Uric acid is a substance found in the blood. It gets there when "purines" which are one of the building blocks of your DNA, are broken down. This is normal cell metabolism, and hence it is ok to see some amount of uric acid in the blood. However certain disease conditions, foods, and medications can also raise blood uric acid levels to abnormal levels. High uric acid levels, or "hyperuricemia", may lead to "gout/gouty arthritis", but these terms are not interchangeable.
Chronic Kidney Disease (CKD) is one of the disease conditions that can increase the level of uric acid in your blood. Uric acid level increases usually due to two reasons. Either you are making too much of it (overproduction), or you are not excreting it well enough (underexcretion). Kidney disease is a state where you could have uric acid underexcretion from the kidneys, and hence it is not surprising to see high uric acid levels in patients suffering from CKD.
|Image courtesy of Maggie Smith/ FreeDigitalPhotos.net|
However, the relationship between high uric acid levels and CKD is not that simple. It is in fact a classic chicken-and-egg problem. High uric acid level can itself sometimes cause with kidney disease, although it is uncommon. This entity is called "urate nephropathy". Uric acid stones can also form in the urinary tract when its levels are high in the urine. But in general, although we know that elevated uric acid level is associated with kidney disease, a causal relationship has never been established. This is similar to the situation with other disease entities like hypertension, cardiovascular disease, and diabetes; all of which have been associated with high uric acid levels, but without a conclusive causal relationship. And so, high uric acid level or hyperuricemia, in the absence of any symptoms is, for now, not considered a disease but just a tell-tale lab finding!
SHOULD WE BE TREATING ASYMPTOMATIC HYPERURICEMIA?
This brings us to a common conundrum in the field of nephrology. Do you treat high uric acid levels in patients with kidney disease who otherwise do not have gout or uric acid kidney stones or urate nephropathy (asymptomatic hyperuricemia)? And by doing so, would you necessarily reduce the progression of their kidney disease?
Traditionally, there are a few official recommendations to treat asymptomatic hyperuricemia. These include extremely high uric acid levels (>13 for men, >10 for women, 6 or less in considered optimal), overexcretion of uric acid in the urine (since that can lead to uric acid stone formation), or patients receiving chemotherapy that could increase uric acid levels. In the absence of the above, treatment has usually focused on reducing other risk factors like medications that could increase levels, and putting patients on a low purine diet.
However, we now have a study that might help answer this question. Its results were presented at the American College of Rheumatology meeting in October 2013, in San Diego. This was a retrospective study that showed that patients who are left untreated for a uric acid level over 7 had a 27% higher risk of reduction in their kidney filtration rate (GFR). The study is yet to be published in a peer reviewed journal, but from what I gleaned from the available presentation online, it seems that these patients at baseline did not have symptoms from hyperuricemia that would otherwise mandate treatment per current guidelines (gout, urate nephropathy, etc). On the other hand, patients who took uric acid lowering medications experienced a 37% reduced risk of reduction in their GFR or initiation of dialysis.
Now even though this might not be a perfect study to draw strong conclusions since we are looking at retrospective data, the evidence is still pretty compelling. It makes me wonder if reducing high uric acid levels, even in asymptomatic patients, should be an integral part of management of patients with CKD? Until we have stronger data, it might be worthwhile to discuss this over with your nephrologist.
Veeraish Chauhan, MD, FACP, FASN
Sarasota, Bradenton, FL