Blood tests during an ALS evaluation
Reviewed by Amyotrophic lateral sclerosis (ALS) can be challenging to diagnose because its symptoms often overlap with those of other conditions.
Blood tests for ALS are an important part of the diagnostic evaluation. They can help doctors identify or rule out other conditions that might be causing symptoms.
There is currently no routine ALS blood test that can confirm or rule out the disease on its own. Instead, physicians evaluate blood tests during ALS diagnosis alongside clinical symptoms, physical examinations, and other specialized diagnostic assessments.
Can a blood test diagnose ALS?
Blood tests cannot diagnose or rule out ALS on their own. An ALS diagnosis is based on progressive motor impairment, objective evidence of motor neuron dysfunction, and careful investigations to exclude other illnesses that could explain symptoms.
Researchers are studying blood biomarkers that could speed up diagnosis and make it more objective. For now, however, these biomarkers complement rather than replace a comprehensive neurological workup.
Does everyone receive the same blood tests?
There is no universal blood panel for ALS. Standard workups typically evaluate blood cell counts, electrolytes, kidney and liver function, thyroid health, vitamin deficiencies, and markers of muscle injury.
More specialized blood tests for ALS mimics may be ordered when an individual’s specific symptoms or personal medical history point toward a particular condition.
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| Test category | Examples | What doctors may be investigating | Limitation |
|---|---|---|---|
| Blood chemistry and hematology tests | Complete blood count, comprehensive metabolic panel | Metabolic or systemic illness | An abnormality may not explain neurological symptoms |
| Endocrine and nutritional tests | TSH, T4, vitamin B12, folate, calcium | Thyroid, nutritional, or metabolic disorders | Abnormal results may require additional testing |
| Muscle tests | Creatine kinase (CK) | Muscle injury or muscle disease | CK can also be elevated in ALS |
| Infectious disease tests | HIV, Lyme disease, syphilis | Infections that can cause neurological symptoms | Testing is generally based on risk or exposure |
| Immune and protein tests | Protein electrophoresis, disease-specific antibodies | Immune-mediated neuropathies and other disorders | No single immune or protein test can diagnose or rule out ALS |
Which routine blood tests may be ordered?
A healthcare professional may order one or several blood tests based on a patient’s symptoms, medical history, and physical examination. Routine tests help identify other potential causes of motor symptoms, such as muscle weakness. Doctors then consider targeted tests when a patient’s clinical picture suggests an alternative disorder.
Complete blood count and metabolic testing
A complete blood count measures different types of blood cells. A comprehensive metabolic panel measures electrolytes as well as kidney and liver function.
These tests can identify abnormalities that may explain weakness or other symptoms and help determine if certain medications are appropriate to take based on a patient’s liver health.
Thyroid function tests
The thyroid is a gland that releases hormones controlling energy metabolism and other vital bodily processes.
Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can cause muscle weakness, cramps, or fatigue that resemble early ALS symptoms.
Vitamin B12, folate, and other nutritional tests
Doctors routinely check vitamin B12 and folate levels because these nutrients are essential for healthy nerve function and red blood cell production.
Nutritional deficiencies can cause significant neurological problems, including weakness, numbness, and balance difficulties. A doctor may order other nutritional assays if a person’s symptoms or history suggest a particular deficiency.
Creatine kinase and muscle-enzyme testing
Creatine kinase (CK) is an enzyme found primarily in skeletal muscle, heart muscle, and the brain. When muscle cells are damaged, CK can enter the bloodstream.
CK is measured to check for underlying muscle diseases. However, an abnormal CK level does not confirm or rule out ALS or an alternative diagnosis.
Calcium, magnesium, and parathyroid-related testing
Electrolyte imbalances involving calcium or magnesium can disrupt nerve and muscle signaling. These imbalances can trigger muscle twitches and cramps that closely mimic ALS symptoms, making calcium testing typically part of an ALS evaluation.
Parathyroid hormone (PTH), which regulates calcium levels in the body, may also be measured. Doctors evaluate calcium and PTH results together to determine if an endocrine issue is affecting muscles.
What specialized blood tests may be ordered?
Infectious disease testing
Certain infections can cause neurological symptoms that may resemble aspects of ALS.
Depending on the person’s symptoms, history, and geographic exposure, doctors may include tests for Lyme disease, HIV, or syphilis. These are targeted tests, not a mandatory infectious disease panel for everyone undergoing an ALS evaluation.
Autoimmune and inflammatory testing
In an autoimmune disorder, the immune system mistakenly produces antibodies that attack the body’s own healthy tissues.
Some immune disorders cause progressive muscle weakness. One notable mimic of ALS is multifocal motor neuropathy, an immune-mediated disorder that impairs motor nerves. If an autoimmune condition is suspected, doctors may test for general inflammatory markers or disease-specific autoantibodies.
Protein, antibody, and paraneoplastic testing
Serum protein electrophoresis and immunofixation tests detect abnormal protein patterns in the blood that may indicate blood or bone marrow disorders.
Other antibody tests help identify specific neuromuscular conditions. For example, acetylcholine receptor and MuSK antibody tests can help diagnose myasthenia gravis.
In rare instances, certain cancers trigger an immune response that mimics ALS, so paraneoplastic testing may be considered when features such as unusually rapid progression, nonmotor neurological symptoms, abnormal blood findings, or other clinical signs raise suspicion of a cancer-associated neurological syndrome.
Heavy-metal or other exposure testing
Exposure to environmental or industrial toxins, including lead, arsenic, or mercury, can damage motor nerves and cause muscle weakness. Doctors may order heavy metal screening if a patient’s work environment or living conditions involve potential exposure.
How should I prepare for blood tests?
Most blood tests require little preparation, but individuals should always ask their healthcare team if they need to fast beforehand. A person receiving blood tests should not stop or change current medication unless instructed to do so by the healthcare provider.
Before testing, be sure to tell the care team about:
- Prescription and over-the-counter medications
- Vitamins and herbal supplements
- Recent illnesses or infections
- Pregnancy
- Relevant workplace or environmental chemical exposure
Intense physical exercise and alcohol consumption shortly before a blood draw can temporarily alter certain lab results, particularly CK levels.
What do abnormal blood test results mean?
An abnormal result does not necessarily mean doctors have found the cause of a patient’s symptoms.
When a result may identify a treatable condition
Sometimes a blood test identifies a treatable condition. Doctors can then determine whether that condition adequately explains the symptoms and if further neurological evaluation is needed.
When an abnormality may be incidental
An abnormal blood test also does not necessarily exclude ALS. The doctor will interpret the blood test result in the context of a patient’s symptoms, examination, and other test results.
When repeat or confirmatory testing is needed
Borderline, unexpected, or fluctuating results often require repeat draws or more specialized confirmatory tests before a person’s care team draws firm conclusions.
What do normal blood test results mean?
Normal blood test results help rule out many alternative explanations for symptoms, such as metabolic diseases, infections, and common vitamin deficiencies. However, normal blood tests do not confirm an ALS diagnosis.
Doctors must still combine these findings with a patient’s symptom history, physical examinations, and other diagnostic procedures to determine whether ALS or another condition best explains the clinical picture.
Are there blood biomarkers for ALS?
Neurofilament and other biomarkers under study
One of the most extensively studied ALS biomarkers is neurofilament light chain (NfL). Neurofilaments are internal structural proteins found inside nerve cells. When motor neurons are injured or break down, NfL is released into the cerebrospinal fluid and bloodstream.
A 2025 systematic review and meta-analysis of 9,078 participants found that NfL had the highest diagnostic accuracy among the blood and cerebrospinal fluid biomarkers evaluated. Researchers are also investigating combinations of proteins and other biomarkers that may help distinguish ALS from other neurological conditions in the early phase of the disease.
Why research biomarkers are not stand-alone diagnostic tests
Promising research does not mean a single biomarker test can replace a neurologist’s comprehensive evaluation.
For instance, elevated NfL levels indicate active nerve damage, but they are not specific to ALS. It can rise in other neurodegenerative conditions, head trauma, and multiple sclerosis. While NfL is a valuable tool for tracking disease activity and prognosis, it cannot be used alone to establish a definitive diagnosis.
How do blood tests fit with other diagnostic tests?
Blood tests represent just one component of a complete diagnostic workup. Other crucial evaluations include electromyography, nerve conduction studies, and magnetic resonance imaging of the brain and spinal cord.
In selected cases, a lumbar puncture (spinal tap) may be performed to analyze cerebrospinal fluid for signs of inflammation, infection, or unusual protein levels.
Establishing an accurate diagnosis requires documented evidence of progressive motor impairment and motor neuron degeneration, paired with objective tests that rule out mimic diseases.
Questions to ask about blood test results
When discussing laboratory tests for ALS with their healthcare team, a person may want to ask:
- Which results were abnormal, and could any of them explain my symptoms?
- Do I need repeat testing or additional confirmatory labs?
- Were these tests intended to rule out specific conditions that mimic ALS?
- Are more specialized blood panels warranted based on my symptoms or medical history?
- What additional neurological assessments do I need next?
- Would a biomarker test, such as an NfL blood draw, provide useful information in my situation?
ALS News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
