Serum creatinine is derived from muscle creatine at a relatively constant daily rate, and is not as affected by non-renal factors as serum urea. Serum creatinine is excreted almost exclusively through renal glomerular filtration. Patients may experience significant reduction in functional nephron number and GFR (>75%) before serum creatinine is significantly increased. Reductions in GFR from prerenal, renal, or postrenal causes cannot be distinguished as all may increase serum creatinine. Postrenal causes (e.g. lower urinary tract obstruction) are usually associated with the largest and fastest increases. Decreased serum creatinine results are rarely clinically significant, though animals with lower muscle mass tend to have lower baseline serum creatinine. Serum creatinine tends to parallel serum urea in renal disease or reduced renal perfusion.
Major differentials fro increased serum creatinine include reduced renal perfusion (dehydration, shock, cardiovascular disease), urinary tract obstruction or rupture, and renal disease. Results should be interpreted in conjunction with urinalysis.
All species (however, serum creatinine is not very useful in birds/reptiles)
Plasma or Serum
Gel, plain or heparin tube
Fasted sample preferred.
Reference(s): Stockham, S.L and Scott, M.A. Fundamentals of Veterinary Clinical Pathology 2nd Edition 2008. Thrall M.A. Veterinary Hematology and Clinical Chemistry 2006