Page 744 - Small Animal Clinical Nutrition 5th Edition

772 Small Animal Clinical Nutrition

than 0.5 was found in the majority of non-proteinuric dogs induced kidney disease (5/6 reduction of renal mass), mean
VetBooks.ir studied (Grauer et al, 1985; White et al, 1984; Center et al, urine specific gravity was 1.050 ± 0.015 in cats fed a 27.6% pro-
tein food and 1.038 ± 0.013 in a group fed a 51.7% protein food
1985).The upper limit of the reference range for UPC ratios in
(Adams et al, 1994). However, the majority of cats with spon-
cats is 0.2 (Monroe et al, 1989; Adams et al, 1994). However,
in one study of healthy male cats, the 24-hour urinary protein taneously occurring CKD have urine specific gravity values less
loss was greater in males than females and UPC values up to than 1.035 (Polzin et al, 2005). Although it has not been
0.6 were observed.This difference may be attributable to secre- reported, it is generally accepted that urine specific gravity in
tions of secondary sex glands in male cats (Monroe et al, 1989). dogs with naturally occurring CKD is less than 1.030.
Dietary protein intake significantly affected UPC values in
normal cats and cats with surgically induced CKD (Adams et Tubular Resorption
al,1994).Consequently,dietary protein levels should be consid- Water and many solutes are reabsorbed from the tubular lumen
ered when interpreting UPC values because high protein intake into the peritubular interstitial fluid and ultimately the blood.
may increase proteinuria. In general, tubular resorption conserves substances that are
UPC ratios should be performed on all dogs and cats with essential for normal function (e.g., electrolytes, water, glucose
CKD to allow for substaging based on severity of proteinuria and amino acids). Alterations in the renal handling of solutes
(Table 37-1). Studies in dogs and cats with CKD indicate that may indicate kidney dysfunction. Abnormalities in tubular
proteinuria is an important predictor of survival (Syme et al, resorption may be generalized or limited to one or more tubu-
2006; Jepson et al, 2007; Jacob et al, 2005). Cats with UPC val- lar transport processes. Clinical syndromes are defined by the
ues consistently less than 0.2 have significantly longer survival particular transport process involved. These syndromes include
than cats with UPC values greater than 0.4 (Syme et al, 2006; diverse disorders such as nephrogenic diabetes insipidus, renal
Jepson et al, 2007). Similarly, dogs with CKD and UPC values tubular acidosis, renal glucosuria and aminoaciduria (e.g.,
above 1.0 had significantly shorter survival than dogs with cystinuria). Diagnosis is based on urinalysis findings (e.g., cys-
UPC values less than 1.0 (Jacob et al, 2005). Despite correla- tine crystalluria) or other tests such as quantitation of urinary
tion of survival with proteinuria in cats with CKD, there is con- amino acid concentrations.
siderable overlap of survival times across the severity range of
proteinuria. Accurate prediction of survival time for individual Endocrine Function
patients is not possible based on severity of proteinuria (Syme Renal endocrine function can be evaluated by directly measur-
et al, 2006). ing the plasma concentration of the hormone or by indirectly
assessing the action of that hormone. Erythropoietin concen-
Urine Concentration tration can be measured, but it is more practically assessed by
Disorders of urine concentrating ability generally involve serial monitoring of CBCs to detect progressive non-regenera-
abnormalities in the secretion of, or response to, antidiuretic tive anemia that may occur in patients with stages 2 to 4 CKD.
hormone. Loss of concentrating ability can be one of the ear- In CKD, reduced renal excretion of phosphorus causes phos-
liest indicators of kidney dysfunction, which is generally rec- phorus retention, which in turn stimulates increased parathy-
ognized when two-thirds of nephrons are nonfunctional. In roid hormone (PTH) production and secretion. Phosphorus
CKD, the renal interstitial osmolality gradient is decreased retention and hyperphosphatemia also inhibit renal tubular
because of increased urine flow per nephron or because of activity of 1-α hydroxylase, the enzyme responsible for renal
inability to establish and maintain the medullary concentra- conversion of inactive vitamin D to its active form, calcitriol.
tion gradient. The resultant decrease in responsiveness to Decreased calcitriol concentrations, along with hypocalcemia
antidiuretic hormone leads to excretion of urine with osmo- (decreased ionized calcium) and hyperphosphatemia, con-
lality or specific gravity values similar to those of plasma (i.e., tributes to development of hyperparathyroidism. Diagnosis of
isosthenuria). hyperparathyroidism is based on increased plasma concentra-
Estimation of urine concentrating ability from urine specific tions of intact PTH. Although measurement of PTH is not
gravity or refractive index is most often used for clinical purpos- routinely performed for patients with CKD, it should be meas-
es. The physiologic range for urine specific gravity is 1.001 to ured (with serum calcium, phosphorus and ionized calcium)
1.070 in dogs and 1.001 to 1.080 in cats. Any urine specific when calcitriol is administered for management of CKD. In
gravity value may be normal; therefore, it’s important to inter- the future, it may be recommended to monitor serum PTH
pret specific gravity in the context of clinical findings including concentrations in all patients with CKD, before the onset of
hydration status, concurrent disease and medications. (See hyperphosphatemia, so that treatment (e.g., dietary phosphorus
Diagnosis of Chronic Kidney Disease.) In a retrospective series restriction) can be adjusted to control secondary renal hyper-
of cats with CKD, 37% had urine specific gravity values parathyroidism earlier.
between 1.008 to 1.012 and 60% were between 1.013 and
1.034 (Lulich et al, 1992). However, some cats with CKD may Diagnosis of Chronic Kidney Disease
have urine specific gravity values greater than 1.040 and remain Most routine tests used to diagnose CKD do not identify
persistently azotemic (up to 18 months) before losing concen- abnormal findings until there is advanced disease (stage 2 or
trating ability (Polzin et al, 2005). In a study of cats with higher). At present, the most common way to diagnose CKD