Pearls
- Animals in renal failure frequently have a high anion gap metabolic acidosis due to renal acid retention. Animals with renal disease that are not particularly azotemic can have a normal anion gap metabolic acidosis due to bicarbonate wasting by the kidney.
- Look at phosphorus, urea, and creatinine as a group when interpreting renal function; evaluate these in relation to hydration status and USG.
- Always try to obtain a urine specimen prior to fluid therapy. In chronic renal failure, usually phosphorus, urea and creatinine are elevated in the face of unconcentrated urine.
- Renal function cannot be determined based on the degree of elevation of phosphorus, urea, and creatinine alone. Severely dehydrated animals (prerenal azotemia) may have urea and/or creatinine concentrations much higher than other animals in renal failure.
- There is no “normal” USG. A healthy animal can have a specific gravity ranging from dilute/hyposthenuric to isosthenuric to concentrated depending on hydration status/fluid intake. The definition of “concentrated” urine varies with species. Azotemia together with isosthenuria indicates renal disease, although hypoadrenocorticism is a possible exception (see Chapter 10: Endocrine System).
- Animals can have significant protein-losing nephropathy without being azotemic. Tubular function may be maintained for some time after glomerular disease causes proteinuria and hypoalbuminemia.
- CBC findings that may occur with renal disease:
- Nonregenerative anemia may be present in chronic renal failure and can help distinguish acute from chronic disease.
- An inflammatory leukogram is not seen with lower urinary tract inflammation/infection (e.g. cystitis), but may be seen with pyelonephritis and prostatitis, and is consistently seen with pyometra.
- Cattle with pyelonephritis may have marked hyperfibrinogenemia with or without concurrent leukogram changes
- Electrolyte and acid-base changes often accompany renal disease. Interpret electrolyte changes in relation to the hydration status of the animal. Although hyponatremia may occur due to an inability of the kidneys to reabsorb sodium, it may be masked by volume contraction. Fractional excretion of electrolytes in the urine can be evaluated relative to serum electrolyte levels to determine if solute “wasting” is occurring at the level of the kidney.
- Calcium can be low, high, or within reference limits in renal disease. Hypercalcemia is most frequent in horses and young dogs with renal failure.
definition
Amount of an electrolyte excreted by the kidneys relative to the amount in the glomerular filtrate.
