SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
Serum levels of Na, K and Cl are often within the normal range in the early stages of
ARF, although hyponatremia and hypochloremia may develop later, particularly if
polyuria or diarrhea exists. Hyperkalemia is unusual with ARF even if the horse is
acidemic.
Analysis of urine
Urinalysis is mandatory before a diagnosis of renal failure can be made. Preferably,
the sample should be obtained before therapy is initiated, although in cases of
prerenal origin this may not always be possible. In severe cases of ARF in which the
animal is profoundly oliguric or anuric, it may be difficult to obtain a useful urine
sample. The existence of azotemia concurrently with an isosothenuric urinary S.G.
is diagnostic of renal failure: these are the preferred tests when ARF is suspected. If
prerenal azotemia exists without specific renal dysfunction, the urine is usually very
concentrated. In such cases, the kidney concentrates the urine in the face of
marked elevations of SUN and Cr concentrations. These perturbations reflect
reduced renal perfusion.
Evaluation of urine for pH, glucose, protein, and blood, as well as sediment analysis
can also be useful. Proteinuria occurs in ARF associated with marked tubular
inflammation or necrosis. It is generally not seen in pre-renal cases unless the
reduced renal perfusion has been of sufficient severity and duration to cause tubular
damage. Glucosuria is generally indicative of proximal tubular dysfunction unless
the animal has been treated with glucose enriched fluids or is markedly
hyperglycemic. Hematuria and hemoglobinuria frequently are seen in ARF, the
former finding varying with the severity and nature of the renal structural damage
while the latter most frequently occurs with diseases having several systemic
abnormalities (e.g. equine infectious anemia, red maple leaf toxicity, immune
mediated hemolytic anemia). Hematuria may occur with renal neoplasia and
abscessation, pyelonephritis, urolithiasis and other lower urinary tract diseases.
Equine urine is normally alkaline (pH 7.5-8.5) and tends to dissolve casts. Therefore
sediment analysis should be performed as soon after collection as possible. Casts
and bacterial and cellular material can be overlooked due to the presence of large
amounts of mucus and CaCO 3 crystals. Alkaline urine can also cause false positive
protein tests when test strips are used.
Calculated indices
Percent Cr clearance rations and the fractional excretion (FE) of electrolytes are
useful in the assessment of equine renal dysfunction. Calculation of these values is
not needed to diagnose renal failure in most animals, unless azotemia is mild and
urine S.G. is not diagnostic. The FE of phosphate increases early in the course of
renal disease, frequently preceding azotemia by several days. Considerable
112