Why test sudomotor function?

“Sweat response may be the most sensitive test in detecting distal small fiber neuropathy” (see publications by Low et al. and Gibbons et al). Eccrine glands that are responsible for sweat response receive a rich supply of blood vessels and are innervated by sympathetic C nerve fibers (autonomic nervous system). These fibers are thin and long and so can be impaired at the early stage of different metabolic diseases. Testing sudomotor function can be a fast and accurate method for detecting early stages of neuropathies.




SUDOSCAN is a medical device has been cleared by the FDA as a galvanic
skin response test. Galvanic Skin Response (GSR) is a change in the
electrical properties of the skin in response to different kinds of
stimuli. In GSR, changes in the voltage measured from the surface of the
skin are recorded. The main origin of the signal has suggested to be the
activation of sweat glands (sudomotor function).


What does SUDOSCAN measure?

SUDOSCAN evaluates sudomotor function on the palm of the hands and sole of the feet where the density of sweat glands is maximal.

The underlying technology is based on established principles on the electrochemical reaction between chloride (found in sweat) and nickel (which is a component of the electrodes used in SUDOSCAN). A low DC voltage ≤ 4 volts is applied generating a current relative to chloride (ion) flow supplied by the sweat glands and ducts. An Electro Skin Conductance (ESC) is calculated for the hands and feet on this basis of the current generated and the voltage supplied.

Similar to cardiologic stress test for which the exercise is used as a stimulus to capture specific information that is not assessable in resting state, SUDOSCAN too relies on an electrical stimulus of sweat chloride to capture information about the sweat dysfunction that cannot be diagnosed in usual conditions. For a better understanding see animation on the web site.

Because the skin’s stratum corneum acts like an electrical capacitor allowing only the conduction of chloride to pass to the surface hands and feet electrodes via the sweat duct when a low voltage stimulation is applied, we can be certain that we’re targeting the underlying sweat gland and its sympathetic innervations.

This underlying theory has been confirmed in a comparative study performed on patients with Cystic Fibrosis (who have high sweat chloride concentration) and controls (see publication by Hubert et al).


Who should get tested on SUDOSCAN?

Anyone can get tested on SUDOSCAN to assess their sudomotor function unless they have a specific contra-indication that would prevent them from performing a scan. As previously described, the potential uses for SUDOSCAN include evaluation of peripheral neuropathy and follow-up for diabetic patients.


What are the reasons to get yourself tested on SUDOSCAN?

Small C fiber nerve damage can be observed in subjects with prediabetes or metabolic syndrome.  Because SUDOSCAN is non-invasive and takes only 3 minutes to run, you can benefit from knowing your hands and feet conductances – in first establishing your baseline levels, then repeating the test periodically to monitor your numbers.  SUDOSCAN allows you to have:

  • Immediate knowledge of sweat gland functioning as indicator of peripheral nerve functioning
  • Biofeedback: a way to quantify the “status” of your peripheral nerves upon lifestyle changes ex. Exercise and its benefits


What information does SUDOSCAN provide? How can the physician use this information to help his/her patient?

SUDOSCAN test results are provided in hands and feet conductances.  High conductances correlates with normal sweat function and healthy nerve innervation (small C-fibers).  Low conductances represent peripheral or autonomic neuropathy.

Physicians can use SUDOSCAN in various medical settings:

  • Proactive monitoring: Medicine is trending towards prevention of the onset of a disease or complication.  Since the long, unmyelinated, sympathetic c-fibers slowly degenerate yet quickly regenerate with changes (good or bad) in a patients environment; physicians can use this information to determine whether or not a patient is “at risk” of developing a complication and take proactive measures with treatment options.
  • Assessing the level of intensive glycemic control for diabetics.  It is important to determine whether or not a patient has a neuropathy before prescribing intensive forms of glycemic treatment.
  • Patient drug or lifestyle compliance: SUDOSCAN allows for a physician to quickly determine Sudomotor functioning as a biomarker for peripheral nerve integrity.  Patient compliance can quickly be determined based on how good or how bad their results are.  This information is complimentary to traditional blood based testing, but is extremely fast and offers immediate results.  Quantitative results introduce no subjectivity via patient verbal responses.


Does gender play a factor in the results?

Evaluation of sudomotor function using other tests such as QSART has shown generally lower measures (in sweat output) in women compared with those on men. This can be explained by lower sweat rates in women. Measurements performed by SUDOSCAN don’t depend on sweat rate. A study performed on more than 500 women and more than 200 men show no significant differences in hands’ and feet’ ESC. This will be confirmed in future pending studies on larger group populations.


Does ethnicity play a role?

Sweat rate can vary with ethnicity. As previously mentioned, SUDOSCAN measurements do not depend on sweat rates. Studies that have been performed in India, China, Germany, France and other European countries show no notable differences in hands and feet ESC in Asian subjects as compared with European subjects. However larger studies are necessary to confirm this hypothesis.


Can my age influence the SUDOSCAN reading?

SUDOSCAN measured conductance levels do not depend on age.


Does room temperature affect the test results?

Clinical tests run at different temperatures (changes of more than 5°C) demonstrate that temperature variance do not have impact on test results. Hands and feet that are poorly involved in thermoregulation due to their small area and thus are less temperature dependent than other parts of the body for their sweat rate.

Theoretically, extreme cold temperature on the electrodes could result in vasoconstriction, whose effect has not been yet studied. Therefore, avoid performing test measurements if the electrodes are too cold.


Does exercising just before being evaluated impact test results?

Given sweat rate changes with exercise it was important to evaluate the effects of exercise on SUDOSCAN tests. Measurements were performed before and after high level exercise on more than 100 subjects. Tests show a coefficient of variation of 13 % for the hands and of 4% for the feet between these two measurements. These results confirm that SUDOSCAN measurements are not dependent on sweat rate.


Can I use Sudoscan for type 1 diabetes?

Contrarily to type 2 diabetes, diagnosis of type 1 can occur before the onset of complications including small C-fiber neuropathies. Thus at the early stages of the disease if the patient treatment is well-balanced sweat function should be normal and conductances values as measured by SUDOSCAN should not be decreased.  However with the progress of the disease, especially if the patient treatment is not fully adapted, small C-fibers damages will occur and sweat dysfunction should be evidenced through a decrease in conductances as measured by SUDOSCAN. Due to the absence of pre-diabetes stage small C-fiber damages can be lower and occur at later stages as compared to type 2 diabetes.


Can children be tested?

There is no safety concern testing children on SUDOSCAN. However due to hormonal changes in children, it is difficult to produce consistent and accurate ESC readings. We recommend children under the age of 18 not to be scanned due to fluctuations in conductance levels.


How does SUDOSCAN correlate with HbA1c?

HbA1C is used to monitor glycemic levels for the past 3 month period. SUDOSCAN is not a blood-based test but focuses on the assessment of the small C nerve fibers.  As such, SUDOSCAN is a test that can be performed in complement to HbA1c. There is no strict correlation evidenced between HbA1C and Sudocan results.  In research studies performed, we’ve observed cases where there were significant differences in SUDOSCAN results yet no differences measured by HbA1c testing.


How does SUDOSCAN correlate with EMG testing?

SUDOSCAN is used for small fiber neuropathy evaluation. EMG is used to test large fibers.


Is SUDOSCAN reimbursed? And how much?

Yes. Medicare and Medicaid are consistent with their good reimbursement for this test.  The level of reimbursement varies depending on geography and payer.  In many states such as New York where SUDOSCAN is currently used, physicians have been very satisfied with the level of reimbursement.


How often can you or should you retest?

Retest based upon Sudocan results and physician recommendations.  If your conductances are within normal tolerances, retesting every 9 to 12 months is typical. Patients with peripheral neuropathies can be tested every three months to follow-up treatment protocols.


Is SUDOSCAN part of the protocol regiment for physicians today?

At the moment physician have no tools to quickly and easily screen peripheral neuropathy, other the use of biopsy methods that are clearly invasive in nature.  Skin biopsies are not performed routinely, especially on diabetic patients with feet lesions.  This leaves SUDOSCAN, which has huge potential to be used by physicians to follow-up patients with Type 2 diabetes as part of the ADA guidelines.


Who is using SUDOSCAN today?

SUDOSCAN is used in clinical settings by general practitioners and specialists throughout the US.  SUDOSCAN is also proving to be an invaluable research tool for hospitals and major study centers in clinical studies. It is currently deployed in a dozen institutions and being received with enormous praise by key opinion leaders in the fields of neuropathy, nephropathy, endocrinology and cardiology.


Can I get tested if I have a pace-maker?

Since only direct current is applied during a SUDOSCAN test, it does not
interfere with pace-maker electronics; therefore SUDOSCAN should be safe to use
in a subject with a pace-maker.

To confirm that there is no safety concern tests have be performed to check
Electromagnetic Compatibility according to ANSI/AAMI PC69:2007 : Active implantable
medical devices— Electromagnetic compatibility— EMC test protocols for
implantable cardiac pacemakers and implantable cardioverter guidelines.
Conclusion of the tests performed by Laboratoire Centrale des Industries
Electriques (LCIE, Fontenay aux Roses, France) is that “SUDOSCAN is compliant
according to ANSI/AAMI PC69: 2007 (Annexe M) standard”. (Report October, 2012).

However we recommend that patients with pace-makers perform Sudocan testing
in the presence of a medical doctor.


What if I’m on Beta blockers ?

Beta-blocker that are now cardioselective should not interfere with
SUDOSCAN measurements. However additional testing is needed to confirm this and
the potential effect of other cardiovascular drug.


What if I’m on anti diabetic drugs?

At the moment an observational study performed in an outpatient consult
clinic in Germany on two groups of patients with type 2 diabetes, the first one
receiving insulin, the second one other anti-diabetic drugs evidenced that after
one-year follow-up patients receiving insulin had an improvement in their
conductances while the others had a small decrease. These preliminary results
have to be confirmed in a clinical study performed on a larger population.