Blood tests are used to look for evidence of diseases, the symptoms of which are similar to those of ALS. They can help, therefore, to exclude ALS. The following blood tests may be performed.
Thyroid function tests
The thyroid is an endocrine (hormone-secreting) gland that releases thyroid hormones. These hormones control energy metabolism and other processes in the body. The term thyroid disease is usually used to describe an under-active thyroid gland. When the thyroid is under-active, blood levels of the thyroid hormone thyroxine (or T4) are too low. To compensate for the decreased activity of the thyroid, another gland called the pituitary gland, releases the so-called thyroid stimulating hormone (TSH). For this reason, TSH levels in the blood are high when the thyroid is under-active. Thyroid hormone levels also can be measured in the urine, but this is less common.
Both, an under-active and hyperactive thyroid can cause myopathy (muscle disease). Some symptoms of myopathy, such as muscle weakness and cramps, also can be seen in ALS.
Parathyroid disease test
The parathyroid also is a gland and the hyperactivity of this gland is usually caused by a tumor. The parathyroid gland then produces high levels of the parathyroid hormone, which can be measured in the blood. Because the parathyroid hormone controls calcium in the blood, calcium levels are increased as well.
A hyperactive parathyroid also can affect muscle function and lead to symptoms such as muscle weakness, cramps, and twitching, which also occur in ALS patients.
Vitamin B12 deficiency test
Vitamin B12 is needed for the formation of new red blood cells, for neurological function, and for DNA synthesis. The levels of vitamin B12 can be measured with a blood test.
Vitamin B12 deficiency also can affect motor neurons or those controlling muscles, leading to symptoms that can resemble ALS.
The human immunodeficiency virus (HIV) attacks the white blood cells that are part of the immune system and can cause acquired immunodeficiency syndrome (AIDS). HIV is diagnosed by testing the blood or saliva for antibodies against the virus.
Nerve damage is common in HIV patients and can be caused by the virus itself, the medication used to treat the disease, or infections that occur as a consequence of the suppressed immune system. When motor neurons are affected, this can lead to symptoms that also are seen in ALS patients, such as muscle weakness.
Hepatitis is a condition in which the liver is inflamed. It usually is caused by hepatitis viruses, but can also be caused by other infections, toxic substances, or autoimmune diseases. Hepatitis diagnosis involves measuring markers in the blood that provide information about liver function.
Albumin is a protein produced by the liver, and low levels of this protein are a sign of liver disease. The liver enzymes ALP, ALT, and AST are elevated in liver disease. These can be detected in the blood.
In addition, increased bilirubin levels are a sign of liver disease. Bilirubin is a pigment that is created when red blood cells are broken down. Usually, bilirubin is passed on to the liver and excreted together with bile. If the liver does not function correctly, bilirubin levels in the blood rise.
Hepatitis viruses do not infect nerve or muscle cells, but muscle damage is seen in hepatitis-infected patients. This is thought to be caused by an immune response that is triggered by the virus. The muscle damage can cause symptoms that are similar to the symptoms of ALS.
Autoimmune disease tests
The immune system functions to protect the body against harmful foreign substances such as bacteria, parasites, and viruses. In an autoimmune disorder, the body mistakenly produces antibodies against its own cells and tissues. One way to diagnose an autoimmune disease is by measuring inflammation markers and autoantibodies in the blood.
There are autoimmune disorders where the immune system specifically attacks nerve cells. For example, multifocal motor neuropathy is an autoimmune disease that affects only motor neurons. Muscle weakness, cramps, and twitching are common symptoms and resemble the symptoms of ALS.
Creatinine kinase test
Creatinine kinase is an enzyme that is mainly found in the heart, brain, and skeletal muscles. Increased levels of creatinine kinase in the blood are a sign of muscle damage. Muscle damage can be caused by strenuous exercise, but also by muscle disease. Creatinine kinase levels also can be elevated in ALS patients.
Cancer blood test
Cancer is the abnormal proliferation of cells within the body. There are more than 100 different types of cancer, which can cause a wide variety of symptoms.
Cancer can affect muscle function in different ways and cause symptoms that are similar to those of ALS. For example, a tumor may mechanically compress a motor neuron and cause muscle weakness. Cancer can also alter the immune response, and cause immune cells to target and damage muscle tissue, again leading to ALS-like symptoms. Finally, tumors can occur in nerve cells themselves and interfere with neuronal function.
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