Clinicopathologic variables according to disease severity in dogs with heartworm disease

Background: Canine heartworm disease is associated with various clinicopathologic abnormalities; however, most previous studies have focused on comparisons between infected and non-infected dogs rather than differences according to disease severity. The American Heartworm Society (AHS) clinical classification reflects disease severity in clinical practice, but clinicopathologic changes based on this classification have not been fully characterized. This study aimed to evaluate clinicopathologic variables according to disease severity and to assess their associations with heartworm class in dogs with heartworm disease. Methods: This retrospective study included 35 dogs diagnosed with heartworm disease. Dogs were classified according to Amearican Heartworm Society guidelines into mild (class 1–2) and advanced (class 3–4) groups. Clinicopathologic variables, including complete blood count, electrolyte, serum chemistry, and thromboelastography (TEG) parameters, were compared between groups, and correlations with heartworm class were evaluated. Results: A total of 35 dogs were retrospectively analyzed and categorized into mild (class 1–2, n = 17) and advanced (class 3–4, n = 18) groups. Compared with the mild group, dogs in the advanced group had significantly higher RDW, BUN, AST, CREA, and thromboelastography reaction time (R), and significantly lower Na⁺, Ca²⁺, and Cl⁻ concentrations. Spearman correlation analysis showed that heartworm class was positively correlated with RDW (ρ = 0.550), BUN (ρ = 0.601), AST (ρ = 0.788), and R (ρ = 0.730), and negatively correlated with Na⁺ (ρ = -0.430), Ca²⁺ (ρ = -0.422), and Cl⁻ (ρ = -0.392) (all P < 0.05). CREA was significantly different between groups but was not significantly correlated with heartworm class. Conclusions: Clinicopathologic variables differed according to disease severity in dogs with heartworm disease. These findings suggest that selected variables may reflect increasing clinical severity and provide adjunctive information for clinical assessment. Further studies are needed to validate these associations.