Thyroid Function Tests – TFT/TSH
Code:
TSH
Sample Type:
Serum (Gold Top)
Minimum volume: 1 mL
Ref Ranges/Units:
Adults – TSH: 0.3 – 4.50 mIU/L
Results >50 mIU/L will be phoned to the requesting clinician.
Turnaround:
Same Day (60 minutes from receipt for Urgent Samples).
Stability:
8 days at 20‑25°C
14 days at 2‑8°C
24 months at ‑20°C
Freeze only once
Special Precautions/Comments:
Please indicate on request form if patient is on any thyroid treatment.
Additional Information:
Thyroid functions tests are used as the first line investigation of hypothyroidism and hyperthyroidism. Thyroid stimulating hormone (TSH) is measured in the first instance. Thyroid hormones, free T4 (thyroxine) and/or free T3 (triiodothyronine), may be added if TSH is abnormal.
An increased TSH with low free T4 is indicative of thyroid insufficiency (primary hypothyroidism). A low free T4 with a low TSH is suggestive of secondary or tertiary hypothyroidism. In contrast, increased free T4 with a suppressed TSH is indicative of thyroid overactivity (hyperthyroidism). A normal free T4 in the presence of an abnormal TSH is suggestive of subclinical (‘borderline’) thyroid dysfunction. Non-thyroidal illness can cause transiently abnormal thyroid function tests.
Measurement of TSH is also used to monitor thyroid hormone replacement in hypothyroidism. TSH in the normal range is the therapeutic target. A high TSH may indicate undertreatment or non-compliance whereas a low TSH suggests overtreatment.
South of Tyne & Wear Pathology Centre
