| . | Low TSH . | Normal TSH . | High TSH . |
|---|---|---|---|
| High FT4 | Overt hyperthyroidism (0.1–0.5%) • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Thyroiditis | High FT4, Normal TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance | High FT4, high TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance |
| Normal FT4 | Subclinical hyperthyroidism (1–4%) • Physiological • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Molar pregnancy | Normal thyroid function (85–95%) | Subclinical hypothyroidism (2–5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine |
| Low FT4 | Low FT4, low TSH (rare) • Non-thyroidal illness • Central hypothyroidism • Assay interference | Hypothyroxinaemia (2.5%) • Iodine deficiency • Assay problems • Idiopathic | Overt hypothyroidism (0.2–0.5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine • Iodine deficiency |
| . | Low TSH . | Normal TSH . | High TSH . |
|---|---|---|---|
| High FT4 | Overt hyperthyroidism (0.1–0.5%) • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Thyroiditis | High FT4, Normal TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance | High FT4, high TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance |
| Normal FT4 | Subclinical hyperthyroidism (1–4%) • Physiological • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Molar pregnancy | Normal thyroid function (85–95%) | Subclinical hypothyroidism (2–5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine |
| Low FT4 | Low FT4, low TSH (rare) • Non-thyroidal illness • Central hypothyroidism • Assay interference | Hypothyroxinaemia (2.5%) • Iodine deficiency • Assay problems • Idiopathic | Overt hypothyroidism (0.2–0.5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine • Iodine deficiency |
Prevalence in brackets are estimates from literature.1,8–10 Definitions of thyroid dysfunction should be based on trimester-specific, population-specific and assay-specific reference ranges for FT4 and TSH.7
| . | Low TSH . | Normal TSH . | High TSH . |
|---|---|---|---|
| High FT4 | Overt hyperthyroidism (0.1–0.5%) • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Thyroiditis | High FT4, Normal TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance | High FT4, high TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance |
| Normal FT4 | Subclinical hyperthyroidism (1–4%) • Physiological • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Molar pregnancy | Normal thyroid function (85–95%) | Subclinical hypothyroidism (2–5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine |
| Low FT4 | Low FT4, low TSH (rare) • Non-thyroidal illness • Central hypothyroidism • Assay interference | Hypothyroxinaemia (2.5%) • Iodine deficiency • Assay problems • Idiopathic | Overt hypothyroidism (0.2–0.5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine • Iodine deficiency |
| . | Low TSH . | Normal TSH . | High TSH . |
|---|---|---|---|
| High FT4 | Overt hyperthyroidism (0.1–0.5%) • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Thyroiditis | High FT4, Normal TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance | High FT4, high TSH (rare) • Assay interference • TSH secreting adenoma • Thyroid hormone resistance |
| Normal FT4 | Subclinical hyperthyroidism (1–4%) • Physiological • Gestational transient thyrotoxicosis • Graves’ disease • Toxic nodular goitre • Molar pregnancy | Normal thyroid function (85–95%) | Subclinical hypothyroidism (2–5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine |
| Low FT4 | Low FT4, low TSH (rare) • Non-thyroidal illness • Central hypothyroidism • Assay interference | Hypothyroxinaemia (2.5%) • Iodine deficiency • Assay problems • Idiopathic | Overt hypothyroidism (0.2–0.5%) • Hashimoto’s thyroiditis • Post-surgical • Post-radioiodine • Iodine deficiency |
Prevalence in brackets are estimates from literature.1,8–10 Definitions of thyroid dysfunction should be based on trimester-specific, population-specific and assay-specific reference ranges for FT4 and TSH.7
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