Physiological baseline of conscious tigers: expanded diagnostic framework integrating renal, electrolyte and cardiorenal biomarkers in Panthera tigris

Accurate biochemical reference values for large felids have historically relied on anesthetized or stress-induced sampling, potentially confounding true physiological baselines. This study establishes the first non-anesthetic biochemical reference ranges for tigers (<i>Panthera tigris</i>), defining authentic renal, electrolyte and cardiac parameters under voluntary conscious conditions. Forty captive tigers conditioned for voluntary tail-vein blood withdrawal provided 80 samples without sedation or restraint. Analytes included renal markers (BUN, creatinine, SDMA and uric acid), electrolytes (Na⁺, K⁺ and Cl^-), and cardiac indices (cTnI, NT-proBNP and CK-MB). Mean ± SD values were: BUN 15 ± 2 mg/dL, creatinine 1.2 ± 0.1 mg/dL, SDMA 8.0 ± 0.5 μg/dL, uric acid 4.5 ± 0.6 mg/dL, Na⁺ 151 ± 2 mEq/L, K⁺ 4.6 ± 0.4 mEq/L, Cl^- 111 ± 3 mEq/L, cTnI 0.02 ± 0.01 ng/mL, NT-proBNP 200 ± 25 pg./mL, and CK-MB 7.5 ± 1 U/L. Strong BUN-creatinine (r = 0.82 <i>p</i> < 0.001) and SDMA-creatinine (r = 0.80 <i>p</i> < 0.001) correlations confirmed synchronized glomerular filtration, while Na⁺-Cl^- coupling (r = 0.92 <i>p</i> < 0.001) validated ionic balance. Cardiac indices exhibited low variability (CV < 10%) and a moderate SDMA-NT-proBNP relationship (r = 0.46 <i>p</i> < 0.01) demonstrated a functional cardiorenal continuum. Using voluntary sampling, this study defines the first physiologically valid biochemical and cardiorenal reference baselines for tigers supporting improved welfare, greater diagnostic reliability and earlier identification of renal and cardiac pathology in managed large felids.