In the June 2024 study titled Diagnostic Performance of the Neuropad Test for the Screening of Distal Symmetric Polyneuropathy and Cardiovascular Autonomic Neuropathy in Patients with Diabetes, published by the Multidisciplinary Digital Publishing Institute (MDPI), researchers from two specialist centres in Greece evaluated the effectiveness of the Neuropad test in identifying diabetic autonomic neuropathy (DAN).
The study found that this simple, sweat-based, colour-changing diagnostic patch demonstrates high sensitivity and practical utility as a rapid screening tool for both early and advanced autonomic dysfunction in diabetic patients.
Diabetic autonomic neuropathy (DAN), and especially its cardiovascular form (CAN), is both common and critically important, yet frequently overlooked-particularly in its asymptomatic early stages. The diagnostic gold standard comprises specialized cardiovascular autonomic reflex tests (CARTs), such as heart‑rate variability, Valsalva ratio, orthostatic R‑R variability, and postural hypotension assessments. Despite their efficacy, these tests are resource‑intensive, require trained personnel, and are ill‑suited for routine clinical use.
An early harbinger of autonomic dysfunction is impaired sudomotor function-i.e., reduced sweat gland activity-mediated by postganglionic sympathetic cholinergic fibres. These changes are detectable in a “stocking and glove” distribution and manifest before overt CAN develops. Measured easily, impaired sweating reflects early sympathetic compromise and offers a window for screening.
The Neuropad® test is a visually interpretable, sweat‑sensitive plaster that patients can self‑administer. It contains cobalt (II) chloride, originally blue, which turns pink upon hydration. Applied to the foot for 10 minutes at room temperature (20-25 °C), full colour change indicates normal sweating, while incomplete or absent change signals dysfunction.
In a prospective study of 180 adults with diabetes (mean age 49.5), including 82 with type 1 and 98 with type 2, researchers compared Neuropad® results to established CARTs. DAN was defined by the presence of two or more abnormal CARTs.
Key Findings
- Sensitivity of Neuropad® for detecting established DAN was 87.1%, with a specificity of 78.9% and overall accuracy of 82.3%. These values remained robust across diabetes types: 83.9% sensitivity and 94.1% specificity in type 1, and 88.9% sensitivity and 61.4% specificity in type 2.
- Higher numbers of abnormal CARTs correlated with even greater Neuropad® accuracy, reinforcing its ability to detect more severe neuropathic states.
- For early parasympathetic dysfunction (abnormal MCR), Neuropad® demonstrated 73.3% sensitivity and 90% specificity; for postural hypotension (a symptom of advanced sympathetic failure), it achieved 93.3% sensitivity and 77.1% specificity.
When compared to prior studies, this work underscores the robust diagnostic performance shown by Neuropad®. While some earlier research reported lower specificity (33-66%), especially in type 2 diabetes, this study’s higher specificity-especially in type 1-supports its utility. Moreover, consistent with small‑fibre neuropathy and foot ulcer risk screening studies, high sensitivity values (~99%) have been documented, further adding to the body of evidence.
Advantages of Neuropad®
- Rapid and cost-effective: At just 10 minutes and simple colour interpretation, Neuropad® can be integrated into routine clinics or deployed as a patient-administered home test.
- High sensitivity: As is desirable for a screening test, Neuropad® excels at identifying individuals with early or advanced DAN, facilitating timely referral for more definitive CART evaluation.
- Patient empowerment: The ease and clarity of the test promote patient engagement, making it valuable in self-care and follow-up settings.
Clinical Implications
With its strong sensitivity and user-friendly format, Neuropad® is poised to fill a gap in early DAN screening. By rapidly flagging patients with potential autonomic dysfunction, it enables timely downstream evaluation, potentially mitigating progression to serious complications such as cardiovascular events or foot ulceration.
Moreover, the cost-effectiveness of Neuropad®, already recognized in peripheral neuropathy screening, along with its ease of use, supports its value in both primary care and specialist settings.
Conclusion
This study robustly supports Neuropad® as an effective screening instrument for diabetic autonomic neuropathy. Its high sensitivity and accuracy-even amid type 2 diabetes comorbidities-underscore its role in early detection protocols.