Uric Acid Kidney Stones

Uric Acid Crystals 

Uric acid crystals are a breakdown product of DNA and RNA in abnormally acidic (low pH) urine. Obese and diabetic individuals, people with gout or kidney disease typically produce abnormally acidic urine. 

In the illustration below, uric acid, the molecule of interest (shown to the far right), has two linked rings made of carbon atoms (represented at the angles where the lines join), with interposed nitrogen (N), oxygen (O), and hydrogren (H) atoms. This molecule has only two charged sites, the nitrogen atoms at the bottom of the rings. 

Uric Acid

In urine of pH of around 6, one nitrogen atom lacks its hydrogen and therefore carries a single negative charge. In more alkaline urine, both nitrogens lack hydrogrens. But, urine does not normally achieve such alkalinity (pH greater than 8). When urine pH is low (less than 5.5) and both nitrogens have their hydrogens, the molecule lacks any charged site, so water cannot find a hold on the molecule. As a result, it crystallizes and simply leaves the water as water droplets themselves (just like those formed high up in the clouds from water vapor that turns to rain).

Water molecules are each a single oxygen atom (large ball in the illustration below) bonded with two hydrogen atoms (small balls pictured below). The hydrogen side has a positive, the bare side of the oxygen has a negative charge. Thus, water molecules link to each other (positives to negative surfaces), to make up the clear continuous fluid that we drink, play in, and hold up umbrellas to keep us dry when it rains. The links occur at the angles where the charges meet (represented by the “1” below”).

Water Molecule

To be considered “in solution,” a molecule must have some charge to which water molecules can link up with by attraction. Calcium atoms are positive and become surrounded by a shell of water molecules facing it with their bare negative surfaces. Oxalic and phosphoric acids have negative charges and are surrounded by water molecules pointing their positives (or hydrogren sides) to them. Uric acid, at neutral pH, has its one negatively charged nitrogen that water can’t grasp. However, when pH falls and neither nitrogen has any extra charge for water to bind with, the molecules stack into solid crystals and fall from solution. 


Uric Acid Stone Formers

Uric acid stones can be orange or red in color. Additionally, they tend to be large and numerous. The red or orange coloration is due to uric acid crystals propensity to absorb hemoglobin breakdown products that are red-orange pigments in urine. At times, Uric Acid crystals pass in urine as red-orange gravel. 

Unlike calcium stones that must bond with either oxalate or phosphate ions to make crystals, uric acid does not have to connect itself to some other atom or molecule to make a crystal. When urine pH is low enough to extinguish its charge, uric acid can crystallize very fast (in seconds), and pass as red-orange gravel in the urine. If retained, such crystals can grow rapidly into large stones. Additionally, because there is more uric acid in urine than there is oxalic acid, Uric Acid stones can grow very large and even more rapidly. Some Uric Acid stones end up filling up the entire collecting system of the kidneys.

Urine pH Controls Stone Formation

Fortunately, because urine pH controls stone formation, Uric Acid stones are very easy to treat. Just a modest amount of alkalizing supplements will make the urine of almost any patient alkaline enough that the hydrogen atoms are removed from the one crucial charged nitrogen. Water can bond at this point so that uric acid remains in solutions. Because of this simplicity, treatments such as supplemental alkali (ex: Stone Relief tea and/or capsules) prevent stones with certainty and relapse need never occur!

Mixed Stones Require Special Care

Unfortunately, stones commonly contain uric acid mixed with calcium oxalate and require special care. In this case, it is suggested that you track down the cause of the Calcium Oxalate stones (almost always diet related- see list of oxalate containing foods HERE) as well as make the urine alkaline enough to stop uric acid stones from forming. Calcium Phosphate crystals mix with uric acid very rarely, because it takes a rather alkaline urine to remove the hydrogren atoms from phosphate (so it has two negative charges and can bind efficiently with calcium atoms). At that high pH, uric acid will have its charge site and remain in solution. 

*Source: Dr. Frederic Coe - University of Chicago


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