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This test promotes a cascade approach to more efficiently screen and evaluate a patient's functional thyroid status. TSH is used as the initial screening test because it provides the best indication of physiological thyroid hormone status. Increased TSH indicates inadequate levels of thyroid hormones, and a suppressed TSH indicates excess thyroid hormone activity.
No further testing will be performed if the initial TSA is within normal limits.
If the TSH concentration is >5.0 mIU/mL, a FT4 assay will be ordered to assess the likelihood and severity of potential hypothyroidism.
If the TSH is <0.3 mIU/mL, FT4 will also be automatically performed. The measurement of FT4 in the setting of low TSH allows for the more accurate assessment of potential hyperthyroidism. In cases where TSH is low and FT4 is <1.76 ng/dL, an additional FT3 assay will be performed to look for possible T3 thyrotoxicosis.
See individual test (TSH, FT4 and FT3) handbook entries.
* Reference ranges may change over time. Please refer to the original patient report when evaluating results.
Collect specimen in a red top or SST tube. Centrifuge, aliquot serum into a plastic vial and refrigerate up to 48 hours or freeze for longer storage. Specimen may be kept at room temperature for no more than 8 hours.