THYROID STIMULATING HORMONE (TSH) - (P)
Test Code: TSH
Test Indications: TSH is used for the detection of thyroid dysfunction or the monitoring of patients with thyroid disease.
Recommendations: Determination of TSH level is the initial test used in the assessment of thyroid function. Very slight changes in circulating free T4 and free T3 levels result in much greater opposite changes in TSH level. Therefore, it is a very sensitive and specific marker for assessing thyroid disorders in patients with an intact pituitary-thyroid axis. If TSH is normal, no additional testing is necessary. When TSH is abnormal, appropriate follow-up testing is automatically performed to identify the nature of the thyroid disorder (subclinical or overt hypo- or hyperthyroidism).
Abnormal TSH will reflex to the addition of free T4 and free T3 as follows:
Free T4 will be performed when TSH < 0.40 mU/L or ≥ 4.3 mU/L
Free T3 will be performed when TSH < 0.09 mU/L
Patient Preparation Instructions: This test is unaffected by multivitamins (45–125 µg biotin) or biotin-only supplements.
For additional information see:
Plasma: 2.0 mL
Stability 14 days refrigerated, 2 years frozen
Serum: 2.0 mL
Samples must be transferred to an aliquot tube and stored frozen if analysis will not be complete within 48 hours (#110-10-05 Serum / Plasma Separation Procedure & Transport)