Fatigue after a brain injury - the 7 blood tests to ask for - Specialist Nutrition Rehab


24 Aug 2022

Fatigue after a brain injury — the 7 blood tests to ask for

Fatigue after brain injury


The fatigue that affects 20-80% of people after a brain injury (often called neuro-fatigue), is different from “ordinary” fatigue because it is often unrelated to levels of exertion and doesn’t improve even when someone rests.1, 2  The persistent nature of post-injury fatigue means it can negatively affect quality of life and pose a barrier to rehabilitation.1, 2, 3

Fatigue which occurs post-brain injury, may be caused by a multitude of factors – such as damage to the brain cells, sleep problems, medication side effects and depression.4  However, it is equally possible that one (or more) underlying medical issues are also contributing to the problem. Insufficient levels of certain vitamins and minerals, low thyroid function, high or low blood glucose levels, electrolyte imbalance and dehydration can all cause, or contribute to, feelings of fatigue.1  Speak to the GP to see if your client needs any of the following blood tests to rule out an underlying medical issue. While the assumption may be that these have been done at various times during the person’s treatment and recovery, dietitians frequently encounter clients where one or more of these tests have never been done. Annual blood tests are also recommended to monitor someone’s progress and detect any changes in vitamin/mineral levels.


1.  Full blood count

A full blood count provides information about the red blood cells, the white blood cells and platelets in the body. When it comes to fatigue, dietitians are usually most interested in a person’s haemoglobin levels. Iron is the main component of haemoglobin in red blood cells.  Without adequate iron, haemoglobin levels will be low and low haemoglobin levels means the cells will not be getting enough oxygen.  Fatigue can be one of the symptoms of this.


2.  Ferritin

Ferritin is the storage form of iron and reduced ferritin levels are an early sign that iron levels are becoming depleted.  If someone is not getting enough iron (or losing more than they should), the body will start using up these iron stores to try and keep haemoglobin levels within a normal range. C-reactive protein (which measures inflammation) should be checked at the same time, because ferritin levels are affected by inflammation — this will help interpret the results.5  Some people start to experience fatigue when their ferritin levels drop, even if their haemoglobin is still within the normal range.6  If left untreated, reduced ferritin levels will generally lead to reduced haemoglobin levels.


3. Vitamin B12 & folate

A deficiency of vitamin B12 and/or folate can affect red blood cells and lead to fatigue. Vitamin B12 deficiency can also damage the protective covering (myelin) on the peripheral nerves, and nerves of the spinal cord and brain, which can affect brain functioning, balance, memory and motor functioning.7  It can also cause numbness, pain and tingling in the hands and feet. Certain medications, such as proton pump inhibitors (e.g. omeprazole, lansoprazole), H2 receptor antagonists (e.g. ranitidine) and medication for type 2 diabetes (e.g. metformin), can increase the risk of vitamin B12 deficiency.7  Proton pump inhibitors and antiseizure medication (e.g. carbamazepine, sodium valproate) can also increase the risk of folate deficiency.8, 9


4.  Vitamin D

The symptoms of inadequate vitamin D levels include: fatigue, headache, musculoskeletal pain/weakness, depression and impaired cognitive performance.10  However, the main concern with inadequate vitamin D is the risk to bone health. After a traumatic brain injury, 80.2% of people were diagnosed with vitamin D levels that were either insufficient or deficient (<70 nmol/L) and these inadequate levels of vitamin D were associated with worse brain functioning and more severe depression.11

Vitamin D is produced when skin is exposed directly to sunlight.  However, in the UK (and other northern countries), it is only possible to produce sufficient amounts of vitamin D from the sun between late-March and September, and even that is dependent on time of day, cloud cover, clothing and sunscreen use.  People who are hospitalised, in rehabilitation and/or in a care facility, often spend most of their time indoors away from the sun. Combine all of this with the fact that very few foods contain substantial amounts of vitamin D (oily fish is the main source), and the fact that certain antiseizure medications (e.g. carbamazepine, phenytoin) actively break down vitamin D in the body and it’s no wonder so many people are deficient after a major trauma/injury.12

Click here for more information on vitamin D deficiency and when to take supplements.


5.  Thyroid function

Thyroid hormones regulate the body’s metabolism. If one or more of these hormones is low, a person can feel fatigued and/or have low mood and impaired cognitive functioning.13, 14  People with a brain injury need a more extensive set of thyroid tests than the general population. Both thyroid hormones, triiodothyronine (T3) and thyroxine (T4), need to be checked in addition to thyroid-stimulating hormone (TSH). Normally, TSH causes the body to produce T4 and then T4 is converted to the “active” form which is T3. However, due to various problems with the hypothalamus, pituitary gland and thyroid glands after a brain injury, this process doesn’t always happen like it should. T3 levels were found to be reduced in 66.7% of patients with brain injuries, and T4 levels were low in 22%.15  This won’t be picked up if only TSH is checked.


6.  Blood glucose levels

Blood glucose is used by the cells to produce energy. Blood glucose levels which are too high (because the glucose can’t move from the blood into the cell) or too low (because there is a miss-match between food intake and insulin levels) can both cause feelings of fatigue.16


7.  Urea & electrolytes

The body requires sufficient amounts of fluid and electrolytes such as sodium, potassium and magnesium (among others) in order to function properly. Dehydration, or having electrolytes which are too low (due to loose stools, vomiting or other reasons), can contribute to fatigue.1   Magnesium and phosphate are not included in the general test for “electrolytes.”  These blood tests will need to be requested separately, if someone’s food intake is exceptionally low in these nutrients and/or the person has digestive issues which reduce absorption or increase losses of magnesium or phosphate.


Acting on the results

Any deficiencies identified by the above blood tests need to be managed by the GP and corrected with prescription strength supplements. Standard over-the-counter multivitamin and mineral supplements are generally not strong enough to correct deficiencies. After the course of treatment, be sure to ask for another blood test to ensure the deficiency has been corrected and ask if anything can be done to prevent the deficiency from happening again in the future (e.g. changes to diet or medication).

Dietitians will often request the blood tests outlined above and can also provide practical support and advice to ensure someone’s diet contains sufficient levels of vitamins, minerals, electrolytes and fluid.  Dietitians can also help manage gut problems (which will affect electrolyte balance) and give advice on managing blood glucose levels.

For more information or to refer a client with a brain injury for a dietetic assessment, contact info@specialistnutritionrehab.co.uk or 0121 384 7087.

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West Midlands
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0121 384 7087

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