ORIGINAL ARTICLE A new method of screening for diabetic neuropathy using laser Doppler and photoplethysmography Sung Woo Kim Soo Chan Kim Ki Chang Nam Eun Seok Kang Jae Jung Im Deok Won Kim Received: 22 November 2006 / Accepted: 7 September 2007 / Published online: 10 October 2007 Ó International Federation for Medical and Biological Engineering 2007 Abstract The purpose of this study is to suggest a simple, new method of screening for diabetic neuropathy. We measured blood volume changes by photoplethysmography (PPG) and blood perfusion by laser Doppler (LD) in the index fingers and big toes in 40 control subjects and in 50 (19 mild, 17 moderate, and 14 severe based on the nerve conduction velocity (NCV) test) and 35 diabetic patients with and without neuropathy, respectively. According to the results of PPG and LD measurements, the toe to finger ratios obtained from the neuropathic group were signifi- cantly higher than those from the control (p \ 0.001) and the non-neuropathic groups (p \ 0.001). Based on the NCV, the sensitivity of the LD method (92.0%) was higher than that of the PPG method (84.0%) for both left and right sides. Although specificity of the LD (92.8%) was also higher than the PPG (84.3%) bilaterally, the PPG showed better reproducibility (5.5 versus 9.5%) and a significant ratio increase with severity, while the LD did not. Our suggested PPG method using the toe to finger ratio is reliable, simple, economical, and accurate, and could become an effective new screening tool for the early detection of diabetic neuropathy. Keywords Diabetic neuropathy  Photoplethysmography  Laser Doppler  Blood volume change  Toe to finger ratio 1 Introduction The incidence of diabetes is increasing dramatically due to economic development and lifestyle changes. The Growth from Knowledge (GfK) market measures (US Diabetes Patient Market Study, 2005) reported that the diabetic population in the United States had increased by approxi- mately 86% over the past decade. The Korean Diabetes Association (Ministry of Health and Welfare, Korean Institute of Health and Society, 2004) reported that the Korean diabetic population increased approximately ten- fold from 1970 to 2001. Among many other diabetic complications, diabetic foot disease is considered one of the most serious as it may cause ulceration and subsequent amputation of the legs. It was reported that approximately 30,000 diabetic patients undergo foot surgery each year in the United States [5]. Amputations, however, are prevent- able by early diagnosis. The causes of diabetic foot disease include neuropathy, neuro-ischemia, and ischemia. Of these etiologies, S. W. Kim  D. W. Kim (&) Department of Medical Engineering, College of Medicine, Yonsei University, Seoul 120-752, South Korea e-mail: kdw@yuhs.ac URL: http://ybil.yonsei.ac.kr/ S. C. Kim Graduate School of Bio and Information Technology, Hankyong National University, Anseong, South Korea K. C. Nam National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan E. S. Kang Division of Endocrinology and Metabolism, Department of Internal Medicine, College of Medicine, Yonsei University, Seoul, South Korea J. J. Im Division of Electronics and Information Engineering, Chonbuk National University, Chonju, South Korea 123 Med Bio Eng Comput (2008) 46:61–67 DOI 10.1007/s11517-007-0257-z