Editorials • J. Bras. Nefrol. 40 (1) • Jan-Mar2018 • https://doi.org/10.1590/1678-4685-JBN-2018-00010002 copy
Mauricio Carvalho Correspondence to: Mauricio Carvalho. E-mail: m_carvalho@hotmail.comUniversidade Federal do Paraná, Departamento de Clínica Médica, Hospital de Clínicas, Curitiba, PR, Brasil.Pontifícia Universidade Católica do Paraná, Escola de Medicina, Curitiba, PR, Brasil.
About the author
Urinary pH is a major determinant for kidney stone formation. Supersaturation of calcium phosphate increases rapidly as urine pH rises above 6. The prevalence of calcium phosphate stones has increased recently and urinary conditions that favor the formation of these stones are the combination of hypercalciuria and hypocitraturia in alkaline urine. Some patients may have complete or incomplete distal renal tubular acidosis (dRTA) characterized by hyperchloremic acidosis (incomplete dRTA does not manifest metabolic acidosis under basal conditions), hypocitraturia, and high urine pH. The use of carbonic anhydrase inhibitors such as acetazolamide and topiramate leads to a similar scenario.11 Goldfarb DS. A woman with recurrent calcium phosphate kidney stones. Clin J Am Soc Nephrol 2012;7:1172-8.
A low urine pH is the most important factor leading to uric acid stone formation. Uric acid is a weak organic acid with a pKa of 5.5. At such low pH, soluble uric acid crystallizes. Quantitatively, with urine pH of 5.3 and urate excretion of 800 mg/day, precipitation of uric acid would likely occur with a daily urine volume that is as high as two liters.22 Kamel KS, Cheema-Dhadli S, Halperin ML. Studies on the pathophysiology of the low urine pH in patients with uric acid stones. Kidney Int 2002;61:988-94. In obese patients, because of hyperinsulinemia and insulin resistance related to visceral obesity, dysfunction in ammonium excretion and urine acidification in the proximal tubule cause low urinary pH.33 Maalouf NM, Cameron MA, Moe OW, Sakhaee K. Metabolic basis for low urine pH in type 2 diabetes. Clin J Am Soc Nephrol 2010;5:1277-81. In fact, in recent years, kidney stone formers present with high BMI (overweight or obesity), increased waist circumference, and high body fat percentage. These findings might be associated with increased calcium, oxalate, and uric acid excretion, thus increasing the risk of kidney stone formation.44 Oliveira LM, Hauschild DB, Leite Cde M, Baptista DR, Carvalho M. Adequate dietary intake and nutritional status in patients with nephrolithiasis: new targets and objectives. J Ren Nutr 2014;24:417-22.
It is well known that most calcium stones are composed primarily of calcium oxalate (~80%). The role of urine pH in the formation of calcium oxalate stones is highly controversial. Most authors found that calcium oxalate stones could form in any urine pH. The benefit of increasing urine pH in calcium oxalate stone formers with low urine pH and normal urinary citrate is uncertain.
In a study published in this issue of BJN, Tessaro et al. analyzed the influence of nutritional status, laboratorial parameters, and dietary patterns on urinary acid excretion in calcium stone formers. They concluded that the endogenous production of organic acids and not an acidogenic diet was an independent predictor factor for lower urinary pH levels in calcium stone formers.55 Tessaro CZW, Ramos CI, Heilberg IP. Influence of nutritional status, laboratorial parameters and dietary patterns upon urinary acid excretion in calcium stone formers. Braz J Nephrol 2018;40. In press. In addition, hypercalciuric and/or hyperuricosuric patients presented higher organic acid levels and lower urinary pH.
Despite the limitations of a retrospective study and the lack of measurement of some urinary components (like sulfate, a direct marker of acid intake, or ammonium), the study brings to light several questions. Theoretically, a low urinary pH can be caused by increased base loss, increased acid intake (high consumption of animal protein), increased endogenous acid production, and decreased urinary ammonium. If increased endogenous acid production is the cause for the lower urinary pH found in hypercalciuric stone formers as reported here, the pertinent questions are: 1) what is the mechanism? 2) Is it clinically relevant?
Insulin resistance and obesity are associated with increased endogenous acid production and may be the most obvious explanation. However, is it possible that urinary calcium per se can stimulate urinary acidification? Double KO mice lacking the TRPV5 calcium channel (the major pathway for transcellular calcium reabsorption in the late distal tubule) and B1 H+-ATPase subunit (part of the cytosolic H+-ATPase pump from intercalated cells and required for maximal urinary acidification) present with massive increase in calciuria and phosphaturia and more alkaline urine than wild-type mice. The result is massive hydronephrosis and kidney stones.66 Renkema KY, Velic A, Dijkman HB, Verkaart S, van der Kemp AW, Nowik M, et al. The calcium-sensing receptor promotes urinary acidification to prevent nephrolithiasis. J Am Soc Nephrol 2009;20:1705-13. Defensive mechanisms may protect from kidney stone formation in conditions such as hypercalciuria where high luminal calcium concentrations stimulate urinary acidification and reduce urinary concentration via a calcium-sensing receptor, resulting in the excretion of acidic and diluted urine.77 Wagner CA, Mohebbi N. Urinary pH and stone formation. J Nephrol 2010;23:S165-9. Whether these protective mechanisms can be translated from mice to humans is uncertain.88 Worcester EM, Coe FL. Does idiopathic hypercalciuria trigger calcium-sensing receptor-mediated protection from urinary supersaturation? J Am Soc Nephrol 2009;20:1657-9.
Finally, there is almost a consensus that calcium oxalate supersaturation is independent of urine pH. Nonetheless, a recently experimental work revealed that CaOx monohydrate was crystallized with greatest size, number, and total mass at pH 4.0 and least crystallized at pH 8.0. Fourier-transform infrared (FT-IR) spectroscopy confirmed the morphological study. Moreover, the crystal-cell adhesion assay showed highest crystal-cell adhesion at the most acidic pH.99 Manissorn J, Fong-Ngern K, Peerapen P, Thongboonkerd V. Systematic evaluation for effects of urine pH on calcium oxalate crystallization, crystal-cell adhesion and internalization into renal tubular cells. Sci Rep 2017;7:1798. Unquestionably, further studies with large clinical databases providing population characteristics, identifying risk factors, and developing prognostic models are necessary to confirm the clinical relevance of these findings.1010 Cook JA, Collins GS. The rise of big clinical databases. Br J Surg 2015;102:e93-e101.
- 1
Goldfarb DS. A woman with recurrent calcium phosphate kidney stones. Clin J Am Soc Nephrol 2012;7:1172-8.
- 2
Kamel KS, Cheema-Dhadli S, Halperin ML. Studies on the pathophysiology of the low urine pH in patients with uric acid stones. Kidney Int 2002;61:988-94.
- 3
Maalouf NM, Cameron MA, Moe OW, Sakhaee K. Metabolic basis for low urine pH in type 2 diabetes. Clin J Am Soc Nephrol 2010;5:1277-81.
- 4
Oliveira LM, Hauschild DB, Leite Cde M, Baptista DR, Carvalho M. Adequate dietary intake and nutritional status in patients with nephrolithiasis: new targets and objectives. J Ren Nutr 2014;24:417-22.
(Video) The 5 Worst Foods for Calcium Oxalate Kidney Stones | How to Prevent Getting Kidney Stones (2020) - 5
Tessaro CZW, Ramos CI, Heilberg IP. Influence of nutritional status, laboratorial parameters and dietary patterns upon urinary acid excretion in calcium stone formers. Braz J Nephrol 2018;40. In press.
- 6
Renkema KY, Velic A, Dijkman HB, Verkaart S, van der Kemp AW, Nowik M, et al. The calcium-sensing receptor promotes urinary acidification to prevent nephrolithiasis. J Am Soc Nephrol 2009;20:1705-13.
- 7
Wagner CA, Mohebbi N. Urinary pH and stone formation. J Nephrol 2010;23:S165-9.
- 8
Worcester EM, Coe FL. Does idiopathic hypercalciuria trigger calcium-sensing receptor-mediated protection from urinary supersaturation? J Am Soc Nephrol 2009;20:1657-9.
- 9
Manissorn J, Fong-Ngern K, Peerapen P, Thongboonkerd V. Systematic evaluation for effects of urine pH on calcium oxalate crystallization, crystal-cell adhesion and internalization into renal tubular cells. Sci Rep 2017;7:1798.
- 10
Cook JA, Collins GS. The rise of big clinical databases. Br J Surg 2015;102:e93-e101.
- Publication in this collection
09Apr2018 - Date of issue
Jan-Mar2018
About the author
Mauricio Carvalho
Universidade Federal do Paraná, Departamento de Clínica Médica, Hospital de Clínicas, Curitiba, PR, Brasil.
Pontifícia Universidade Católica do Paraná, Escola de Medicina, Curitiba, PR, Brasil.
Correspondence to: Mauricio Carvalho. E-mail: m_carvalho@hotmail.com
How to cite
FAQs
How does urine pH affect stone formation? ›
The formation of various types of kidney stones is strongly influenced by urinary pH. An alkaline pH favors the crystallization of calcium- and phosphate-containing stones, whereas and acidic urine pH promotes uric acid or cystine stones.
What pH do calcium oxalate stones form? ›The risk of calcium oxalate (CaOx) crystallization at different pH levels was determined in urine from recurrent CaOx-stone formers and normal subjects. The highest crystallization risk was observed between pH 4.5 and 5.5.
What should urine pH be to prevent kidney stones? ›Maintain a neutral urine pH. A balanced pH (closer to 7) is key to battling stones.
Why does urine pH matter? ›A urine pH test measures the level of acid in urine. Some types of kidney stones are more prone to develop in alkaline urine and others are more likely to from in acidic urine. Monitoring the urine pH may be helpful in preventing the formation of kidney stones.
Do calcium oxalate stones form in acidic urine? ›Most authors found that calcium oxalate stones could form in any urine pH. The benefit of increasing urine pH in calcium oxalate stone formers with low urine pH and normal urinary citrate is uncertain.
What is ideal urine pH? ›The American Association for Clinical Chemistry says the normal urine pH range is between 4.5 and 8. Any pH higher than 8 is basic or alkaline, and any under 6 is acidic. A urine pH test is carried out as a part of a urinalysis.
What is normal pH of urine? ›Normal Results
The normal values range from pH 4.6 to 8.0.
Calcium oxalate
They're colorless and can be found in healthy urine. Calcium oxalate crystals are heavily associated with kidney stones, which can form when too much oxalate (found in such foods as spinach) is in the system.
Both uric acid and cystine stones can be dissolved if the urine is made alkaline (pH 6-7).
What foods to avoid if you have calcium oxalate kidney stones? ›- nuts and nut products.
- peanuts—which are legumes, not nuts, and are high in oxalate.
- rhubarb.
- spinach.
- wheat bran.
What does high pH mean? ›
pH is a measure of how acidic/basic water is. The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base.
What does a urine pH of 5.0 mean? ›Urine pH typically is 5 as a result of daily net acid excretion. An alkaline pH often is noted after meals, when an “alkaline tide” to balance gastric acid excretion increases urine pH. A high urine pH also is seen in patients who are on a vegetarian diet.
Is it better to have acidic or alkaline urine? ›For example, urine with a lower pH (more acidic) tends to inhibit the growth of bacteria, and urine that is high in ammonia (more alkaline or basic) may impede the body's immune response to a urinary tract infection.
What factors affect urine pH? ›Diet, certain drugs, infections, and poor kidney function can all affect the pH of urine. For example, diets high in protein from meat, fish, dairy, and grains can decrease urine pH (more acidic), whereas diets high in fruits and vegetables can increase urine pH (more alkaline) [6, 7, 8].
How can I lower calcium in my urine naturally? ›To lower the calcium level in your urine, your healthcare provider might suggest that you eat more vegetables and fruits and less animal products, like red meat and eggs. If you're an older adult, your provider may recommend that you add more potassium and reduce the amount of salty foods in your diet.
What will dissolve calcium oxalate kidney stones? ›Citrate, not phosphate, can dissolve calcium oxalate monohydrate crystals and detach these crystals from renal tubular cells.
What drink good for kidney stones? ›- Staying hydrated is key. Drinking plenty of fluids is a vital part of passing kidney stones and preventing new stones from forming. ...
- Water. When passing a stone, upping your water intake can help speed up the process. ...
- Lemon juice. ...
- Basil juice. ...
- Apple cider vinegar. ...
- Celery juice. ...
- Pomegranate juice. ...
- Kidney bean broth.
Acidic urine can also create an environment where kidney stones can form. If a person has low urine pH, meaning that it is more acidic, it might indicate a medical condition, such as: diabetic ketoacidosis, which is a complication of diabetes. diarrhea. starvation.
Is calcium oxalate basic or acidic? ›Calcium oxalate is a combination of calcium ions and the conjugate base of oxalic acid, the oxalate anion. Its aqueous solutions are slightly basic because of the basicity of the oxalate ion.
Is calcium oxalate acidic or alkaline? ›Calcium oxalate develops in acidic urine (pH less than 6.0). Calcium phosphate develops in alkaline urine (pH greater than 7.5).
What does a pH level of 7 mean? ›
A measure of how acidic or basic a substance or solution is. pH is measured on a scale of 0 to 14. On this scale, a pH value of 7 is neutral, which means it is neither acidic nor basic. A pH value of less than 7 means it is more acidic, and a pH value of more than 7 means it is more basic.
What do I do if my urine is too alkaline? ›If the urine test shows too much alkaline or too much acid, the first step to usually correct the problem is to increase your water intake. If you are not on fluid restrictions by your physician, you should drink six-to-eight, 8 oz glasses of water daily.
Can dehydration cause high pH in urine? ›A highly acidic urine pH occurs in:
Starvation and dehydration.
High pH levels occur when hydroxide ion concentrations are high and hydrogen ions are scarce. Although acidic conditions more commonly result from human activities, alkaline conditions also can occur and adversely affect aquatic biota.
What causes high alkaline in urine? ›The following are some of the traditional causes of alkaline urine2: (1) urinary tract infection (Proteus and others); (2) metabolic alkalosis (pyloric stenosis and others); (3) failure of acidification (renal tubular acidosis, chronic renal failure, or aldosterone abnormalities); (4) ingestion (salicylate, sodium ...
What color is acidic urine? ›The color of urine can be influenced by: - pH: acidic urine usually darker. - concentration: pale yellow urine is usually hypotonic, while dark urine is hypertonic (except in osmotic diuresis -e.g. in glucosuria- where the pale colored urine has high specific weight).
Is it normal to have oxalates in urine? ›Oxalate is a natural chemical in your body, and it's also found in certain types of food. But too much oxalate in your urine can cause serious problems. Hyperoxaluria can be caused by inherited (genetic) disorders, an intestinal disease or eating too many oxalate-rich foods.
How do you read urinalysis results? ›- Color – Yellow (light/pale to dark/deep amber)
- Clarity/turbidity – Clear or cloudy.
- pH – 4.5-8.
- Specific gravity – 1.005-1.025.
- Glucose - ≤130 mg/d.
- Ketones – None.
- Nitrites – Negative.
- Leukocyte esterase – Negative.
Hyperoxaluria is a condition that occurs when there is too much oxalate in your urine. Kidney stones are usually the first symptom. The goal of treatment is to lower the level of oxalate in the body and prevent calcium oxalate crystals from forming in the kidneys and other body tissues.
How does pH affect kidney stones? ›When the pH of urine drops below 5.5, urine becomes saturated with uric acid crystals, a condition known as hypercalciuria. When there is too much uric acid in the urine, stones can form. Uric acid stones are more common in people who consume large amounts of protein, such as that found in red meat or poultry.
What happens if urine becomes acidic? ›
This rids the body of stomach acid, which can make body fluids more basic. Acidic urine can also create an environment where kidney stones can form. If a person has low urine pH, meaning that it is more acidic, it might indicate a medical condition, such as: diabetic ketoacidosis, which is a complication of diabetes.
Does acidic urine dissolve kidney stones? ›Uric acid stones are more common than cystine stones and often form in people with diabetes. Uric acid and cystine stones form in urine that is acidic (pH 5-5.5). Diabetics usually have persistently acid urine. Both uric acid and cystine stones can be dissolved if the urine is made alkaline (pH 6-7).
Are kidney stones acidic or alkaline? ›Changes in Urine Acidity
Changes in the acid balance of the urine can affect stone formation. Uric acid and cystine stones mainly form in acidic urine. Calcium phosphate and struvite stones increase in alkaline urine.
Normal Results
The normal values range from pH 4.6 to 8.0.
Citrate, not phosphate, can dissolve calcium oxalate monohydrate crystals and detach these crystals from renal tubular cells.
What does presence of calcium oxalate in urine indicate? ›Calcium oxalate
They're colorless and can be found in healthy urine. Calcium oxalate crystals are heavily associated with kidney stones, which can form when too much oxalate (found in such foods as spinach) is in the system.
For example, urine with a lower pH (more acidic) tends to inhibit the growth of bacteria, and urine that is high in ammonia (more alkaline or basic) may impede the body's immune response to a urinary tract infection.
What does a pH of 6.5 in urine mean? ›Bacteriuria with urine pH above 6 to 6.5 suggests struvite stones. Urine should be cultured, and because many bacteria produce urease even when urine bacterial colony counts are low, the microbiology laboratory should be instructed to type the organism even if there are fewer than 100,000 colony-forming units/ml.
Does water intake affect urine pH? ›Baseline urine pH values lower than or equal to 5.8 resulted in increased values, while baseline values greater than or equal to 6.5 gave decreased values. Mean increase in pH as a result of greater water intake was 0.57 units.
Is calcium oxalate basic or acidic? ›Calcium oxalate is a combination of calcium ions and the conjugate base of oxalic acid, the oxalate anion. Its aqueous solutions are slightly basic because of the basicity of the oxalate ion.
Is calcium oxalate acidic or alkaline? ›
Calcium oxalate develops in acidic urine (pH less than 6.0). Calcium phosphate develops in alkaline urine (pH greater than 7.5).
Does apple cider vinegar dissolve calcium oxalate kidney stones? ›Apple cider vinegar contains acetic acid which helps dissolve kidney stones. In addition to flushing out the kidneys, apple cider vinegar can also decrease any pain caused by the stones. In addition, water and lemon juice can help flush the stones and prevent future kidney stones.
Does calcium make urine more alkaline? ›Patients being treated for renal calculi are frequently given diets or medications to change the pH of the urine so that kidney stones will not form. Calcium phosphate, calcium carbonate, and magnesium phosphate stones develop in alkaline urine; when this occurs, the urine is kept acidic.
What does acidic urine pH mean? ›If your urine sample has a lower-than-normal pH, this could indicate an environment conducive to kidney stones. Other conditions that prefer an acidic environment are: acidosis. diabetic ketoacidosis, which occurs when ketones build up in the body. diarrhea.
What causes high alkaline in urine? ›The following are some of the traditional causes of alkaline urine2: (1) urinary tract infection (Proteus and others); (2) metabolic alkalosis (pyloric stenosis and others); (3) failure of acidification (renal tubular acidosis, chronic renal failure, or aldosterone abnormalities); (4) ingestion (salicylate, sodium ...