Funcion Renal y Manejo Preventivo

Introduction

In older dogs and cats we can find chronic kidney disease (CKD) commonly. However, the time to discover this pathology is often later. The impairment of one or both kidneys that has been present for more than 3 months or the irreversible dysfunction and structural damage, not always shows a clinical signs or pathognomonic finding in structural testing.¹

The kidneys are involved with whole body homeostasis; therefore, the renal failure affects many organ systems, that results in clinical manifestation such as loss of body condition, polyuria and polydipsia (PU/PD), systemic hypertension, anemia, etc.² But not all patients shows clinical or laboratory findings in early stages. Understanding pathophysiology is the key to development of the diagnostic and treatment the renal failure.

In this meeting we can talk to the renal function and discover through the clinical cases, some clues to identify renal failure in early stages, the use of tools to assay the glomerular filtration rate, albuminuria, fractional excretion (FE) of electrolytes and assay of urine biomarkers and his help in a simple clinical practice. Therefore, we can get strategies to prevent the renal damage in older patients covering areas such as feeding, drugs, anesthesia, medical treatment and how to identify of reduced renal functional mass and assist with localization of damage.

Renal Function

The renal system is involved with whole body homeostasis; therefore, in the damage of kidneys, other metabolic disorders occur. Glomerular filtration results in formation of urine in Bowman´s space except for cells and protein-bound compounds. In the proximal tubule occurs there absorption and secretion of anionic and cationic substances. The loop of Henle concentrates then dilutes the filtrate through selective reabsorption of water and sodium. Additionally, to this process, the renal function is involved in metabolic regulation of acid-base status, have endocrine function (e.g., erythropoietin and vitamin D) and have a role in blood pressure regulation. Thus, when renal function declines, results in retention of compounds that should be excreted (creatinine), and loss of compounds that should be retained (e.g., water and protein).²

Prevention of Renal Damage

The renal damage can be caused by acute or chronic insults to the kidney. The most common risk factors for development renal disease are mentioned below.³

 Preexisting renal disease

 Aging

 Fever

 Sepsis

 Trauma

 Diabetes mellitus

 Hypoalbuminemia

 Dehydration

 Cardiac

 Hypotension

 Dietary protein level

 Acidosis

 Electrolytes imbalances

 Nephrotoxic drugs

Always when the patient presents a risk for kidney injury, early detection is the best alliance. The pathological mechanism underlying the severity of kidney disease (KD) are different in dogs and cats. Briefly, in dogs, KD appears to be mediated by glomerulosclerosis and tubulointerstitial damage, whereas in cats, it is predominantly mediated by tubule interstitial, particularly by interstitial fibrosis.⁴

Renal Function Testing

The classic screening test for renal failure includes the creatinine level and impaired urine concentrating ability. However, are relatively insensitive for detecting early kidney injury and do not assist in differentiation between glomerular versus tubular damage. The International Renal Interest Society (IRIS) proposes a guide to classify the stage of renal failure¹ (http://www.iris-kidney.com/pdf/staging-of-ckd.pdf [VIN editor: link modified 6/7/17]). In the creatinine level, systemic blood pressure and proteinuria. However, there are advanced function tests, including glomerular filtration rate, determining fractional excretion of electrolytes, and assay of urine biomarkers, may allow earlier detection of reduced renal functional mass and differentiation of various renal and non-renal differential diagnoses an assist with localization of damage.²

Measurement of glomerular filtration rate allows for precise quantitative assessment of remaining filtration and excretion ability by the kidneys. There are several methods for determination this value in dogs and cats, and several markers have been validated for measurement GFR (creatinine, cystatine, iohexol, and radiolabeled molecules).⁵

The proteinuria with an inactive sediment has long been the clinicopathologic hallmark of chronic kidney disease, the albuminuria, and urine protein:creatinine ratio is the most common test to monitoring the progression of the kidney damage. The other side the urine gama-glutamyl transpeptidasa:creatinine ratio is a new commercial test to improve the chronic kidney disease in early phase.⁶

In cats, the renal disease is a major cause of mortality in the USA close to 50% in geriatric cats.⁷ Sensitive and specific biomarkers for early prediction and monitoring renal failure includes urinary protein and albumin to creatinine ratios, and actually there are studies about the urine proteome.⁷

Symetric dimethylarginine (SMDA) has been shown to be an accurate and a precise biomarker for calculating estimated GFR.⁶ Therefore, is necessary to include in the renal disease monitoring (Figure 1).

Figure 1 Changes in glomerular filtration rate (GFR) are reflected in serum concentration of symmetric dimethylarginine (SDMA) and creatinine (sCr). Factors that increase or decrease GFR, and thus alter serum biomarkers of renal function, are summarized.6

References

1.  Fortney WD. Implementing a successful senior/geriatric health care program for veterinarians, veterinary technicians, and office managers. Vet Clin North Am Small Anim Pract. 2012;42(4):823–834.

2.  Pressler BM. Clinical approach to advanced renal function testing in dogs and cats. Vet Clin North Am Small Anim Pract. Elsevier Inc; 2013;43(6):1193–1208.

3.  Grauer GF. Early detection of renal damage and disease in dogs and cats. Vet Clin North Am Small Anim Pract. 2005;35(3):581–596.

4.  Yabuki A, Mitani S, Sawa M, Mizukami K, Fujiki M, Yamato O. A comparative study of chronic kidney disease in dogs and cats: induction of cyclooxygenases. Res Vet Sci. 2012;93(2):892–897.

5.  Zhou X, Ma B, Lin Z, Qu Z, Huo Y, Wang J, et al. Evaluation of the usefulness of novel biomarkers for drug-induced acute kidney injury in beagle dogs. Toxicol Appl Pharmacol. 2014;280(1):30–35.

6.  Hall JA, Yerramilli M, Obare E, Yerramilli M, Yu S, Jewell DE. Comparison of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in healthy geriatric cats fed reduced protein foods enriched with fish oil, L-carnitine, and medium-chain triglycerides. Vet J. 2014;202(3):588–596.

7.  Ferlizza E, Campos A, Neagu A, Cuoghi A, Bellei E, Monari E, et al. The effect of chronic kidney disease on the urine proteome in the domestic cat (Felis catus). Vet J. 2015;204(1):73–81.