What laboratory tests are used to diagnose neuropathy?

From the Guidelines

Laboratory tests for neuropathy should include a complete blood count, comprehensive metabolic panel, hemoglobin A1C, vitamin B12 levels, folate levels, thyroid function tests, and erythrocyte sedimentation rate, as these help identify underlying causes such as diabetes, vitamin deficiencies, and autoimmune disorders. When evaluating patients for neuropathy, it is essential to consider the clinical presentation, medical history, and risk factors to guide the selection of laboratory tests. According to the most recent guidelines, such as those from the Diabetes Care journal 1, assessment for distal symmetric polyneuropathy should include a careful history and assessment of either temperature or pinprick sensation and vibration sensation using a 128-Hz tuning fork. Some key points to consider when ordering laboratory tests for neuropathy include:

• Screening for reversible neuropathy causes: diabetic screen, B12, folate, TSH, HIV, as recommended by the Journal of Clinical Oncology 1
• Considering serum protein electrophoresis and other vasculitic and autoimmune screens
• MRI of the spine with or without contrast, and considering neurology consultation
• For grade 2 neuropathy, MRI of the spine is advised, and MRI of the brain if cranial nerve involvement is suspected, as well as considering EMG/NCS, as outlined in the Journal of Clinical Oncology 1 It is crucial to tailor the diagnostic workup to the individual patient's needs, taking into account the severity of the neuropathy and the presence of any underlying conditions. By prioritizing the most recent and highest-quality evidence, such as the 2022 standards of medical care in diabetes 1, healthcare providers can ensure that patients receive appropriate and timely diagnosis and treatment for neuropathy, ultimately improving outcomes in terms of morbidity, mortality, and quality of life.

From the Research

Labs for Neuropathy

• Initial blood tests for neuropathy should include:
  • Complete blood count
  • Comprehensive metabolic profile
  • Measurement of erythrocyte sedimentation rate and fasting blood glucose
  • Vitamin B12 levels 2, 3
  • Thyroid-stimulating hormone levels 2, 3
• Specialized tests may be ordered if clinically indicated, such as:
  • Serum protein electrophoresis with immunofixation 3
  • Electrodiagnostic studies, including nerve conduction studies and electromyography 2, 3
• Lumbar puncture and cerebrospinal fluid analysis may be helpful in the diagnosis of certain conditions, such as Guillain-Barré syndrome and chronic inflammatory demyelinating neuropathy 2

Vitamin B12 and Neuropathy

• Vitamin B12 supplementation has been shown to improve neuropathic symptoms and reduce pain in patients with diabetic neuropathy 4, 5
• Normalizing vitamin B12 levels with oral supplementation has been found to improve sural nerve conduction velocity, sural nerve action potential, and vibration perception threshold in patients with diabetic neuropathy 5
• Reduced serum levels of vitamin B12 have been found in patients with type 2 diabetes and diabetic peripheral neuropathy compared to patients with type 2 diabetes but without neuropathy 6