The Complete Blood Count (CBC) is an overview of what is running through our pets veins: Red Blood Cells, White Blood Cells and Platelets. The Chemistry Panel offers insight into how different organ systems are functioning. We have markers that help to evaluate liver, kidney, gastrointestinal tract and even endocrine function. While all organs are of importance and their proper function is essential to your pet’s health and longevity, let’s focus on a pair of very important organs for now…the kidneys!
The kidneys serve as a target organ for many hormones in the body (Aldosterone, Parathyroid Hormone and Antidiuretic Hormone) as well as functioning to metabolize and secrete various hormones (like Insulin, Erythropoietin and Prostaglandins). The kidneys' primary function are to play an essential role in maintaining a healthy balance within the body by regulating the water and electrolyte balance. This is achieved by filtering the blood to excrete toxic waste products and preserve fluids. In order to do this, the kidneys receive about 25% of the TOTAL cardiac output. In other words, a quarter of all of the circulating blood pumped through the heart is dedicated to the kidneys.
In order to filter and excrete nitrogenous waste, there needs to be a filtration rate that is maintained by around 20% of the plasma flowing through the kidneys. This filtration rate is called the Glomerular Filtration Rate or GFR - you may have seen this value reported on your very own blood results from your own physician! This filtration is maintained by the body’s blood pressure which needs to be maintained between 60 to 160 mmHg to minimize the risk of organ damage. It makes sense that our physicians monitor our blood pressure and why they become so concerned with elevated pressures. Unfortunately, monitoring routine blood pressures in our dogs and cats is not so easily performed. When your pet’s kidneys aren’t functioning properly, these declines in renal function can lead to soft-tissue mineralization, systemic hypertension and protein loss in the urine. This is why evaluation of renal function becomes so important if we want to be able to improve clinical outcomes for dogs and cats.
It is estimated that as many as 30-50% of cats 15 years of age or older have Chronic Kidney Disease. Clinical signs suggestive of Chronic Kidney Disease include: increased thirst, increased urination, weight loss and poor appetite. It is important to note that these clinical signs of kidney disease occur only after 70% of the cells essential in renal function have died and at this point there is only minimal supportive therapy that can be offered to attempt to maintain quality and quantity of life. Since clinical signs don’t develop until such an advanced and dangerous stage in renal malfunction, a combination of tests are used to evaluate GFR and the kidneys’ filtration ability. When assessing the Chemistry Panel, Blood Urea Nitrogen (BUN) and Creatinine have traditionally been the only two serum tests used to evaluate renal function, until recently. Now, along with BUN and Creatinine, there is a new marker of renal function called Symmetric Dimethylarginine or SDMA through our reference laboratory (IDEXX Laboratories).
Unfortunately, there is no single test available to diagnose renal malfunction and there are limits to the combination of BUN and Creatinine. BUN levels vary widely depending on the pet’s hydration status, protein consumption in the diet and other variables not related to kidney function. And while serum Creatinine levels are a more specific indicator of GFR, since Creatinine is produced by break-down of skeletal muscle, muscle mass will influence and skew the Creatinine levels meant to reflect GFR. For example, if a dog or cat starts losing muscle mass as he/she ages, this can lower the Creatinine levels within the body, masking real elevations in Creatinine due to poor filtration through the kidneys. For this reason we also need to assess Urine Specific Gravity (whether your pet’s urine is concentrated or dilute in nature) and our physical exam findings to piece together possible kidney malfunction that may have been occurring for years.
This newer test, SDMA, on the other hand is NOT affected by muscle mass or other non-kidney related causes of blood work variations. This makes SDMA a more specific screening tool for renal function in dogs and cats. Serum SDMA is derived from the breakdown of intra-nuclear proteins produced by every cell in the body and is excreted almost exclusively by the kidneys. Studies have shown that SDMA concentrations increased and indicated abnormality in renal function about 17 months sooner than serum Creatinine levels!
Studies have shown that SDMA is a sensitive biomarker for earlier detection of kidneys disease than what was previously possible. That is why IDEXX Laboratories (the reference laboratory regularly used by T.A.H. for special testing) is now including SDMA in all of their Chemistry Panels. When kidney disease is suspected in your pet, submitting a blood sample to IDEXX for this new and beneficial marker is now recommended and is used in conjunction with BUN and Creatinine to give a better clinical picture of health. SDMA now allows the doctors at T.A.H. to detect kidney dysfunction months and possibly years earlier,
which will allow for earlier medical intervention in the hope that we will be able to improve outcomes and save lives.
Learn more about IDEXX and the new SDMA test, and also watch an informational video, by clicking here!