Validation of a field-ready handheld meter for plasma -hydroxybutyrate analysis

Plasma metabolite analysis is frequently used to assess the energetic state and energy intake of birds. Plasma -hydroxybutyrate (BUTY) is a common metabolite used in these studies, and is correlated with fasting and mass loss. BUTY is typically quantified in laboratory assays that are costly, time-consuming, and prone to human error. We tested the accuracy and precision of a field-ready handheld BUTY meter. We compared BUTY concentration values obtained in the laboratory and with the handheld meter in plasma samples from 19 Grasshopper Sparrows (Ammodramus savannarum), and assessed precision with repeat analysis of a single sample. The handheld meter reported BUTY concentrations in <2min, was highly precise, and as accurate as the laboratory assay methodall ideal for field conditions. Collecting blood samples for laboratory analysis, particularly from remote field sites, involves a series of risks and challenges for permitting or the logistics of storage and shipping, as well as the associated costs. Analyzing samples on site, whether with the unit we tested or other similar handheld meters, makes plasma metabolite analysis practical and possible in field conditions and for taxa where this technique has been underused due to permitting, transport, or other logistical constraints of laboratory analysis methods. The cost of analysis is similar on a per sample basis, but, without the need to store and transport samples, using handheld meters in the field may be cheaper.