Investigation of cell-free DNA in canine plasma and its relation to disease.

BACKGROUND: DNA is released from dying cells during apoptosis and necrosis. This cell-free DNA (cfDNA) diffuses into the plasma where it can be measured. In humans, an increase in cfDNA correlates with disease severity and prognosis. OBJECTIVE: It was hypothesized that when DNA in canine plasma was measured by emission fluorometry without prior DNA extraction, the concentration of cfDNA would increase with disease severity. ANIMALS: The diseased population consisted of 97 client-owned dogs. The clinically normal population consisted of nine client-owned dogs presenting for 'wellness screens', and 15 colony-owned Harrier Hounds. METHODS: Plasma cfDNA was measured by fluorometry without prior DNA extraction. The effects of ex vivo storage conditions were evaluated in plasma from two clinically normal dogs. In all other dogs, plasma was separated within two hours of collection. The association between the cfDNA concentration in hospitalized dogs and a variety of clinical, clinicopathological and outcome variables was tested. RESULTS: The concentration of cfDNA was reliably measured when plasma was separated within two hours of blood collection. The diseased dogs had significantly higher cfDNA than clinically normal dogs (P < 0.001), and the more severe the disease, the higher the cfDNA when severity was categorized according to the American Society of Anesthesiologists (ASA) status (P < 0.001). Dogs that did not survive to discharge had significantly higher cfDNA concentrations than survivors (P = 0.02). Conclusions/Clinical Importance: The concentration of cfDNA in the plasma of diseased dogs is associated with disease severity and prognosis. Measurement of canine cfDNA could be a useful non-specific disease indicator and prognostic tool.