Page 950 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Urinary system 925

VetBooks.ir 7.4 Table 7.2 Drugs potentially causing discoloured

urine
Acepromazine Pink to red-brown
Clofazimine Red to orange to brown
Furazolidone Dark yellow to brown
Metronidazole Red to brown
Nitazoxanide Bright orange to dark yellow
Phenazopyridine Red to orange
Rifampin Red to orange

to the urine sample suggests bacterial breakdown of
Fig. 7.4 Normal equine
urine can be quite variable, urea. Diluted urine usually has a neutral to slightly
ranging from clear to turbid. acidic pH.
Proteinuria may occur with pyuria, bacteriuria
and glomerular disease. Physiologically, it can be
Differentiation of pigmenturia is performed by detected after exercise. Glomerular function may
evaluation of the sediment for erythrocytes and by be temporarily altered by stress, fever, seizures,
performing the ammonium sulphate precipitation extreme environmental temperature and venous
test to detect myoglobin. Protein electrophoresis congestion in the kidneys, resulting in reversible
may also be used to differentiate haemoglobin from proteinuria. Commercial reagent strips often yield
myoglobin. Serum samples should be analysed for false-positive results for protein when alkaline urine
concurrent haemolysis. Several drugs may cause dis- is tested or when urine SG exceeds 1.035. Therefore,
colouration of urine (Table 7.2). Discolouration of semi-quantitative sulphosalicylic acid precipitation
urine will be more evident in dehydrated horses. or a colourimetric assay should be used to quan-
A horse with a normal renal function and normal tify the urine protein. Urine protein:creatinine
water intake should concentrate urine to a specific ratio (UP/UC) is helpful in distinguishing primary
gravity (SG) between 1.018 and 1.025 (600–900 glomerular disease (UP/UC >3; usually >5) from pri-
mOsm/kg). In a dehydrated horse, SG may increase mary tubular disease (UP/UC <3).
to or exceed 1.045 (~1500 mOsm/kg). Isosthenuria Normal horse urine should not contain glucose.
may be a sequela of urinary tract or renal disease Hyperglycaemia of different causes (e.g. stress, exer-
or may be physiological and related to water intake. cise, sepsis, pituitary pars intermedia dysfunction
Normal plasma osmolality in adult horses ranges [PPID] or diabetes mellitus) produces glucos-
from 275 to 312 mOsm/kg. Urine osmolality of >300 uria (glycosuria) when blood glucose levels exceed
mOsm/kg indicates the ability of kidneys to concen- 11 mmol/l (200 mg/dl). Dextrose-containing fluids
trate urine and will readily be three to four times or parenteral nutrition compounds may cause glu-
that of plasma. Urine SG should always be measured cosuria subsequent to hyperglycaemia. Similarly,
using a refractometer. The presence of larger mol- alpha-2 adrenergic agonists and treatment with
ecules in urine variably effects SG measurement and corticosteroids may cause glucosuria. Glucosuria
therefore, especially in pathological urine samples, without hyperglycaemia is usually associated with
direct measurement of urine osmolality should be renal tubular dysfunction.
used. Reagent strips are not appropriate. Urine sediment should be evaluated for cells, bac-
Horses usually have alkaline urine with a pH teria, casts and crystals (Figs. 7.5–7.7). Evaluation
between 7.5 and 9.0. Urine may become acidic as a should be carried out no later than 1 hour after urine
result of high-intensity exercise. An ammonia odour collection (Table 7.3).