Question

I’ve been feeling generally unwell and more fatigued – mentally and physically, for the past few months.
My GP ordered some routine blood tests – all of which were normal apart from having a slightly lower than normal level of sodium in the blood. My GP isn’t too concerned and is going to repeat the blood test. Could a low sodium level be caused by having ME?

Answer

The level of sodium in the blood has to be well controlled because having a level that is too low or too high can both cause problems.

Having a low level of blood sodium is known as hyponatraemia. This is defined as having a blood test result of less than 135 mmol/litre. Mild hyponatraemia is normally defined as 125 – 135 mmol/litre and moderate hyponatraemia is 115-125 mmol/litre. Severe hyponatraemia, which requires urgent medical attention, is defined as less than 115 mmol/litre.

Having a low blood sodium level can cause a number of symptoms – some of which also occur in ME/ CFS. Common ones include:

• Cognitive dysfunction and fatigue – including memory problems and difficulty concentrating
• General fatigue
• Headaches
• Muscle cramps and weakness

Untreated hyponatraemia can also lead to walking abnormalities and weaker bone structure with a risk of falls and fractures. Chronic or more severe hyponatraemia can cause serious neurological problems – including seizures.

To go back to your question: ME/CFS does not cause a drop in sodium levels. However, there are a number of medical conditions and drugs that cause low sodium levels. Some of these medical conditions also cause fatigue and ME/CFS-like symptoms. So these conditions should always be considered if someone with ME/CFS has a low sodium level.

• Medical conditions and drugs that can cause low sodium levels include:
• Diuretic (water-losing) drugs, ACE inhibitors (for high blood pressure) and SSRIs (antidepressants)
• Drinking too much water Diarrhoea and/or vomiting
• Kidney and liver disease
• Addison’s disease (low levels of cortisol)
• Hypothyroidism (low thyroid function)

So, someone has a persistently low level of sodium in the blood, this is what your GP should do. It’s important to take a full clinical history, do a physical examination and check liver, kidney and thyroid gland function, adrenal gland function (with an 8am cortisol level test) and blood markers for infection.