Serum Thymidine Kinase 1, Canine‐C‐Reactive Protein, Haptoglobin, and Vitamin D Concentrations in Dogs with Immune‐Mediated Hemolytic Anemia, Thrombocytopenia, and Polyarthropathy

BACKGROUND: Relapses of immune‐mediated hemolytic anemia (IMHA), thrombocytopenia (ITP), or polyarthropathy (IMPA) occur despite normal hematologic and cytologic parameters. Thymidine kinase 1 (TK1), canine C‐reactive protein (c‐CRP), haptoglobin (HPT), and 25‐Hydroxyvitamin‐D (25(OH)D) might be adjunct to current monitoring strategies. HYPOTHESIS/OBJECTIVES: Compare serum concentrations of TK1, c‐CRP, HPT, and 25(OH)D in dogs with well‐ and poorly controlled primary IMHA, ITP, or IMPA. ANIMALS: Thirty‐eight client‐owned dogs. METHODS: Prospective descriptive study. Dogs diagnosed with IMHA, ITP, or IMPA had serum biomarker concentrations measured commercially. Disease control was assessed by hematocrit/PCV and reticulocyte count, platelet count, and synovial fluid cytology for IMHA, ITP, and IMPA, respectively. Statistical analysis performed by Mann‐Whitney rank‐sum tests and receiver operating characteristic curves. RESULTS: TK1 and c‐CRP, but not HPT significantly decreased with well‐ versus poorly controlled IMHA (P = 0.047, P = 0.028, P = 0.37). C‐CRP, but not TK or HPT was significantly lower with well‐ versus poorly controlled IMPA (P = 0.05, P = 0.28, P = 0.84). Sensitivity and specificity of TK and c‐CRP (simultaneously) for detecting dogs with poorly controlled IMHA were 88 and 100%, respectively. Sensitivity and specificity of c‐CRP for detecting poorly controlled dogs with IMPA were 13 and 100%, respectively. 92% of dogs were vitamin D insufficient (<100 ng/mL) regardless of disease control. CONCLUSIONS AND CLINICAL IMPORTANCE: Combining TK1 and c‐CRP might act markers of disease control in dogs with IMHA. Canine‐CRP cannot be recommended as an independent marker of disease control in IMPA. 25(OH)D insufficiency in immune‐mediated disorders might benefit from further study to determine if supplementation could improve therapeutic response or reduce disease risk.