Preventing Kidney Stones

The treatment of urinary stone disease extends beyond the acute management of stones as this condition yields a high rate of recurrence.

Approaches for stone prevention includes both dietary interventions and medication. The use of medication should be guided by the 24-hour urine analysis.


What can a patient do about being diagnosed with stones?

In one case, a patient, Mark (not his real name), was sleeping when he felt a severe pain in his left back. Upon seeking help, he discovered a stone in his kidney and underwent shockwave lithotripsy, which cleared the stone.

Urinary stone disease is a relatively common condition thought to affect 15% of the population and with a slowly increasing trend. This could be associated with heightened rates of diabetes and obesity. After treatment, there is a 25 to 50% chance of recurrence within five years. Thus, in many cases, urinary stone disease is a chronic condition. This is more so when the patient possesses risk factors for recurrence.

what can be done to prevent a recurrence?

1. Evaluation

First, patients with urinary stone disease should be evaluated. The baseline evaluation for this condition requires a proper medical and dietary history. Physical examinations should include blood tests to look for abnormalities in uric acid, calcium and kidney functions, and a urine dipstick test to detect infections and measure urinary pH levels. For patients with a higher risk of recurrence (Table 1), a 24-hour urine test to look for abnormalities should be obtained. In a pilot study conducted by Tan Tock Seng Hospital, it was found that 95% of patients with high risk of stone formation were found to possess abnormalities after undergoing the 24-hour urine analysis. The correction of these abnormal urine parameters can significantly reduce the recurrence of stones. An added benefit of doing metabolic evaluations is that underlying systemic diseases that manifest as stone diseases can be detected. They may include conditions such as hyperparathyroidism, renal tubular acidosis and hyperoxaluria.

 

2. Management Strategies

The main aims of treatment are to improve the solubility of kidney stones, introduce inhibitors to stone formation and also normalise abnormal urinary levels of calcium and oxalate. Improved solubility of the stones can be achieved by dilution and maintaining a neutral or slightly higher pH, while the main inhibitor of stone formation is citrate. Normalising urinary calcium and oxalate levels can be done through dietary and medical means.

(a) Dietary Management
There are a number of dietary interventions that can be applied to reduce stone recurrence.

Basic Dietary Management 

Fluids 

First and foremost, patients with stone disease should be encouraged to drink more fluids to produce at least two litres of urine a day, unless contraindicated. A simple gauge of adequate fluid intake is in the colour of the urine. If it is dark, fluid intake is inadequate. Patients with stones should aim for very light to clear coloured urine.

A study by Borghi et al1 found that increasing fluid intake would reduce the risk of recurrent stone disease by 50%. Lemonade and orange juice are recommended as the citrate in these juices helps to reduce stone recurrence. The citrate alkalises urine and can also combine with calcium to form a soluble salt, thus stopping stone precipitation. Soft drinks should be avoided as they have been shown to be associated with increased stone episodes2.

Salt 

Patients should also be on a salt restriction diet. They should aim to consume not more than 3g per day, which is equivalent to half a teaspoon of salt. This would help reduce urinary calcium excretion, which could precipitate as stones in the urinary system.

Animal Protein 

Animal proteins can lead to increased uric acid (via purine metabolism) in the blood and acidification of the urine, which will increase the incidence of calcium oxalate and uric acid stones. Consumption of animal proteins should be limited to not more than 0.8 to 1g per kg of the body weight per day (e.g. egg: 7g, fillet of salmon: 22g, 100g of chicken: 26g). In a recent study, it was found that fish and chicken actually caused as much uric acid issues as beef3.

 

Vegetables 

Fibre and vegetables should be encouraged as this raises pH levels and reduces incidence of stones by improving the solubility of stones. Citrate is also found in many fruits and vegetables.

Supplements 

Vitamin C consumption should be limited to 500mg per day, unless otherwise specified. Dosing more than 1g or more has been shown to be associated with increased calcium oxalate stone formation as the excess ascorbic acid is converted to oxalate4.

A normal calcium intake of 800mg per day should be adhered to5. This is because when calcium is taken together with high oxalate foods, it binds oxalate in the gut and prevents oxalate absorption. Hence, a low calcium diet would lead to excessive absorption of oxalate and subsequently increase the incidence of calcium oxalate stones.

It is advisable for patients to take a 300mg tablet of calcium along with high oxalate meals, to try and ameliorate the effects of oxalate. Calcium supplementation in the form of calcium citrate is a better alternative as one would enjoy the benefits of calcium and citrate intakes.

Diets 

Specific dietary plans can have effects on stone disease. The Atkins diet and ketogenic diets are more likely to cause stones, whereas the Dietary Approaches to Stop Hypertension (DASH) and vegetarian diets tend to reduce stone formation. This is expected as the Atkins diet, with a high animal protein load, tends to lead to acidic urine, which promotes the precipitation of kidney stones. Increased purine loads from the diet may also make the patient prone to uric acid stones.

 

Directed Dietary Management When a proper dietary history and 24-hour urine test are done, we can tailor the dietary management to correct the abnormalities found in the urine test. 

Oxalate restriction 

Oxalate restriction in the diet is controversial. This is because oxalate is found in a lot of vegetables that have beneficial effects in the prevention of stone formation and also cardiovascular health. Oxalate restriction should be done in moderation and options like consuming calcium at the time of a high oxalate meal may be a better option. In the event that oxalate restriction is used, it is usually suggested to remove the most prominent source of oxalate, commonly found in spinach.

 

(b) Medications
In situations where there are significant abnormalities in the 24-hour urinalysis that cannot be corrected by diet alone, medications can be started to help correct the abnormalities. These can range from the use of potassium citrate, thiazide diuretics and allopurinol, depending on the abnormalities found.

Potassium citrate has the ability to alkalise the urine and also reduce the formation of calcium oxalate and calcium phosphate stones. It is used when increasing citrate with dietary interventions are insufficient. Thiazides also help to reduce calcium-based stones by increasing renal tubular reabsorption of calcium and thus lowering urinary calcium levels.

Mark was also noted to have bilateral small stones and his 24-hour urinalysis was found to have a citrate deficit. As it was mild, apart from basic dietary advice, he was advised to increase his intake of citrate in the form of orange juice and lemonade. A repeat 24-hour urinalysis showed that this corrected his citrate deficit. Today, Mark has not had a recurrence of stone disease in the past five years.

Urinary stone disease is a chronic condition. Recurrent stone disease can be prevented if a suitable approach is taken to prevent recurrence.

 

Dr Tan Yung Khan 

Dr Tan Yung Khan is a Consultant in the Department of Urology at Tan Tock Seng Hospital. He is also the Director of Endourology and Co-director of the Minimally Invasive Urology Fellowship and a clinical lecturer at National University of Singapore (NUS) School of Medicine. Dr Tan completed his Urology training in Singapore and received the National Medical Research Council (NMRC) scholarship to do advanced research in robotic surgery and minimally invasive surgery at University of Texas Southwestern Medical Center, Dallas, Texas. He also matched in the Endourology Society training programme in the United States and spent a year at Columbia Medical Center, New York City focusing on endourology and the management of stone disease.

References 

  1. Borghi L, Meschi T, Amato F, Briganti A, Novarini A, Giannini A. Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomised prospective study. The Journal of urology. 1996;155(3):839-43.
  2. Shuster J, Jenkins A, Logan C, Barnett T, Riehle R, Zackson D, et al. Soft drink consumption and urinary stone recurrence: a randomised prevention trial. Journal of clinical epidemiology. 1992;45(8):911-6.
  3. Tracy CR, Best S, Bagrodia A, Poindexter JR, Adams-Huet B, Sakhaee K, et al. Animal protein and the risk of kidney stones: A comparative metabolic study of animal protein sources. The journal of urology. 2014.
  4. Thomas LD, Elinder CG, Tiselius HG, Wolk A, Akesson A. Ascorbic acid supplements and kidney stone incidence among men: a prospective study. JAMA internal medicine. 2013;173(5):386-8.
  5. Candelas G, Martinez-Lopez JA, Rosario MP, Carmona L, Loza E. Calcium supplementation and kidney stone risk in osteoporosis: a systematic literature review. Clinical and experimental rheumatology. 2012;30(6):954-61.