Tired all the time? The blood tests that find the usual causes

Feeling tired all the time is one of the most common reasons people see a doctor. Often there is a simple explanation, such as poor sleep or stress. But some common, treatable causes only show up on a blood test.

The blood tests worth doing first

Iron and ferritin

Ferritin shows how much iron your body has stored. Low iron stores can make you tired, breathless and less able to concentrate, even before you become anaemic. It is especially common in women with heavy periods, during and after pregnancy, and in people who eat little red meat.

Full blood count

This checks for anaemia (low haemoglobin) and gives clues to its cause. It also looks at your white cells and platelets.

Vitamin B12 and folate

Low B12 or folate can cause tiredness, and low B12 can also cause pins and needles or memory problems. B12 is more likely to be low in vegans, older adults and people taking some medicines, such as metformin or long-term acid reducers.

Thyroid

An underactive thyroid can cause tiredness, weight gain, feeling cold and low mood. TSH is the main test, often with free T4.

Vitamin D

Low vitamin D is common in the UK, particularly in winter and in people who spend little time outdoors. It can contribute to tiredness and aches.

Blood sugar, kidneys and liver

HbA1c checks for diabetes, which can make you feel tired and thirsty. Kidney and liver tests look for other, less common causes.

Which test should I choose?

If tiredness is your main concern, a broad check usually makes most sense, because the cause isn't always the one you expect. Our Full Body Health Check covers all of the markers above in one blood test. If you only want to check your iron and B12, our Iron and B12 checks are a smaller option.

What a blood test won't find

Many causes of tiredness don't show up on a blood test, including poor sleep, sleep apnoea, stress, low mood, anxiety, long working hours and some medicines. A normal result is useful because it rules out common physical causes, but it doesn't mean your tiredness isn't real.

What happens with your results

A GMC-registered doctor reviews every result before you see it and explains what it means for you. If something needs treatment or follow-up, a doctor contacts you directly.