High-Dose Hydrocortisone Treatment Does Not Affect Serum C-Reactive Protein (CRP) Concentrations in Healthy Dogs

SIMPLE SUMMARY: C-reactive protein (CRP) can be measured in serum and is a useful biomarker to diagnose inflammatory conditions (e.g., autoimmune diseases) and monitor the response to treatment in dogs. Because dogs with autoimmune diseases are often treated with high doses of glucocorticoids, a potential effect of this treatment on serum CRP concentrations—apart from the disease process—cannot be excluded. To address this knowledge gap, we measured serum CRP concentrations in five different time points in healthy dogs that were given either a high dose of a glucocorticoid (hydrocortisone) or a placebo over 28 days. We observed fluctuations in serum CRP concentrations in individual dogs during the study period, but the treatment did not significantly influence these fluctuations. Thus, confounding effects of corticosteroid administration on the interpretation of serum CRP concentrations as an inflammatory biomarker in dogs is unlikely, but this warrants confirmation by further studies. ABSTRACT: Measuring C-reactive protein (CRP) in serum is a useful surrogate marker for assessing disease progression and treatment response in dogs with autoinflammatory diseases. Affected dogs often receive high-dose glucocorticoid treatment, but the effect of such treatment alone on serum CRP concentrations is unknown. We evaluated serum CRP concentrations via immunoassay (sandwich enzyme-linked immunosorbent assay and particle-enhanced turbidimetric immunoassay) in 12 healthy beagle dogs administered high-dose hydrocortisone (8 mg/kg q12 h) per os vs. placebo over 28 days (days 0, 1, 5, and 28) in a randomized parallel study design. Serum CRP concentrations slightly decreased during treatment or placebo but without a significant association with hydrocortisone administration (p = 0.761). Compared to baseline, serum CRP concentrations were decreased by >2.7-fold (minimum critical difference) in three hydrocortisone-treated dogs and two dogs in the placebo group on day 28, whereas an increase to >2.7-fold was seen in one dog receiving placebo. These results suggest a lack of confounding effects of high-dose hydrocortisone administration on serum CRP concentrations in healthy dogs. This might also hold in dogs with autoinflammatory conditions and/or administration of other high-dose corticosteroids, suggesting that CRP presents a suitable biomarker to monitor inflammatory disease processes. However, this needs confirmation by further studies evaluating corticosteroid-induced cellular (e.g., hepatic) transcriptome and proteome changes.