
Other Acceptable Specimens
Red No Gel
Transport Container
SST Serum Separator
Transport Temperature
Room Temperature
Specimen Stability
Refrigerated: 7 Days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Gross hemolysis
Methodology
Vitros 7600
Reference Range
0.47-4.68 mIU/L
Clinical Significance
The diagnosis of overt hypothyroidism by the finding of a low total T4 or free T4 concentration is readily confirmed by a raised TSH concentration. Measurement of low or undetectable TSH concentrations may assist the diagnosis of hyperthyroidism, where
concentrations of T4 and T3 are elevated and TSH secretion is suppressed. TSH tests with high levels of precision and
functional sensitivity claims of 0.01–0.02 mIU/L have been termed “third generation” tests. These have the advantage of
discriminating between the concentrations of TSH observed in thyrotoxicosis, compared with the low, but detectable,
concentrations that occur in subclinical hyperthyroidism.
concentrations of T4 and T3 are elevated and TSH secretion is suppressed. TSH tests with high levels of precision and
functional sensitivity claims of 0.01–0.02 mIU/L have been termed “third generation” tests. These have the advantage of
discriminating between the concentrations of TSH observed in thyrotoxicosis, compared with the low, but detectable,
concentrations that occur in subclinical hyperthyroidism.
Performed By
RFGH Laboratory
Performing Laboratory
RFGH Laboratory
