Investigations - Blood Tests

Full Blood Count

This is a blood test that is often performed in people who have blacked out to make sure they do not have anaemia or bleeding as a cause or contributing factor to the blackout.

Electrolytes

This is a blood test that is often performed in people who have blacked out.
It ensures that the kidneys are working properly and can indicate if dehydration is present which may have contributed to a blackout.

If there is an abnormal build up of some of the substances in the blood such as potassium then an abnormal fast or slow heart beat may have occurred as the cause of the blackout.

Blood Sugar

This is a blood or finger prick test performed to look for evidence of a low blood sugar as a cause of a blackout.

A low blood sugar is a rare cause of a blackout except in diabetics who are taking tablets and insulin to lower the blood sugar.

Specialised Blood Tests

Other blood tests may be arranged if the history and examination suggest certain causes of a blackout.

• If there has been recent chest pain a blood test may be performed to look for evidence of heart muscle damage due to a heart artery blockage.
• Rarely blackouts are due to an abnormality of the gland system of the body and specialised testing is required to ensure that certain hormone levels, particularly the stress hormones, are normal

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