What the heck is Proteinuria and why is my vet worried? Proteinuria is the presence of abnormally high protein in your pet’s urine. Kidneys function by literally acting as filters of the blood. The filters, called glomeruli are the “microanatomic” structures that are plumbed with small arteries going in and small veins coming out. And each glomerulus is connected to a small “renal tubule” lined by numerous kidney cells. This does not sound that impressive until we consider that each kidney has about 100,000-200,000 glomeruli. As blood swirls around in the glomerulus, blood pressure forces some of the fluid from the blood through small slits and this is the initial urine filtrate/fluid. This initial urine can have some proteins slip into it as well as other substances such as glucose and body salts (electrolytes). The kidney cells lining the “tubules” will then retrieve lost substances that the body wants retained. It’s all pretty complex physiology with many other functions occurring. But as for protein in the urine, most of it is retrieved and ends up back in the blood. So what can go wrong with this system? There are some causes of minor loss of protein through the kidneys to the urine. Lots of exercise or strenuous exercise (that mile run for example), being over heated, high fever, and transient increases of blood pressure are a few common causes of minor protein loss into urine. Occasionally high protein diets can cause extra protein loss into the urine, but this should be minimal and is often overstated. The loss of minor protein amounts may easily be corrected by the changing situation for the body with normal adjustments or rest. If the loss of protein increases to a more easily detected level, it becomes a medical issue and we call this proteinuria. And, proteinuria is a significant concern. Proteinuria can be an only finding on a health check and is first identified with a urinalysis (UA). But proteinuria can also be a factor in several concerning diseases. The usual urinalysis checks for protein with a small “chemistry strip”, using a drop of urine. This is generally pretty accurate for a negative value. But positive results need to be confirmed by additional testing. There are several ways to do this confirmation of excess protein in the urine. However the gold standard currently is a test called a urine protein creatinine ratio (UPCR). This test can have some day to day variability but it is generally a good indicator that a problem of proteinuria is real. Veterinarians often will wait a couple weeks and do a second UPCR test if the first UPCR value or situation does not seem to fit the pet’s health situation. Our medical concerns are proportional to the level of elevation, however even small increases can be a marker of stress or disease to the kidneys. There are a number of risk factors to having a high level of protein in the urine due to kidney disease. And false positives can be present if there is pretty marked inflammatory cells or blood in the urine. But minor infections and minor blood presence will not change the UPCR significantly. Most of the protein lost is albumin as a common “building block” protein found in the serum (fluid portion of the blood). And this is one very important protein for the body. Other similar size proteins can also be lost and affect the pet’s ability to prevent blood clots or to stop bleeding. Another risk with proteinuria is the development of hypertension, which is both a cause or result of proteinuria. There are many health problems that can evolve or link to proteinuria. We worry about inflammation in the kidneys, hypertension, immune system attack on the kidneys, and presence of disease elsewhere in the pet’s body. The last item is important as secondary damage to kidneys (the glomeruli in particular) from disease elsewhere in the body is the most common cause of proteinuria. This “innocent bystander” injury to the kidneys can then become self-progressive. It is also important to recognize that we frequently (40%) cannot find the inciting cause but still are left facing the proteinuria. And as mentioned, proteinuria causes kidney damage as much as it is a result of it. Hence we have a strong desire, as a member of your pet’s health care team, to confirm if proteinuria is present, to look for any causes that we can identify and to start treatment to reduce the proteinuria and protect the kidneys as best that we can. Our medical efforts can have variable success, often stalling or stabilizing the progression. However, we do know that if left untreated, the situation (proteinuria induced kidney disease/failure) will worsen over weeks, months or years. Ask about a routine urinalysis for your pet as part of any general health assessment. Dr. M Hitt August, 2014
Posted on: Mon, 08 Sep 2014 20:03:59 +0000
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