Introduction

Infection is the single most likely cause of delayed healing in chronic wounds. In most cases, identification of chronic wound infection (eg, diabetic foot ulcers and venous leg ulcers) is not obvious because chronic wounds do not exhibit the same classic inflammatory signs of infection as those found in acute wounds. More arduously, those common signs of infection—pain, erythema, heat, and purulent exudate— vary as we age and occur differently in those with underlying diseases or weakened immune systems.

Diagnosis is generally based on the doctors’ experience and could be confirmed with microbiological culture of tissue biopsy. However, culture could take a few days, and the results may not always be reliable because of sampling error. A fast and accurate diagnosis of wound infection would relieve the patient of significant discomfort and improve the treatment outcome.

New Biomarker for Wound Infection Diagnosis

Given that an increase in leukocyte numbers and leukocyte esterase activity may accompany infection, several commercially available test strips are used for diagnosing urinary tract infection and peritonitis by detecting elevated leukocyte esterase levels in urine and peritoneal fluid, respectively. Unfortunately, these strips may not be suitable for assessing chronic wound infection, for several reasons:

• First, infection and elevated leukocyte esterase activity may occur only in certain areas of wounds.
• Second, application of these strips to chronic wounds may irritate the wound site and cause cross-site contamination.
• Finally, the binding of wound tissue debris and blood clots on the strips may make these strips unreadable.

To overcome these drawbacks, there is a type of noncontact device that detects elevated leukocyte esterase activity in chronic wounds. This sandwich-shaped device is designed for placement of a freshly recovered wound dressing between a testing layer and a holder layer.

Leukocyte esterase in the wound exudate on the dressing then reacts with a substrate on the testing layer to produce a color that can be seen through the transparent cover of the testing layer. Such a device can assess leukocyte esterase activity across full-sized wounds by avoiding direct patient contact and sampling variations. Depending on which color dominates the testing layer, this type of device could guide the physician either to continue with routine treatment or to prescribe a laboratory test.

New Noncontact Diagnostic Device Fares Well in the Clinic

Laboratory testing showed that this type of device can reliably assess leukocyte esterase activity across large surface areas. Moreover, this device can be used to visualize esterase activity within the human wound milieu, regardless of the type of wound dressing used.

The device was also clinically evaluated by correlating the device outcome with the clinical determination of infection by providers based on wound etiology, assessment, laboratory results, and treatment outcome. The preliminary results show that, for those wounds with clinical signs of infection, the device output increased the chance to identify wound infection by approximately 9%.¹ For those wounds without the clinical signs of infection, the device output would increase the probability of identifying infected wounds by approximately 16%. Because no device can diagnose wound infection at the point of care, the accuracy of the device output was compared with the clinical observations that were based on the clinical signs of infection.

Although the results show that the device output had better sensitivity than diagnosis based on the clinical signs of infection, it had lower specificity. Most importantly, however, the accuracy of wound infection diagnosis based on the device output was substantially better (79% vs 50%) than that based on the clinical signs of infection.¹ The results lend support to the use of the leukocyte esterase activity measuring device in improving the diagnosis of wound infection in the clinical setting.

Conclusion

Wound infection status cannot be concluded based on this type of device alone. However, this type of noncontact device may be used as an aid to providing rapid detection of elevated leukocyte esterase to assist wound care providers with their clinical assessment of infection in wounds. The combined enhanced infection diagnosis and fast device output may significantly improve wound care by quickly identifying infected wounds. The further development of the device may provide an invaluable tool for active management of wound infections because use of the device does not impinge on any routine procedures in the wound clinic.

Reference

1. Senkowsky J, Li S, Nair A, Pal S, Hu W, Tang L. A non-contact device for fast screening of wound infections. Exp Dermatol. 2021;30(9):1332-1339.

About the Author

Dr. Liping Tang received his B.S. in Biology from Tunghai University and M.S. in Marine Biology from National Taiwan University. He subsequently obtained Ph.D. degree in Biomedical Engineering and Chemical Engineering from the University of Minnesota. After finishing postdoctoral training at Albany Medical College, he became Assistant Professor at the Department of Pediatrics at Baylor College of Medicine, Houston, Texas. Currently, he is a Professor at the Department of Bioengineering at UTA. Dr. Tang's research interest is in the development of new devices or tools for diagnosing and treating various diseases at their early stage. Using biomedical engineering techniques, his group is actively working on creating different imaging probes, medical devices, and implants for quick screening and targeted treatments of those diseases. Dr. Tang’s expertise covers a broad area of implant biocompatibility, inflammation, infection, stem cells, tissue regeneration, and wound healing.