Renal calculi
Renal calculi, commonly known as kidney stones, are hard crystals formed from deposits of minerals and salts that can build up inside the kidneys. Renal calculi are common in people with SCI and various types of calculi can occur, usually influenced by diet.
Oxalate calculi
- Calcium oxalate calculi is the most common form of calculi (~80%) and usually passed spontaneously.
- Oxalate is detected in:
- Seeds (cereals/grains)
- Leaves (spinach)
- Roots (beets)
- Low levels of oxalate are found in peas, corn, broccoli, oranges and cornflour.
- Half of the urinary oxalate is sourced from the diet.
- An increase in oxalate absorption, in people who form calculi, can be caused by an absence of oxalate-degrading bacteria in the digestive tract.
- Other factors that can cause the formation of calculi are:
- Urinary stasis
- Intermittent high levels of oxalate
- Immobilisation
- Metabolic disorders
- A diet high in sodium, processed sugar and protein.
Recommendations:
- An annual kidney ultrasound and x-ray are recommended.
- Increase vegetable and water intake.
- See Dietary Guidelines for Preventing Kidney Calculi.
Ammonium magnesium phosphate calculi
- Ammonium magnesium phosphate calculi are better known as infection calculi and have a higher risk of recurrence.
- These calculi, containing ammonium magnesium phosphate and calcium phosphate, are secondary to an infection with a urease-producing bacteria.
- Staphylococcus aureus and Proteus are the most common causes of calculi.
Recommendations:
Uric acid calculi
- Uric acid calculi are formed from purine ingestion (beer and animal protein) and a diet high in carbohydrates and phosphorus.
- The calculi also develop in conjunction with other factors, such as urinary stasis, obesity and low urine pH.
- The low urine pH is caused by a high dietary intake of animal proteins.
Recommendations:
- An annual kidney ultrasound and x-ray are recommended.
- Increase intake of vegetables and water.
Renal calculi checklist
Is the person:
- Drinking 2-3 litres of water a day, at regular intervals?
- Maintaining a free-flowing drainage system?
- Eating a well-balanced diet?
- Maintaining a clean and closed system?
- Changing the catheter at least every 4-6 weeks or when commencing antibiotic therapy?
- Mobilising, as able?
- Taking appropriate medications?
Clinical investigations:
- Test urine pH.
- Take a micro-urine.
- Have regular annual kidney ultrasounds and x-rays and have the test results checked by a specialist.
Dietary guidelines for preventing renal calculi
The most common type of renal calculi results from too much calcium and oxalate in the urine. These minerals bind together as crystals, forming calculi. The following dietary guidelines can help to prevent kidney calculi.
Drink more fluid, especially water.
- Drinking water helps to flush out the kidneys and dilute calculi-forming substances, making calculi less likely to form.
- Encourage at least 2-3 litres, or 10 cups, of fluid daily. At least half of this should be water (soda, mineral, spring or plain tap water).
- Have a cup of fluid (250ml) each hour during waking hours, and a large glass of water before going to bed. Encourage a glass of water if the person wakes up during the night.
- Spread out the fluid intake during the day.
- AVOID strong black tea and orange juice, as these are high in oxalates.
- Colas are also high in phosphates, which can contribute to calculi.
Salt (sodium) increases the amount of calcium in the urine. To reduce salt:
- Buy fresh foods, or foods without salt – fruit, fresh vegetables, fresh meats, chicken, fish, eggs, porridge, rice and pasta.
- Most sodium (75%) comes from processed foods. Limit processed foods high in salt, e.g. soup, Bonox, processed meats, sauces, gravy, crisps and snack foods.
- ‘Low salt’ or ‘no added salt’ foods are the best choices. Look for a sodium content of less than 150mg per serve as a guideline. Note that some ‘reduced salt’ products can still contain high levels of sodium.
- Do not add salt at the table or in cooking. Instead, add extra flavour to meals with the following:
- Freshly ground pepper or dry mustard powder
- Lemon juice, lime juice or vinegar
- A sprinkle of dried herbs or chopped fresh herbs
- Garlic, curry, chilli, onion, fresh ginger or spring onions
Reducing oxalate in the diet helps to reduce the amount of oxalate in your urine. Foods to avoid are:
- Rhubarb, spinach, silver beet, beetroot, eggplant, sweet potato, celery and leeks
- Nuts and peanut paste
- Strong black tea and orange juice
- Chocolate
- Wheat bran and wheat germ
- Berries (e.g. strawberries, blackberries) and dried figs
- Soy sauce and Worcestershire sauce
- Dietary calcium is important for bones and teeth. A high calcium intake reduces the chance of kidney calculi forming.
- Do not limit dairy foods. Too little calcium can cause oxalate levels to rise
- Calcium in the digestive tract binds to oxalate from food and keeps it from entering the blood, and then the urinary tract, where it can form calculi. Include at least 2-3 choices from the following list:
- 250mL milk, e.g. Trim, skim, full cream, calcium-fortified soy milk
- 200mL high calcium milk, e.g. Physical
- 200g (small tub) yoghurt
- 40g cheese (2 slices)
- 3 scoops ice-cream
- Limit protein from meat, seafood, fish, chicken and eggs to a moderate serve (120-150g) daily (cooked). Note: 60g meat = 2 eggs.
- High protein reduces citrate, a chemical in urine that prevents calculi from forming.
Speak with your doctor before taking:
- Vitamin C supplements(also known as ascorbic acid and calcium ascorbate) unless directed by your doctor
- Vitamin D supplements or cod liver oil.
QSCIS acknowledges the Urology Department, Princess Alexandra Hospital for assistance in updating and writing this information
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Shepherd AJ, Mackay WG, Hagen S: Washout Policies in Long Term Indwelling Urinary Catheterisation in Adults. Cochrane Database of Systematic
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