Determining the age of human bruises

Abstract

Evidence of physical abuse can often be found on the skin of victims, with bruising being the most common symptom. Bruises are also the most frequent injury sustained in sports and everyday accidents, affecting both males and females of all ages. The widespread occurrence of bruises sometimes leads to abusive or accidental bruises being misdiagnosed. In cases where multiple bruises are found on the skin of a potential abuse victim, determining that these are of different ages, and were therefore inflicted on different occasions, could provide significant evidence to medico-legal cases concerning physical abuse. This would be particularly valuable in situations involving vulnerable individuals, such as children or elderly people, who may be unable, or unwilling, to provide an accurate account of the circumstances, or timing, of an assault. Here, we describe the proteomic analysis of proteins present in interstitial fluid, collected from under the surface of the skin, in an attempt to identify candidate protein biomarkers specific to bruising in living individuals. Samples were collected using a minimally invasive, ultrasonic skin permeation device in combination with an interstitial fluid collection system. Samples were compared with differential in-gel electrophoresis, which allowed the detection and mass spectrometric identification of proteins specific to bruising. The expression of the protein markers identified changed significantly in bruised skin compared to unbruised skin, as well as over time as the injury healed. Markers were validated with western blots and tested with enzyme-linked immunosorbent assays to assess their expression in bruised skin over time. This analysis is the first of its kind to employ interstitial fluid for the search of biomarkers specific to bruising, providing the first steps towards a technique that could allow medical practitioners and police investigators to estimate when a bruise was inflicted on a living individual. In addition, this work provides new insight into how the skin heals and reveals protein level changes following blunt force trauma to the skin. This work could include clinical research into skin physiology and infection, and the mechanisms of healing; sports medicine could also benefit from this work.