Nerve damage, also known as neuropathy, refers to conditions that result when nerves are damaged or diseased. This damage interrupts the signals between the brain and other parts of the body. Nerve damage can affect a single nerve, several nerves, or nerves across the body. There are over 100 different types of neuropathy. Some common symptoms include numbness, tingling, pain, weakness, and balance problems. Neuropathy is a relatively common condition that affects up to 20 million people in the United States.
Detecting nerve damage is important so that the underlying condition can be treated. This may help prevent the neuropathy from worsening and improve a person’s symptoms. Blood tests are one potential way to check for nerve damage. This article explores whether blood tests can in fact reliably detect nerve damage.
What causes nerve damage?
There are many potential causes of neuropathy, including:
– Diabetes – High blood sugar levels associated with diabetes can damage nerves over time. Diabetic neuropathy is the most common type of neuropathy.
– Autoimmune diseases – Conditions like lupus and rheumatoid arthritis cause the immune system to attack healthy cells, including nerves.
– Infections – Bacterial and viral infections, including HIV/AIDS, shingles, and hepatitis C can lead to inflamed and damaged nerves.
– Kidney disease – Waste buildup in kidney disease can damage nerves.
– Vitamin deficiencies – Lack of vitamins E, B1, B6, B12, and niacin can disrupt nerve function.
– Alcohol abuse – Long term excessive alcohol use can destroy nerve fibers.
– Chemotherapy – Cancer treatment drugs are toxic to nerves.
– Inherited disorders – Charcot-Marie-Tooth disease and other inherited neuropathies damage nerves over time.
– Repetitive stress – Activities like typing can compress nerves and eventually cause damage.
– Exposure to toxins – Heavy metals, industrial chemicals, and poisons can damage nerves.
– Trauma – Broken bones compressing nerves, surgery, or cuts that sever nerve fibers can lead to neuropathy.
– Tumors – Benign or cancerous growths can press on nerves.
– Unknown causes – Idiopathic neuropathy has no known cause.
How are nerve disorders conventionally diagnosed?
Doctors use a combination of approaches to determine if a person has nerve damage and identify the underlying cause:
– **Medical history** – The doctor will ask about symptoms, potential causes, and family history of neuropathy.
– **Physical exam** – The physician will test muscle strength, reflexes, and sensations to see if nerves are functioning normally.
– **Nerve conduction study** – Small electrodes on the skin measure how fast electrical signals move through a nerve. Slow conduction indicates nerve damage.
– **Electromyography** – A needle electrode inserted into the muscle evaluates muscle health at rest and during contraction. Abnormal signals suggest nerve or muscle dysfunction.
– **Quantitative sensory testing** – This determines the threshold at which various sensations like touch, vibration, heat, and cold are detected. Higher thresholds indicate possible neuropathy.
– **Tissue sample (biopsy)** – Removing and analyzing a small piece of nerve tissue can reveal nerve fiber damage.
– **Genetic testing** – Detects gene mutations that lead to inherited neuropathies.
– **Imaging tests** – MRIs, CT scans, ultrasounds, and X-rays help identify tumors, herniated discs, injuries, and other sources of nerve compression.
What types of blood tests detect nerve damage?
Certain substances in the blood can serve as markers indicating possible nerve injury. Some examples include:
– **Glucose** – Elevated blood sugar is associated with diabetic neuropathy. Fasting glucose or HbA1c blood tests detect diabetes or prediabetes.
– **Vitamin levels** – Low levels of vitamins B1, B6, B12, E and niacin can cause neuropathy. A vitamin panel checks for deficiencies.
– **Metabolic panel** – This looks at electrolyte and mineral levels and kidney function. Imbalances may contribute to neuropathy.
– **Liver enzymes** – Liver damage from hepatitis and other conditions can lead to nerve disorders. Liver enzyme tests like ALT, AST, and GGT measure liver health.
– **Inflammatory markers** – High erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) indicates inflammation that could be damaging nerves.
– **Thyroid hormones** – Uncontrolled hypothyroidism or hyperthyroidism alters metabolism and can affect nerves. Thyroid hormone levels show thyroid function.
– **Antibodies** – Antinuclear antibodies in lupus and rheumatoid factor in rheumatoid arthritis signify autoimmune activity against nerves.
– **Protein electrophoresis** – This distinguishes abnormal proteins in the blood, including antibodies that attack nerves.
– **Genetic tests** – Detect gene mutations for Charcot-Marie-Tooth disease and other inherited neuropathies.
Are blood tests sufficient to diagnose nerve damage?
Blood tests alone cannot conclusively diagnose nerve disorders. While they provide clues about possible causes of neuropathy, blood tests have limitations:
– They cannot confirm the presence of actual nerve damage or the extent and location of neurological deficits. The doctor still needs to perform a neurological exam.
– Some causes like trauma, tumors, and repetitive stress are not detected by blood tests. Imaging and other testing are required.
– Vitamin deficiency levels may be normal even when neuropathy is present. Deficiencies do not develop until late-stage.
– Kidney and liver function can appear normal in early stages of disease before neuropathy occurs.
– Inflammatory markers may not correlate with severity of autoimmune neuropathy symptoms.
– Diabetes can be ruled out with normal blood glucose, but other types of metabolic neuropathies may not have definitive blood markers.
– Genetic test results only indicate potential for inherited neuropathy. Further clinical evaluation is needed.
– There are no definitive blood biomarkers for idiopathic neuropathy with unknown causes.
When are blood tests used to assess nerve damage?
Doctors typically order blood tests for neuropathy evaluation in the following situations:
– To screen for diabetes, kidney disease, liver disorders, vitamin deficiencies, thyroid problems, autoimmune diseases, and paraproteinemia as potential causes of neuropathy.
– If family history suggests inherited neuropathy, genetic testing can identify mutations that confirm diagnosis.
– To establish baseline labs before initiating neuropathy treatment to monitor for side effects.
– To track progression of underlyingconditions like diabetes, kidney disease, or autoimmune disorders that could be worsening neuropathy.
– To monitor vitamin, mineral, and electrolyte levels during treatment to optimize neurological functioning.
– To identify deficiencies that require supplementation like vitamin B12 injections for pernicious anemia to prevent neuropathy progression.
– To measure inflammatory markers indicating active autoimmune disease that requires more aggressive treatment.
– To monitor for potential toxicity during chemotherapy that could exacerbate neuropathy.
What are the disadvantages of relying only on blood tests for neuropathy?
Exclusively using blood testing to evaluate nerve disorders has drawbacks including:
– Failure to detect structural causes like tumors, herniated discs, or injuries compressing nerves that require imaging.
– Inability to confirm presence and distribution of nerve deficits that require detailed neurological examination.
– Nerve conduction studies and electromyography are not performed, missing key data on nerve dysfunction.
– Normal blood tests may incorrectly rule out neuropathy, leading to missed diagnosis.
– Abnormal blood results might incorrectly suggest neuropathy without clinical correlation.
– Progression of nerve damage over time may be missed without repeat testing.
– Screening tests have limitations and may not reflect all vitamin deficiencies or toxicity.
– Lack of direct assessment of small fiber sensory polyneuropathy often associated with normal blood work.
– Over-reliance on blood tests can delay diagnosis and proper treatment.
Conclusion
Blood testing is a useful component of a comprehensive neuropathy evaluation. It can screen for common causes, establish baseline status, monitor conditions affecting nerves, guide genetic diagnosis, and assess risks of treatment. However, blood tests have limitations in both sensitivity and specificity for detecting and characterizing nerve disorders. They cannot substitute for a detailed medical history, physical examination, and more definitive tests like nerve conduction studies. Ultimately, blood tests must be interpreted in the full clinical context. While helpful indicators, they should not be solely relied upon to diagnose neuropathy in place of a complete neurological assessment.