What laboratory investigations are essential for confirming myxoedema coma in an emergency situation?

Essential laboratory investigations to confirm myxoedema coma in an emergency include:

• Measurement of thyroid function tests, specifically thyroid-stimulating hormone (TSH) and free thyroxine (FT4), to confirm severe hypothyroidism. Typically, TSH will be elevated and FT4 markedly low in primary hypothyroidism leading to myxoedema coma.
• Assessment of other biochemical parameters such as serum electrolytes, glucose, and cortisol to evaluate for associated metabolic disturbances and adrenal insufficiency, which can coexist and worsen the clinical picture.
• Additional tests may include arterial blood gases to assess respiratory function and acid-base status, as respiratory depression is common in myxoedema coma.

In emergency settings, rapid measurement of TSH and FT4 is critical to confirm the diagnosis and guide urgent thyroid hormone replacement therapy.

Note: The NICE guideline NG145 on thyroid disease management emphasizes measuring TSH and FT4 when thyroid dysfunction is suspected, with TSH above the reference range and low FT4 confirming hypothyroidism ¹. Although the guideline does not explicitly detail myxoedema coma investigations, the principle of confirming severe hypothyroidism via TSH and FT4 applies in this emergency context.