Page 741 - Small Animal Clinical Nutrition 5th Edition

Chronic Kidney Disease 769

consistent with systemic hypertension (Stiles et al, 1994). Ultrasonography provides information about intrarenal archi-
VetBooks.ir Twelve of the 15 cats (80%) with hypertension had active tecture even when reduced renal function makes excretory urog-
raphy impractical (Walter et al, 1987, 1988). It also can provide
hypertensive retinopathy including increased tortuosity of
images of the kidneys when abdominal effusion or loss of
arteries, retinal edema and focal detachments. In a larger study
of cats with CKD in a primary care practice setting, prevalence abdominal fat reduces radiographic contrast. Ultrasonographic
of hypertension in cats with CKD was about 20% (Syme et al, patterns are not specific for histologic lesions.However,it is pos-
2002). Hypertensive retinopathy has been reported to occur in sible to differentiate solid lesions from fluid-filled lesions and to
dogs with CKD, but it appears to be less common than in cats assess distribution patterns. Ultrasonography also may be used
(Jacob et al, 2003). to detect renal pelvic dilatation secondary to obstruction of the
ureter by ureteroliths or nephroliths.
Routine Laboratory Evaluation Radiography also is useful in the diagnosis of renal osteody-
Most major renal functions can be evaluated diagnostically by strophy. In young dogs with advanced CKD, radiographs of the
routine laboratory tests including complete blood counts skull reveal generalized osteopenia, irregular mineralization and
(CBC), serum biochemistry profiles and urinalyses (Di- dense soft-tissue swelling of the mandibles, maxillae and zygo-
Bartola, 2005). Table 37-4 lists diagnostic tests that are rec- matic arches. The most striking radiographic finding is dem-
ommended for patients with suspected CKD. CBC results are ineralization of lamina dura dentes (i.e., bone surrounding the
useful in dogs and cats with CKD to evaluate the presence of teeth). Radiographs of long bones reveal normal-appearing
anemia and concurrent disorders such inflammation from sys- cortices with a coarse trabecular pattern of the metaphyseal and
temic infection. Azotemia is increased serum urea nitrogen or epiphyseal regions, suggesting demineralization. Spontaneous
creatinine concentrations. Increased serum concentrations of fractures may be evident.The radiographic diagnosis of fibrous
urea nitrogen or creatinine may result from prerenal, renal or osteodystrophy is applied to this constellation of findings.
postrenal disorders. (See Glomerular Filtration and
Localization of Azotemia below.) Results of serum biochem- Blood Pressure Measurement
istry profiles reveal renal azotemia from reduced GFR in Systemic blood pressure varies markedly in healthy pets and
patients in stages 2 to 4 CKD. Dogs and cats with stage 1 may be compounded further by effects of anxiety associated
CKD do not have azotemia. Dogs and cats with CKD have with blood pressure measurement in a hospital environment,
impaired urine concentrating ability and usually have urine and other factors (Bodey and Michell, 1996; Remillard et al,
specific gravity values <1.030 (dogs) or <1.040 (cats), with 1991; Brown et al, 2007). Several studies have evaluated differ-
concurrent clinical dehydration or azotemia. Some cats with ent techniques for measuring blood pressure in dogs and cats.
stage 2 CKD may retain urine concentrating ability (urine In the clinical setting, however, blood pressure is most often
specific gravity values >1.040). However, these patients have measured indirectly (e.g., Doppler ultrasonography, oscillome-
gradually decreasing urine specific gravity values as CKD pro- try). Follow a standard protocol to obtain reliable blood pres-
gresses (e.g., over a period of 18 months) (Polzin et al, 2005). sure values (Table 37-5) (Brown et al, 2007).
Additional notable urinalysis findings may include protein- About 10% of apparently healthy dogs (Remillard et al,
uria (See Altered Membrane Permselectivity below.), gluco- 1991) and 9 to 93% of dogs with CKD are hypertensive
suria from tubular dysfunction or pyuria associated with uri- (Brown et al, 2007); whereas, 19 to 65% of cats with CKD are
nary tract infection. hypertensive (Syme et al, 2002; Brown et al, 2007). Depending
on measurement techniques and methods used to determine
Diagnostic Imaging reference ranges, indirect systolic arterial blood pressures
Radiography and ultrasonography are complementary imag- greater than 141, 160, 170 or 185 mm Hg have been used to
ing modalities that help assess renal structure and localize dis- indicate systemic hypertension. Despite difficulties measuring
ease within the urinary tract (Rivers and Johnston, 1996). blood pressure and confusion regarding diagnostic criteria,
Survey radiographs can assess renal size by comparing the hypertension is a clinically important problem because of its
length of the kidneys with the length of the second lumbar apparent prevalence and potential for associated end-organ
vertebral body on the ventrodorsal view. In a retrospective damage (e.g., retinal hemorrhage and left ventricular hypertro-
series of cats with CKD, 33% had small kidneys, 40% had phy) (Morgan, 1986; Littman, 1994; Elliott et al, 2006a; Brown
kidneys of normal size and 27% had larger than normal kid- et al, 2007).
neys as determined by imaging procedures (Dibartola et al, The IRIS has proposed that dogs and cats with CKD should
1987). Polycystic kidney disease and lymphoma were the be substaged on the basis of risk of hypertensive injury as deter-
most common causes of renomegaly in cats. Feline polycystic mined by serial blood pressure measurements (Table 37-1).
kidney disease can be diagnosed ultrasonographically with a Dogs and cats with CKD with indirect systolic blood pressures
high level of confidence, although extensive polycystic disease less than 150 mm Hg are considered to have minimal risk of
must be differentiated from severe hydronephrosis and perire- hypertensive injury. Patients with CKD and moderate or high
nal pseudocysts (Walter et al, 1988). Excretory urography can risk of hypertensive injury or with overt evidence of hyperten-
be used to qualitatively assess renal function and detect evi- sive injury (e.g., hypertensive retinopathy) should be treated
dence of upper urinary tract obstruction. with appropriate antihypertensive medications.