Abstract
Glucose is an important metabolic fuel and circulating levels are tightly regulated in most mammals, but can drop when body fuel reserves become critically low. Glucose is mobilized rapidly from liver and muscle during stress in response to increased circulating cortisol. Blood glucose levels can thus be of value in conservation as an indicator of nutritional status and may be a useful, rapid assessment marker for acute or chronic stress. However, seals show unusual glucose regulation: circulating levels are high and insulin sensitivity is limited. Accurate blood glucose measurement is therefore vital to enable meaningful health and physiological assessments in captive, wild or rehabilitated seals and to explore its utility as a marker of conservation relevance in these animals. Point-of-care devices are simple, portable, relatively cheap and use less blood compared with traditional sampling approaches, making them useful in conservation-related monitoring. We investigated the accuracy of a hand-held glucometer for 'instant' field measurement of blood glucose, compared with blood drawing followed by laboratory testing, in wild grey seals (Halichoerus grypus), a species used as an indicator for Good Environmental Status in European waters. The glucometer showed high precision, but low accuracy, relative to laboratory measurements, and was least accurate at extreme values. It did not provide a reliable alternative to plasma analysis. Poor correlation between methods may be due to suboptimal field conditions, greater and more variable haematocrit, faster erythrocyte settling rate and/or lipaemia in seals. Glucometers must therefore be rigorously tested before use in new species and demographic groups. Sampling, processing and glucose determination methods have major implications for conclusions regarding glucose regulation, and health assessment in seals generally, which is important in species of conservation concern and in development of circulating glucose as a marker of stress or nutritional state for use in management and monitoring.
Highlights
Development of rapid, field accessible and informative markers of stress and nutritional state are useful for conservation efforts in vertebrate species
We investigated the accuracy of a hand-held glucometer for ‘instant’ field measurement of blood glucose, compared with blood drawing followed by laboratory testing, in wild grey seals (Halichoerus grypus), a species used as an indicator for Good Environmental Status in European waters
Absolute and percentage discrepancy of the venous glucometer reading relative to the plasma glucose concentration is shown in Fig. 1b and c
Summary
Development of rapid, field accessible and informative markers of stress and nutritional state are useful for conservation efforts in vertebrate species. Significant deviations in blood glucose levels can cause serious acute and chronic metabolic disturbance and cell death Chronically elevated glucose levels may result from persistent, repeated stress or cortisol exposure (Barton et al, 1987; Khani and Tayek, 2001), whereas fasting and depletion of body energy reserves can lower circulating glucose (Cherel et al, 1988). Glucose levels correlate with habitat quality, reproductive state and/or body condition in many bird species (Fairbrother et al, 1990; Ruiz et al, 2002; Lill, 2011; Minias and Kaczmarek, 2013; Kalinski et al, 2014), and can be useful as an indicator of stress, condition or nutritional status in a conservation context
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