A 64 year old woman consulted her medical practitioner about her general lassitude
• Included weight gain
• Episodes of constipation
• A blood specimen was taken for thyroid function tests.
- Both the tT4 and fT4 are less than the reference range, but since the patient’s own reference interval is unknown; a biochemical diagnosis cannot be made from these results alone.
- Serum TSH secretion provides a direct indicator in the individual patient of the bioavailability of circulating thyroid hormone
- The TSH concentration in the above case in markedly raised
- The high TSH is therefore diagnostic of primary hypothyroidism
- TSH value greater than twice the upper limit of the reference interval is a biochemical definition of primary hypothyroidism.