Understanding the SMDA Blood Testing in Cats
Kidney failure, often referred to as renal failure, is a common medical condition in cats. Up to 30% of cats over 15 years old are affected by chronic kidney disease (CKD) which is often the precursor to renal failure.
There are many causes of renal failure and chronic kidney disease over time. Some common causes of CKD and renal failure can include toxins, infections, inflammation of the kidney, kidney or ureter stones (calculi), amyloidosis, neoplasia, hypercalcemia (elevated calcium), various inherited conditions of the kidney, and Polycystic Kidney Disease (PKD). More information can be found in the PetPlace.com library in these articles: Chronic kidney failure in cats and Acute kidney failure in cats.
Chronic kidney disease is a common progressive condition in cats. Early diagnosis and treatment can slow the progression and improve patient quality of life. Early stages of renal disease can be difficult to detect, as your cat may not show any signs until a significant amount of kidney function is lost. Often one of the earliest signs will be increased urination (polyuria) and increased thirst (polydipsia). Dogs will tend to show these signs earlier than cats.
Traditionally, creatinine has been the blood marker that is used in the clinic to monitor renal function. Creatinine does not increase on bloodwork until 75% of renal function is lost! It can also be affected by decreased muscle mass, dehydration, low blood pressure or other causes of decreased cardiac function, and muscle trauma or inflammation.
There is now a new test that will allow your veterinarian to monitor renal function changes much earlier than previously detected. This blood test is called the SDMA (symmetric dimethylarginine assay). This article will explain what we can learn from SDMA monitoring and how this test is run.
What Does SMDA Blood Test Reveal in Cats?
SDMA is made as the body processes protein. It is excreted from the bloodstream through the kidneys if the kidneys aren’t able to filter as well as they should (like in chronic kidney disease or renal failure) the SDMA will increase in the blood. The SDMA value will start to increase when the kidneys have lost 40% of their filtering ability. If you remember from above, creatinine does not increase until 75% of this function is lost. This will now allow veterinarians to recognize chronic kidney disease much earlier in cats and begin to institute treatment and monitoring recommendations based on this information.
Besides early detection, SDMA also has the benefit that it is not affected by lean muscle mass. In aging cats, their muscle mass will decrease and can cause the creatinine to be lowered and difficult to interpret. SDMA is also not affected by some factors that can alter lab machines’ ability to read certain values like lipemia, hemolysis or icterus. It is less affected by dehydration than a BUN, another value on bloodwork that is used to monitor kidney function.
SDMA is not meant to be used as a sole test- the results need to be evaluated in combination with other blood values (BUN, creatinine, and others), urinalysis (especially urine specific gravity and protein level), blood pressure and potentially other tests depending on your cat’s history and clinical picture.
What are the potential uses of SDMA?
An early indicator of renal disease in patients with otherwise normal kidney values (BUN and creatinine)
Better assessment of renal function in patients with severely decreased muscle mass (cachexia)
Aid in differentiating renal versus non-renal causes of elevations in BUN and creatinine
Monitoring during rehydration therapy for patients with elevated BUN and creatinine
Monitoring response to therapy for renal disease over time
How Is SMDA Blood Test Done in Cats?
Your veterinarian and their technical staff will use a needle to obtain a blood sample from your cat, they will usually need 3cc or less (about 1/2 teaspoon) to run the SDMA and other associated tests to evaluate your cat’s kidney function. They will put the sample into specific blood tubes and send it into the laboratory. Depending on the lab used and when it is delivered to them from your veterinarian, you should have the results in 1-2 days.
Is SMDA Blood Test Painful to Cats?
Any pain involved is associated with the collection of the blood sample, since a needle is used to pierce the skin and enter a blood vessel to draw the sample. As with people, the pain experienced from a needle will vary from cat to cat. Often cats resist being held still for the blood draw as much or more than the actual collection itself!
Is Sedation Needed for SMDA Blood Testing?
Neither sedation nor anesthesia is needed in most cats; however, some cats resent needle sticks and may need tranquilization or ultrashort anesthesia.