Testing for neuropathy typically starts with a physical exam and blood work, then moves to specialized electrical tests or biopsies depending on what your doctor finds. The process is layered: first confirming that nerve damage exists, then measuring how severe it is, and finally identifying what’s causing it. Most people will go through at least two or three types of testing before getting a complete picture.
The Physical Exam
A neurological exam is usually the first step, and it can reveal a surprising amount about which nerves are affected. Your doctor will test several systems in sequence: sensation, strength, and reflexes.
For sensation, you’ll feel a series of stimuli applied to your skin, usually starting at your feet and working upward. A thin nylon fiber called a monofilament is pressed against the sole of your foot to test light touch. Pinprick testing checks whether you can distinguish sharp from dull. A vibrating tuning fork placed against your anklebone or big toe tests whether the large sensory fibers that detect vibration are intact. Temperature sensation may also be checked with warm and cool objects.
Reflexes are tested at several points: the ankle, knee, bicep, and tricep. Each reflex corresponds to a specific level of the spinal cord. Doctors grade reflexes on a scale from 0 (completely absent) to 5 (abnormally overactive). In most peripheral neuropathies, reflexes are diminished or absent, particularly at the ankle. A muscle strength exam rounds out the picture, with your doctor asking you to push or pull against resistance to detect any motor nerve involvement.
The monofilament test is widely used as a screening tool for diabetic neuropathy, but it has real limitations. A large multicenter study found it catches only about 60% of cases, meaning it misses nearly half of people who actually have nerve damage. Its strength is ruling neuropathy in rather than ruling it out: when it does detect a problem, it’s right about 82% of the time.
Blood Tests to Find the Cause
Once nerve damage is suspected, blood work helps identify what’s driving it. A standard initial panel includes a complete blood count, a comprehensive metabolic panel, fasting blood sugar, vitamin B12, thyroid hormone levels, and a marker of inflammation called the sedimentation rate. These six tests alone can flag the most common culprits: diabetes, B12 deficiency, thyroid disease, and kidney or liver dysfunction.
If those come back normal or your symptoms don’t fit a typical pattern, your doctor may order more targeted tests. Hemoglobin A1C or a glucose tolerance test can catch prediabetes that a fasting glucose missed. Protein electrophoresis looks for abnormal proteins in the blood that can damage nerves. Antibody tests can screen for autoimmune conditions like lupus or Sjögren syndrome, infections like HIV, Lyme disease, or syphilis, and inflammatory conditions like sarcoidosis. In rare cases, genetic testing, spinal fluid analysis, or panels for cancer-related nerve damage may be warranted.
Nerve Conduction Studies and EMG
Electrodiagnostic testing is the backbone of neuropathy diagnosis. It objectively measures how well your nerves transmit electrical signals and how your muscles respond. Two tests are usually performed together in the same appointment.
A nerve conduction study involves placing small electrodes on your skin over a nerve. One electrode delivers a mild electrical pulse, and recording electrodes placed over the muscles controlled by that nerve measure how quickly and strongly the signal arrives. The speed of that signal, called conduction velocity, tells your doctor whether the nerve’s insulating coating is damaged. The strength of the signal indicates whether nerve fibers themselves have been lost. Both pieces of information help distinguish between different types of neuropathy.
Electromyography, or EMG, follows the nerve conduction study. A thin needle electrode is inserted into specific muscles to record their electrical activity as you contract and relax them. Healthy muscles produce a characteristic pattern. Damaged nerves create abnormal signals in the muscles they supply, which can reveal whether the damage is recent or longstanding, and which specific nerves are involved.
Preparing for EMG Testing
Skip lotions, creams, and perfume on the day of your test, as they interfere with electrode contact. Wear loose, comfortable clothing. If you take blood thinners, let the testing provider know ahead of time since the needle portion carries a small bleeding risk. You may also be asked to avoid caffeine and cigarettes for two to three hours before the test. If you have a pacemaker or any implanted electrical device, mention that as well.
The electrical pulses feel like brief static shocks, and the needle portion can cause mild discomfort similar to an acupuncture needle. The whole session typically takes 30 to 60 minutes.
Skin Biopsy for Small Fiber Neuropathy
Nerve conduction studies only detect problems in large nerve fibers. If your symptoms point to small fiber neuropathy (burning pain, temperature sensitivity, or abnormal sweating) but your nerve conduction results look normal, a skin biopsy can confirm the diagnosis.
The procedure is straightforward. A small circular punch of skin, usually about 3 millimeters, is taken from the lower leg under local anesthesia. In the lab, technicians count the number of tiny nerve fibers that cross from the deeper skin layer into the outer layer, called the epidermis. That count is expressed as a density (fibers per millimeter) and compared against published norms matched for your age and sex. A significantly low density confirms small fiber neuropathy. This test reliably detects nerve damage from diabetes, HIV, lupus, and other systemic conditions that preferentially target small fibers.
Autonomic Nerve Testing
Some neuropathies affect the nerves that control involuntary functions like heart rate, blood pressure, digestion, and sweating. If you have symptoms like lightheadedness on standing, abnormal sweating patterns, or digestive problems alongside your neuropathy, autonomic testing can assess these nerves specifically.
A sweat test (called QSART) measures how your sweat glands respond to a mild electrical stimulus. Electrodes containing a sweat-stimulating substance are placed on your foot, leg, and wrist. A computer analyzes how your nerves and sweat glands react. The full test takes about 45 minutes to an hour.
Heart rate variability tests evaluate the nerves controlling your cardiovascular system. In a deep breathing test, you breathe slowly for one minute while electrodes on your chest and a finger blood pressure cuff track how your heart rate and blood pressure respond. A healthy autonomic nervous system produces noticeable heart rate changes with each breath. The Valsalva maneuver, where you exhale forcefully through a mouthpiece with your nose pinched, tests a similar reflex. Blunted responses to either test suggest autonomic nerve damage.
Quantitative Sensory Testing
Quantitative sensory testing, or QST, measures your sensory thresholds with precision that a bedside exam can’t match. Rather than asking “can you feel this?” with a tuning fork, QST uses calibrated devices to determine the exact point at which you detect vibration, warmth, coolness, or pain.
Vibration thresholds are tested using a device that starts at a high intensity and decreases by 10% after each correct response, zeroing in on the faintest vibration you can perceive. Thermal testing works similarly: a probe on your skin gradually warms or cools from a baseline of about 34°C, and you indicate the moment you feel the change. The test can separately measure your thresholds for warmth, coolness, heat pain, and cold pain.
Different sensory channels map to different nerve fiber types. Vibration and light touch travel through large insulated fibers, while temperature and pain signals travel through small or uninsulated fibers. By testing across all these channels, QST can help identify which fiber populations are affected even before other tests show abnormalities.
Imaging: Ultrasound and MRI
When doctors suspect a nerve is being physically compressed or trapped rather than damaged by a systemic disease, imaging can pinpoint the problem. Ultrasound provides real-time, high-resolution views of peripheral nerves and is less expensive than MRI. It measures the nerve’s cross-sectional area at different points along its course. A nerve that’s swollen at one location but normal-sized elsewhere suggests entrapment, as in carpal tunnel syndrome where the median nerve enlarges at the wrist. Ultrasound is particularly useful for small, superficial nerves and for dynamic assessment, where the nerve is watched as you move the affected limb.
MR neurography is a specialized MRI technique that produces detailed images of deeper nerves, like the brachial plexus in the shoulder region. It can reveal nerve swelling, inflammation, and surrounding scar tissue. For conditions like thoracic outlet syndrome, images are taken in both a neutral position and with the arm raised and rotated outward, allowing doctors to see whether the nerve is being compressed during specific postures. Imaging doesn’t replace electrical testing but complements it by showing the structural “why” behind abnormal function.