{"id":24842,"date":"2021-12-14T14:26:07","date_gmt":"2021-12-14T14:26:07","guid":{"rendered":"https:\/\/todaysveterinarypractice.com\/?p=24842"},"modified":"2025-10-06T13:03:04","modified_gmt":"2025-10-06T13:03:04","slug":"clinical-approach-to-proteinuria","status":"publish","type":"post","link":"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/urology-renal-medicine\/clinical-approach-to-proteinuria\/","title":{"rendered":"When Urine Trouble: A Clinical Approach to Proteinuria"},"content":{"rendered":"

The clinical significance of proteinuria is evident in dogs with a severe protein-losing nephropathy (PLN<\/a>). Consider Pickles, a 7-year-old male castrated cockapoo that presented for abdominal distention, difficulty breathing, and anorexia (F<\/strong><\/span>IGURE 1<\/span><\/strong>). Pickles was found to have bicavitary effusion and diagnosed with a severe PLN (urine protein:creatinine ratio [UPCR] 28.5, albumin 0.7 g\/dL). Dogs with PLN, such as Pickles, have been shown to have a poor prognosis, with most succumbing to chronic kidney disease (CKD) or thromboembolic complications.1<\/sup><\/span><\/p>\n

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Figure 1. Severe abdominal distention and muscle wasting in a dog with a severe protein-losing nephropathy.<\/p><\/div>\n

Even when concurrent hypoalbuminemia is not present, proteinuria affects the wellbeing of dogs and cats. Proteinuria in dogs is associated with an increased risk of uremic crisis, progressive worsening of azotemia, and death.2,3<\/sup> Similarly, proteinuria in cats with CKD has been shown to be a negative predictor of survival, with one study showing that a UPCR of greater than 0.4 is associated with a 4-fold increased risk of death or euthanasia compared with a UPCR of less than 0.2.4<\/sup> Furthermore, proteinuria may be associated with the development of azotemia in cats. One longitudinal study found that nonazotemic cats with a UPCR of greater than 0.2 were 3.5 times more likely to be azotemic 12\u00a0months later.5<\/sup><\/span><\/p>\n

In addition to promoting progression of kidney disease, persistent proteinuria has several extrarenal consequences, including sodium retention, edema, effusion, hypercholesterolemia, hypertension, hypercoagulability, muscle wasting, and weight loss.1,6,7<\/sup> Therefore, incidental proteinuria on routine diagnostic workups and geriatric screens should not be ignored.\u00a0<\/span><\/span><\/p>\n

The Normal Filtration Barrier<\/h2>\n

Understanding the mechanisms of proteinuria requires a basic understanding of the normal glomerular filtration barrier. Blood comprises circulating proteins that are involved in hemostasis, fluid balance, and transportation. It takes a great deal of energy for the body to make proteins, and loss of these proteins would be wasteful. The glomerular filtration barrier exists to prevent their loss.\u00a0<\/span><\/span><\/p>\n

The glomerulus is a tuft of capillaries that acts as an elegant sieve, allowing waste products to be filtered into the urine while preventing the loss of proteins and blood cells. The glomerulus forms a selective barrier that is best designed to keep albumin, the most abundant circulating protein, from leaking into the urine. As albumin is a 69 kDa negatively charged protein, it makes sense that the glomerular filtration barrier best excludes proteins larger than 65 kDa carrying a negative charge.<\/span><\/p>\n

Blood also contains proteins smaller than 65 kDa, such as retinol-binding protein, a transport protein for vitamin A. These low\u2013molecular weight proteins are freely filtered at the glomerulus but are reabsorbed by proximal tubular cells of the nephron, thereby preventing their loss. However, when there are increased amounts of low\u2013molecular weight proteins in the blood, the proximal tubular cells can become overwhelmed, resulting in proteinuria.<\/span><\/p>\n

Classifying Proteinuria<\/h2>\n

Proteinuria can be broadly classified as prerenal, renal, or postrenal. <\/span>BOX 1<\/span><\/strong> lists conditions that are associated with each type.<\/span><\/p>\n

BOX 1 Classification and Causes of Proteinuria <\/div>
Prerenal<\/strong> <\/span><\/p>\n