Why then scruple over percentages? If I find uric acid in any stone, I look at urine pH with a yellow eye. Should it be low I treat it surely and on the moment so at least that crystal be banished forever. The Profligate Punished by Neglect, Edward Penny catches the common motif of diet excess, obesity, diabetes, and gout — the joint manifestations of uric acid crystals.
Note the abdominal fat denoted by his overly tight vest. All of these states can lower urine pH and lead to uric acid stones. This article has a pragmatic leaning and eschews excessive scientific details. I have written a more mechanistic article that explores how the low urine pH might arise and cause uric acid stones. Read this one first unless you are already reasonably expert. Given my prior reasoning, I call patients who have any uric acid in their stones uric acid stone formers but reserve the right to use compound names when needed.
If all stones are only uric acid, I call such patients pure uric acid stone formers. These niceties of naming have the practical value of calling to mind the perpetual need for dual or multiple treatments — for uric acid but also for whatever crystals might be present.
Commonly uric acid stones show poorly on routine flat plate x rays having only carbon, nitrogen, oxygen and no heavier atoms such as calcium. On CT scans they do not look different from calcium stones but radiographic density can be measured and tends to be lower. As this article points out, machines differ in their results and evaluation may therefore be less than perfect. Dual energy scanners are more precise, but also prone to many potential artefacts.
Multiple reports, by contrast, indicate that CT measurements of radiographic density can reliably distinguish uric acid stones from calcium stones. A reasonable present view is that lower radiographic density is an excellent clue to uric acid in stones, but far from definitive as stone analysis is.
I hesitate to classify a patient on scanning evidence alone. Being stones, uric acid stones cause the usual problems of pain, obstruction, bleeding and infection. But they have some special features. The most obvious is stone color — red to orange because the crystals take up a variety of pigments mostly derived from hemoglobin breakdown. Recently scientists have determined the structure of one of these — urorosein. Sometimes, coarse or fine orange or red gravel passes, made up of uric acid crystals.
Because the crystals form not as a complex lattice like calcium with oxalate or with phosphate but simply as uric acid crystallizing with itself, the process can be swift to begin and require very little supersaturation.
Said more technically the energy required to create the crystal is relatively low. This means the upper limit of metastability — the supersaturation needed to initiate crystal formation is not far from solubility, so values above 1 even if below 2, could suffice.
Practically it means that bursts of supersaturation during the day can bring on showers of gravel and growth of stones. Also, urine contains a lot of uric acid. Common daily losses of oxalate approximate perhaps 25 — 50 mg, compared to — 1, mg of uric acid. The sheer amounts available when coupled to the rapid and facile crystal formation and growth allow stones to enlarge rapidly and achieve very large sizes, enough to fill the renal pelvis and calyces — so called staghorn stones.
Very uncommonly, sudden lowering of urine pH coupled with low urine volume can cause crystallizations in the terminal collecting ducts with acute kidney failure. This was once not uncommon during treatment of malignancies, but modern attention to uric acid surges from tumor killing has made it rare indeed.
Today, one does not expect to see it apart from unusual situations. I made the figures for this section anew but from a lovely data file constructed some years ago by Joan Parks , who was my scientific colleague from until her retirement about 8 years ago. Her legacy of curated data files sustains a lot of my public writing, now, and she deserves a place in it.
Uric acid crystals form like all crystals because of supersaturation. In this instance, that supersaturation varies remarkably with urine pH. In the figure, supersaturation ranges from 0. The dashed line at 1 represents equilibrium, or saturation, the level where crystals neither form nor dissolve. The horizontal axis shows urine pH. The dashed lines at 5. The tiny points each are one 24 hour urine from patients and normal people. Like an ancient Persian scimitar, points curve downward from 8 to 0.
Urine volume matters. Low volumes red 0. But pH trumps volume. At pH 5. Below 5. In speaking about excretion of uric acid we need to insert a note about the molecular species involved.
Uric acid is a weak acid, which means it can take up or donate a proton to water. When it has its proton, that proton neutralizes much of its charge , so water molecules cannot themselves form charge bonds with it to keep it in solution.
This means that the molecule becomes very poorly soluble and tends to crystallize. When it loses its proton into solution, it has a charged site for water to relate to and also requires a counterion, which in urine will be sodium, potassium, and ammonium ion.
But all three salts have much higher solubility than uric acid itself. When we measure and report urine uric acid excretion we show the sum of all salts and the acid in one number. Obviously this total should affect supersaturation, but the effect is relatively small because so much depends on pH that sets the percentage of uric acid per se — the fraction that has its proton and is therefore poorly soluble.
One presumes that urine pH of uric acid stone formers must lie below that of other kinds of stone formers, and numerous reviews and case descriptions have proven this true. The dot distribution just below shows individual 24 hour urine pH measurements for calcium oxalate blue , calcium phosphate green and uric acid red stone formers.
Here I include among uric acid stone formers those with both pure and mixed stones. Calcium oxalate stone former pH ranges widely with an average at about 5. Calcium phosphate stone formers average a lot higher — around 6. Uric acid stone formers lie in an acid range.
Their average is about 5. So uric acid stone formers produce a very acid urine compared to other stone formers, and the pH is exactly in the range to produce supersaturation that can drive formation of uric acid stones and hold them steady or cause them to grow.
To see this, just look back on the graphs showing supersaturation vs. I have said that any uric acid in stones means pH should be raised because at least that portion of the stone burden might dissolve or at leasts not grow.
The figure below shows urine pH associated not with the kind of patient — calcium oxalate, calcium phosphate or uric acid stone former, but by the fraction of a given stone made up of uric acid. Blue means no uric acid at all. With a scattered few points as exceptions, stones made of mainly uric acid go with urine pH values mostly below 5. The graph makes a point we often speak of but rarely show.
Oxalic acid has a very low pKa — is a strong weak acid. So it has charges available for binding to calcium that very hardly at all with urine pH all the way down to 4. So these stone crystals are indifferent to pH. I makes another point, too, one that a patient emphasized in a comment to this article and that I failed to mention in the original version.
Of all stones that contain any uric acid, at least in my collection of data, most are mainly composed of uric acid. See where the red — pure uric acid — stones make up the largest mass in the figure just above? Cleveland Clinic.
December 30, Ueno S, et al. Drug Research. December Uric Acid Stones. November 3, CreakyJoints is a digital community for millions of arthritis patients and caregivers worldwide who seek education, support, advocacy, and patient-centered research. We present patients through our popular social media channels, our website CreakyJoints. We represent patients through our popular social media channels, our website CreakyJoints.
Only fill in if you are not human. These symptoms could point to any of the four types of kidney stones, which are classified based on what they are made of: Calcium Struvite from bacteria Cystine from an amino acid Uric acid That said, there are no symptoms that indicate you are experiencing uric acid stones specifically due to gout.
Treatment for Gout-Related Kidney Stones Treatment for kidney stones includes getting rid of, or passing, stones you currently have and preventing future stones from developing. Lifestyle Changes Here are other important lifestyle changes he recommends: 1. Watch what you eat Avoid eating too many foods high in purines , which the body breaks down into uric acid.
Stay hydrated A person with a history of kidney stones should focus on staying hydrated to maintain optimal kidney function. Medications Medication to lower uric acid levels is a key part of treating gout, and in turn, reducing the risk of gout-related kidney stones. If, however, you have decreased kidney function, NSAIDs may increase your risk of sudden kidney failure and potentially progressive kidney damage, according to the National Kidney Foundation.
Alpha blockers, a type of blood pressure medication, may be prescribed to help patients pass kidney stones. But a study found that alpha blockers may increase the level of uric acid in patients.
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Share on: Facebook Twitter. Show references Goldman L, et al. In: Goldman-Cecil Medicine. Accessed Jan. Kidney stones. McKean SC, et al. In: Principles and Practice of Hospital Medicine. McGraw-Hill Education; What are kidney stones?
American Urological Association. Kellerman RD, et al. In: Conn's Current Therapy Elsevier; Warner KJ. Allscripts EPSi. Mayo Clinic. Curhan GC, et al. Diagnosis and acute management of suspected nephrolithiasis in adults. A dietitian can help you plan meals to help you lose weight. Follow a healthy diet plan that has mostly vegetables and fruits, whole grains, and low-fat dairy products. Limit sugar-sweetened foods and drinks, especially those that have high fructose corn syrup.
Limit alcohol because it can increase uric acid levels in the blood and avoid short term diets for the same reason. Decreasing animal-based protein and eating more fruits and vegetables will help decrease urine acidity and this may help reduce the chance for uric acid stone formation. Citrate might be prescribed to help prevent certain stones, such as uric acid stones, if urine citrate is low and urine pH levels are too low or too acidic.
Citrus juices do contain citrate citric acid , but large amounts might be needed. Also, be careful of sugar. Lemon juice concentrate 4 oz per day mixed with water can be considered. Alkali citrate can be prescribed such as potassium citrate and is available over-the-counter. Alkali citrate can be given with a mineral s , such as sodium, potassium or magnesium to help prevent stone formation. The aim is to increase urine citrate for prevention of calcium stones and increase urine pH or make urine less acidic or more alkaline, for prevention of uric acid and cystine stones.
The goal is to keep pH in balance. Speak with a doctor or other healthcare professional about which treatment options are right for you, including over-the-counter products and home remedies.
This may not apply to all types of stones, so speaking with a healthcare professional is important. People with kidney disease may need to watch their intake of sodium, potassium or other minerals, depending on the stage of kidney disease or other factors. Diagnosis of a kidney stone starts with a medical history, physical examination, imaging tests, urine and blood testing, and stone analysis.
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