Differentiating between acute and chronic kidney disease - Veterinary Medicine
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Differentiating between acute and chronic kidney disease
When dogs and cats have kidney disease, it can be a puzzle determining whether the problem has just developed or has been ongoing. These diagnostics can help you piece the puzzle together to make that distinction so you can provide optimal care and give owners the most accurate prognosis for their pets.



Similar to the serum chemistry profile and CBC, urinalysis is indispensable in diagnosing kidney disease. However, it often does not shed enough light on whether the kidney disease is acute or chronic. An active urine sediment with evidence of pyuria, hematuria, bacteriuria, and proteinuria can be seen with either form of kidney disease. Renal epithelial cells may be present in a urine sample in a patient with AKI. However, it is not possible to definitively distinguish whether the cells originated in the kidney or lower in the urinary tract unless they are formed into casts.45 Occasional renal epithelial cells may be normal. However, larger numbers may indicate acute inflammation, infection, or neoplasia of the renal pelvis.45

Casts may be evident in both AKI and CKD and indicate active damage. Casts rapidly disintegrate, frequently precluding identification at the laboratory.46 Hyaline casts are present with acute or chronic proteinuria and may not represent marked renal pathology.43 Cellular casts are more common in AKI.43 White blood cell casts are usually associated with acute nephritis, pyelonephritis, or toxins that damage the renal tubular epithelium, and red blood cell casts often support a diagnosis of glomerulonephritis or renal hematuria,47 although both types of casts are uncommon in cats and dogs. Casts with kidney tubular epithelial cells signal tubular damage.48 Granular casts can be present in cases of AKI and are composed of cells that have degenerated such that the cell type cannot be distinguished.47 Fatty casts are course granular casts with lipid granules that are seen with glomerular disease or diabetes mellitus.47 Waxy casts indicate chronic renal tubular degeneration47 as they are the final stage of granular cast degeneration.46

Additional laboratory testing: PTH assay

An increased serum phosphorus concentration decreases the serum ionized calcium concentration, which stimulates secretion of PTH to return the ionized calcium concentration to normal. With progressive CKD, PTH concentrations tend to increase. In one study, 47% of asymptomatic cats with CKD had elevated PTH concentrations, compared with 100% of cats with severe end-stage CKD.14 In another study, 100% of dogs with CKD or AKI had elevated PTH concentrations.35 Although the mean PTH concentration was higher in the dogs with CKD compared with those with AKI, this difference was not significant.35


Radiography and ultrasonography can be useful tests in differentiating AKI from CKD as well.

Radiographic examination

An abdominal radiographic examination allows evaluation of renal size and shape. Normal canine kidneys should measure 2.5 to 3.5 times the length of the second lumbar vertebra in a ventrodorsal view.49 The kidneys of neutered cats should measure 1.9 to 2.6 times and the kidneys of intact male and female cats 2.1 to 3.2 times the length of the second lumbar vertebra on a ventrodorsal view.50

Figure 2. Radiographic examination can allow efficient evaluation of kidney size. In this ventrodorsal radiograph of a neutered male cat, the length of the L2 vertebra measures about 2.2 cm. The length of the right kidney measures about 4 cm, and the length of the left kidney measures 6.6 cm. The right kidney is slightly smaller than normal, and the left kidney is enlarged. This radiograph also reveals bilateral nephroliths (arrows) and an irregular margin to the right kidney. Bilateral ureteral obstructions secondary to proximal ureteroliths were diagnosed in this cat. Severe hydronephrosis of the left kidney and mild pelvic dilation were identified with ultrasonography.
Small kidneys in comparison to the patient's size suggest CKD (Figure 2). One study showed 33% of cats with CKD had small kidneys, 40% had normal-sized kidneys, and 27% had enlarged kidneys.51 Renal asymmetry can be caused by chronic damage to one kidney leading to scarring, fibrosis, and small size with hypertrophy of the contralateral side. Acute obstruction of one kidney could lead to enlargement of that side with a normal-sized contralateral kidney, but azotemia would not be expected if the normal-sized kidney were functioning normally. An irregular renal contour can be caused by an acute or chronic infarction, cystic diseases, or, rarely, renal masses. Symmetrically enlarged kidneys suggest acute disease. Uroliths in the kidney or ureters indicate a chronic disease process but may have caused acute uremia from acute obstruction or pyelonephritis. Evaluation of bone density throughout the radiograph is important in diagnosing any concurrent renal osteodystrophy secondary to renal secondary hyperparathyroidism. Radiography alone is 60% sensitive and 100% specific for detecting nephroliths or ureteroliths in cats.52 Ultrasonography alone is 77% to 100%53,54 sensitive and 33% specific,52 and the combination of radiography and ultrasonography is 90% sensitive.55


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