Whether the pet is brought in sick or whether the condition is discovered incidentally on routine lab work, the diagnosis of kidney failure can come as a shock. It does not help that the term kidney failure sounds dramatic and evokes images of on-going sickness, expensive hospitalization, and doom. In fact, the term kidney failure simply means that the kidneys are not able to do at least some of the tasks they are supposed to do as well as they are supposed to do them. Many clinicians prefer the term renal insufficiency or insufficient kidneys so as not to conjure up disturbing images when the patient is in a treatable state. Renal insufficiency is one of those conditions where early intervention can make a big difference and normal life quality can be maintained for months or even years. From a practical standpoint, the terms chronic renal failure, renal insufficiency, chronic kidney failure, and kidney insufficiency all mean the same thing.
Before reviewing what failing kidneys can no longer do, it is important to know what normal kidneys do. Kidney function goes far beyond simply making urine. Kidneys are made of millions of processing units called nephrons. These tiny little processing units are responsible for separating the chemicals you want to keep in your body from the chemicals you need to dispose. The chemicals to remove are dissolved in water and make up the fluid we all know as urine. So here is what your kidneys do for you and your pet, what they become unable to do in renal insufficiency, and some of the parameters your veterinarian will want to track.
Hydration of the body depends not only on water consumed but on water removed. In times of dehydration, the kidney must respond by conserving water. This means that all the materials that the body needs to get rid of still need to removed, but the kidney needs to manage this feat using the smallest amount of water possible. Similarly, if you drink too much water, the kidney needs to efficiently remove the excess to prevent dilution of the blood stream. A pet with insufficient kidney function will not be able to make a concentrated urine and will need to drink extra water to process the body’s waste chemicals. For this reason, excessive water consumption is an important early warning sign and should always be investigated.
When we analyze a urine sample, one of the most important parameters is the specific gravity. It is a measure of how concentrated a urine sample is. Water has a specific gravity of 1.000. A dilute urine sample has a specific gravity less that 1.020 (often less than 1.010). A concentrated urine sample would have a specific gravity over 1.030 or 1.040. A failing kidney by definition cannot make a concentrated urine and the patient must drink excessively to get enough water to excrete the day’s toxic load.
The kidneys remove our metabolic wastes for us. If there is inadequate circulation going through the kidneys or if there are not enough functioning nephrons to handle the waste load, toxins will build up. When they build up and exceed the normal range, a condition called azotemia exists. If the toxins build up to a level where the patient actually feels sick, a condition called uremia exists. If we can keep our azotemic patient below the uremia level, she will feel pretty normal and have good life quality.
The most important marker of uremia is called creatinine, which is a by-product of muscle break-down and is always in the bloodstream in small amounts. The kidney removes it continuously unless there is a kidney function problem. A newer parameter called SDMA (symmetrical dimethylarginine) becomes abnormal much earlier than creatinine and is becoming more commonly tracked. We are able to stage a patient’s kidney disease based on creatinine blood level and SDMA level (see the staging section below). Another marker is BUN, which stands for blood urea nitrogen. This parameter is similar to creatinine but is influenced by dietary protein as well as kidney function. These three markers are central to determining the severity of a kidney problem.
The balance between calcium and phosphorus in the blood is important. Too much of one or the other will lead to crystals forming in the tissues of the body and weakening of the bones to the extent they may actually become rubbery. The kidney plays an important role in this balance and when kidney function is lost, phosphorus levels begin to rise. Therapy for insufficiency kidney function requires monitoring of phosphorus levels and the use of diet and medications to keep phosphorus levels in a reasonable range.
The kidney plays a major role in controlling electrolyte balance as well. In particular, conservation of potassium is an important aspect. Insufficient kidneys lose their ability to conserve potassium and potassium levels begin to drop leading to weakness. Potassium supplements are commonly needed in the treatment of kidney failure.
Blood Pressure Regulation
Blood pressure sensors in the kidney help regulate blood pressure in the body. When these are damaged, hypertension (high blood pressure) can result and can damage the kidney further. Blood pressure is commonly measured in kidney failure patients.
There are a lot of important proteins circulating in the bloodstream and it is crucial that they are not lost in urine. The nephron possesses a filtration system that keeps protein in while removing harmful wastes. If this filtration system is damaged (glomerular disease) then a much more severe form of kidney failure results. Screening for this damage is an important aspect of staging kidney failure and a test called a urine protein:creatinine ratio is often included in the testing profile to assess this condition.
Red Blood Cell Production
The kidney produces a hormone called erythropoietin. This hormone tells the bone marrow to make more red blood cells. In the absence of this hormone, a non-responsive anemia occurs and can get so bad that transfusion is necessary. Erythropoietin can be given by injection to alleviate this problem but there are some potential pitfalls in doing this. Hematocrit and PCV (packed cell volume) are measures of red blood cell volume that are commonly monitored in kidney patients.
Metabolic processes require a narrow pH range for efficiency. The kidney also regulates this balance and if it cannot, intervention is necessary, usually in the form of fluid therapy.
We are born with two kidneys and a huge excess of nephrons. As we live our lives, nephrons die off either as a consequence of disease or simply through wear and tear. When we are down to less than one-third of our kidney’s worth of nephrons (in other words we have lost 5/6 of our total nephrons), test results become notably abnormal and it becomes important to make lifestyle changes. How big these changes are depends on how far things have gone out of whack when the problem is discovered. Early detection of poor kidney function is one of the main reasons laboratory screening tests are recommended.
Staging and Sub-Staging
The International Renal Interest Society (IRIS) has posed the following staging criteria for pets with Stage I being pets with evidence of kidney disease but no evidence of a change in actual kidney function, all the way up to Stage IV where pets begin to feel sick from their disease. These stages are based on blood creatinine levels measured in mg/dl. It is worth noting that MANY patients are well past IRIS Stage IV at the time of diagnosis with creatinine of 8, 9, 12 mg/dl or even higher. IRIS does not have criteria beyond the relatively low creatinine value of 5.0 so it is best to think of the IRIS system as a way to intervene in the earlier stages of renal insufficiency. For patients in more dire initial states, the goal is to drive their toxin levels down to where the IRIS system becomes relevant.
Kidney Failure Treatment in The Houston Heights
At Urban Animal our goal is always to provide your pet with the highest quality care, in a safe and friendly environment. This extends to promoting kidney health through treatment and lifestyle adjustments.