How to interpret Thyroid function tests
| TSH | T4 | T3 | Most likely interpretation |
| Undetectable | Raised | Raised | Primary thyrotoxicosis |
| Undetectable or low | Raised | Normal | Overtreatment of hypothyroidism with levothyroxine
FACTITIOUS THYROTOXICOSIS |
| Undetectable | Normal | Raised | Primary T3 toxicosis |
| Undetectable | Normal | Normal | Subclinical thyrotoxicosis |
| Undetectable or low | Raised | Low or normal | Non-thyroidal illness
Amiodarone therapy |
| Undetectable or low | Low | Raised | Overtreatment of hypothyroidism with liothyronine (T3) |
| Undetectable | Low | Low | Secondary hypothyroidsm
Transient thyroiditis in evolution |
| Normal | Low | Low | Secondary hypothyroidsm |
| Mildly elevated (5-20 mIU/L) | Low | Low | Primary hypothyroidsm
Secondary hypothyroidsm |
| Elevated >20 mIU/L | Low | Low | Primary hypothyroidsm |
| Mildly elevated (5-20 mIU/L) | Normal | Normal | Subclinical hypothyroidism |
| Elevated 20-500 mIU/L | Normal | Normal | Artefact
Heterophilic antibodies |
| Elevated | Raised | Raised | Non-adherence to levothyroxine replacement-recent loading dose
Secondary thyrotoxicosis Thyroid hormone resistance |
