From the Guidelines
For a patient presenting with neuropathy, I recommend ordering a comprehensive panel of laboratory tests to identify the underlying cause, including HbA1c, vitamin B12, TSH, vitamin B6, folate, serum protein electrophoresis, and immunofixation, as suggested by the most recent guideline update 1. These tests should be considered to identify common causes of neuropathy such as diabetes, vitamin deficiencies, thyroid dysfunction, autoimmune conditions, infections, and toxin exposures.
- Additional important tests may include erythrocyte sedimentation rate, C-reactive protein, antinuclear antibody, rheumatoid factor, hepatitis B and C serologies, HIV testing, and vitamin B6 levels.
- For suspected inflammatory neuropathies, consider anti-ganglioside antibodies and anti-MAG antibodies, as well as other tests guided by the neuropathy phenotype, such as ANA, ESR, CRP, ANCA, anti–smooth muscle, SSA/SSB, RNP, anti-dsDNA, ganglioside ab, anti-Hu (ANNA-1 ab), thiamine, Lyme, hepatitis B or C, and HIV 1.
- Heavy metal screening (lead, mercury, arsenic) may be appropriate with relevant exposure history. The results of these laboratory investigations will guide appropriate treatment, which is essential since addressing the underlying cause can potentially halt progression or even reverse neuropathic symptoms in some cases, ultimately improving morbidity, mortality, and quality of life.
- Early diagnosis through these laboratory investigations is crucial for optimal management and preventing further nerve damage, as emphasized in recent standards of care in diabetes 1.
From the Research
Laboratory Tests for Neuropathy
To diagnose and manage neuropathy, several laboratory tests can be ordered. The choice of tests depends on the clinical presentation and suspected underlying cause of neuropathy.
- Electrophysiological tests such as nerve conduction studies (NCS) and quantitative sensory testing (QST) can be used to evaluate neuropathy 2.
- Blood tests, including glucose tolerance test, glycosylated hemoglobin (HbA1c), vitamin B12 levels, and thyroid function tests, can help identify underlying causes of neuropathy 2, 3.
- Genetic testing, including comprehensive multigene panel testing, can be used to diagnose hereditary neuropathies 4.
- Imaging studies, such as magnetic resonance imaging (MRI) of the brain or spine, may be ordered in some cases, although their yield may be low 3.
- Other tests, such as autonomic function tests, CSF examination, and nerve and muscle biopsy, may be necessary in certain cases 2, 5.
Specific Tests
Some specific tests that may be ordered for patients with neuropathy include:
- HbA1c to assess glucose control 2
- Vitamin B12 levels to rule out deficiency 2
- Thyroid function tests to evaluate for thyroid dysfunction 2
- Glucose tolerance test to diagnose impaired glucose tolerance or diabetes 3
- NCS and QST to evaluate nerve function 2
- Genetic testing for hereditary neuropathies, such as Charcot-Marie-Tooth syndrome 4
Test Utilization
The utilization of these tests can vary depending on the clinical context and suspected underlying cause of neuropathy. For example, a study found that Medicare expenditures were significantly higher in the diagnostic period than in the baseline period, suggesting that diagnostic testing for neuropathy can be resource-intensive 3. Another study found that comprehensive multigene panel testing can provide a molecular diagnosis for a significant proportion of patients with neuropathy, highlighting the importance of genetic testing in certain cases 4.