Adrenoleukodystrophy (ALD) is a rare inherited condition in which the breakdown of very long-chain fatty acids (VLCFA) is hindered. The resulting accumulation of VLCFA in the blood and body tissues, especially in the brain and spinal cord, causes the symptoms associated with ALD. The build-up of VLCFA in the adrenal glands can impair their function, causing adrenal insufficiency also known as Addison’s disease.
Blood tests are used to check for elevated levels of VLCFA once a doctor suspects ALD, based on the patient’s symptoms. Blood tests are minimally invasive and often the first diagnostic test used to detect ALD. Adrenal insufficiency can also be determined by testing for adrenal hormone (cortisol and aldosterone) levels in the blood.
Blood tests for VLCFA levels
A blood sample collected after overnight fasting is preferred for the detection of VLCFA levels, which are then determined using a combination of two advanced bioanalytical techniques — liquid chromatography (LC) and mass spectrometry (MS).
VLCFAs in blood are first separated by LC based on their weight and then identified by MS on the basis of their molecular structure. Fatty acids are made of carbon, hydrogen, and oxygen atoms. In VLCFA, there are more than 18 carbon atoms (C18). For ALD diagnosis, VLCFA types with C26, C22, and C24 are of importance. An increased C26, and elevated ratio of C26: C22 and C24: C22 is considered a positive sign for ALD.
Although reliable, VLCFA blood test results may vary especially in ALD-carrier females. Therefore, a VLCFA blood test is often followed by genetic testing which can be performed using the same blood sample.
Blood tests for Addison’s disease
Cortisol levels in the blood are used to diagnose Addison’s disease. The concentration of cortisol in the blood is different throughout the day, with a peak in the morning. Therefore, for this test, blood samples are collected early in the morning, and overnight fasting may be required. Very low levels of cortisol in the blood is an indication of adrenal insufficiency.
Furthermore, electrolyte imbalance occurs in adrenal insufficiency. Measuring blood levels of electrolytes such as sodium and potassium may be helpful because low sodium and high potassium levels, along with low cortisol levels, are characteristic of adrenal insufficiency.
Doctors may recommend an adrenocorticotropic hormone (ACTH) stimulation test to confirm adrenal gland dysfunction. ACTH is a hormone produced by the pituitary gland, which is situated at the base of the brain. It stimulates the adrenal gland to produce cortisol and aldosterone. If the adrenal glands are damaged due to VLCFA build-up, ACTH stimulation will have minimal effect, which can be detected by measuring the cortisol levels in blood before and after an injection of synthetic ACTH.
Aldosterone levels are also measured in blood samples, and low levels indicate Addison’s disease.
In addition, blood tests can help monitor the impact of hormone replacement therapy on Addison’s disease.
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