Anaemia

A full blood count shows whether your haemoglobin is low. Anaemia is one of the most common physical causes of fatigue, especially in women with heavy periods.

Thyroid

An underactive thyroid slows everything down: tiredness, weight gain, feeling cold, constipation and low mood. A thyroid function test checks TSH, free T4 and free T3.

Vitamin D

Low vitamin D is common in UK winters and can cause aches and fatigue. A vitamin D test shows whether you need a supplement.

Blood sugar

Undiagnosed diabetes can cause tiredness, thirst and needing to pass urine more often. An HbA1c test checks for it.

A broader check

A Well Person Profile combines blood count, diabetes, kidney and liver checks in one sample.

When to see your GP

See your GP if tiredness has lasted several weeks without an obvious cause, or comes with weight loss you can’t explain, breathlessness, night sweats or a new lump.

Please note: this guide is general information and doesn’t replace advice from your GP. If you feel very unwell, call NHS 111, or 999 in an emergency.

Tests mentioned in this guide

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