Autonomic neuropathy is diagnosed through a combination of symptom questionnaires, cardiovascular reflex tests, sweat function tests, and targeted lab work to identify the underlying cause. There is no single test that confirms it. Instead, doctors build a picture by measuring how well your autonomic nervous system controls heart rate, blood pressure, sweating, digestion, and bladder function, then compare those results against known thresholds.
Symptom Screening Comes First
Before any specialized testing, your doctor will likely ask structured questions about symptoms across multiple body systems. A widely used tool is the COMPASS-31 questionnaire, which scores autonomic function across six areas: orthostatic intolerance (dizziness on standing), gastrointestinal symptoms, bladder problems, blood vessel regulation, pupil function, and sweat gland function. Scores range from 0 to 100, with a score above 12.5 generally flagging meaningful autonomic dysfunction. Scores above 20 suggest moderate to severe involvement.
The American Diabetes Association recommends autonomic neuropathy screening for all people with type 2 diabetes starting at diagnosis, and for people with type 1 diabetes beginning five years after diagnosis, with at least annual checks after that. Screening should also happen whenever there’s evidence of other nerve or kidney damage from diabetes.
Cardiovascular Reflex Testing
The heart and blood vessels are controlled heavily by the autonomic nervous system, so cardiovascular tests are the cornerstone of diagnosis. These are typically done in a specialized autonomic lab, though some can be performed at the bedside.
Heart Rate Response to Deep Breathing
Your heart rate naturally speeds up when you breathe in and slows down when you breathe out. During this test, you breathe at a controlled pace of about six breaths per minute while your heart rate is monitored beat by beat. In a healthy person, the difference between the fastest and slowest heart rate during this cycle is more than 15 beats per minute. A difference of 10 beats per minute or less points to autonomic dysfunction. This is one of the simplest and most sensitive early markers of cardiovascular autonomic damage.
The Valsalva Maneuver
You blow into a tube at a set pressure for about 15 seconds, which temporarily changes the pressure inside your chest and triggers a chain of blood pressure and heart rate adjustments. Doctors track the beat-by-beat changes in both. The key measurement is how much your heart rate changes in response to each unit of blood pressure change during the strain. When the autonomic system is working correctly, the heart rate swings are brisk and proportional. In autonomic failure, these reflexes are blunted or absent. While older methods simply compared peak and minimum heart rates (the “Valsalva ratio”), modern testing looks at the full blood pressure and heart rate relationship for a more accurate picture.
Orthostatic Blood Pressure Testing
This test measures what happens to your blood pressure and heart rate when you move from lying down to standing, either by simply standing up or by being tilted upright on a motorized table. A drop in systolic blood pressure of 20 mmHg or more, or a drop in diastolic pressure of 10 mmHg or more, is considered abnormal. If your blood pressure drops that much but your heart rate fails to increase to compensate, that combination is a strong indicator of autonomic dysfunction rather than simple dehydration or medication side effects.
Tilt table testing typically lasts 10 to 45 minutes with continuous monitoring. Some people develop symptoms like lightheadedness, nausea, or near-fainting during the test, which is useful diagnostic information in itself.
Sweat Function Tests
The autonomic nervous system controls sweating, so measuring sweat output can reveal damage to the small nerve fibers that regulate your sweat glands. Two main tests are used.
Quantitative Sudomotor Axon Reflex Test (QSART)
Small capsules are placed on your skin at standard locations (usually the forearm, lower leg, and foot). A mild electrical current pushes a sweat-stimulating chemical into the skin. This chemical activates nerve endings in two ways: it directly triggers nearby sweat glands, and it also sends a signal along the nerve fiber that branches out and activates a wider ring of sweat glands through what’s called an axon reflex. The sweat produced by this indirect route is what the test actually measures, because it depends on intact nerve fibers to work. Reduced or absent sweat output at specific sites maps to where nerve damage has occurred. The test takes about an hour and the electrical stimulation feels like mild tingling.
Thermoregulatory Sweat Test (TST)
This test looks at the bigger picture of whole-body sweating. You lie on a table and are dusted with a powder that changes from yellow to bright purple wherever you sweat. The room’s temperature and humidity are then raised to trigger sweating across your entire skin surface. A camera records the color change pattern, creating a body map that shows exactly which regions are sweating normally and which are not. The pattern of dry (still yellow) areas helps doctors determine whether nerve damage follows a specific anatomical distribution, such as a length-dependent pattern starting at the feet and hands, or a patchy pattern suggesting a different type of nerve injury.
Gastrointestinal Testing
Autonomic neuropathy frequently slows the digestive tract, particularly the stomach. The standard test for this is a gastric emptying study. You eat a small meal (usually scrambled eggs or oatmeal) that contains a tiny amount of radioactive tracer, then sit under a scanner that tracks how quickly the food leaves your stomach over four hours.
Normal stomach emptying means no more than 60% of the meal remains at two hours, and no more than 10% remains at four hours. If your stomach retains more than those thresholds, you have delayed gastric emptying, commonly called gastroparesis. This test is important because gastroparesis affects medication absorption, blood sugar control, and nutrition, all of which factor into treatment planning.
Bladder Function Assessment
Autonomic nerve damage can impair the bladder’s ability to sense fullness and contract properly, leading to incomplete emptying. A post-void residual volume measurement, done with a quick bladder ultrasound right after you urinate, quantifies how much urine is left behind. Less than 100 mL is normal. Up to 200 mL may be acceptable depending on context. Over 200 mL indicates inadequate emptying, and over 400 mL is diagnostic of urinary retention. This is a painless, noninvasive test that takes a few minutes.
Pupil Testing
Your pupils are controlled by autonomic nerves, with one set dilating them and another constricting them. During a bedside exam, your doctor shines a light into your eyes and watches how quickly and completely the pupils respond. In autonomic neuropathy, a characteristic finding called Adie’s pupil can appear: the affected pupil is larger than normal, responds poorly to light, and constricts slowly and incompletely when you try to focus on something close. Specialized instruments called pupillometers can measure the speed and degree of pupil response more precisely than visual observation alone.
Blood Tests to Identify the Cause
Once autonomic testing confirms dysfunction, lab work helps pinpoint why the nerves are damaged. The specific tests ordered depend on the clinical picture, but the workup commonly includes fasting blood glucose and an oral glucose tolerance test (since diabetes is the most common cause), along with tests directed at other suspected conditions. If dry eyes and dry mouth are present, antibody tests for Sjögren syndrome may be checked. A rapid onset of symptoms might prompt testing for antibodies against nerve receptors involved in autonomic signaling. When neuropathy is accompanied by confusion and abdominal pain, urine testing for porphyria may be appropriate.
Genetic testing is available for hereditary forms of autonomic neuropathy, and measuring baseline levels of norepinephrine (a chemical messenger used by autonomic nerves) can help distinguish between different types of autonomic failure. The goal of this lab workup is to find treatable or reversible causes rather than simply confirming that neuropathy exists.
How Tests Are Combined for Diagnosis
No single test is sufficient on its own. A typical autonomic evaluation at a specialized center includes cardiovascular reflex testing (deep breathing, Valsalva, and tilt table) plus sudomotor testing (QSART or TST), with additional organ-specific tests added based on your symptoms. The cardiovascular tests assess the nerves controlling your heart and blood vessels, the sweat tests assess small fiber function, and organ-specific tests (gastric emptying, bladder ultrasound) document the functional consequences of nerve damage.
Results are often graded on a severity scale. Mild autonomic neuropathy might show up only as reduced heart rate variability during deep breathing. Moderate cases typically add abnormal Valsalva responses or reduced sweat output. Severe autonomic neuropathy usually involves measurable orthostatic hypotension along with widespread sudomotor failure and organ dysfunction. This grading helps guide treatment decisions and gives you a baseline for tracking whether the condition is stable, improving, or progressing over time.