Kidney Stone Types: Complete Guide to Causes, Symptoms, and Prevention

Key Takeaways

• Kidney stones come in five main compositions, each with distinct causes.
• Calcium‑based stones are the most common, but diet, infection and genetics matter.
• Laboratory analysis of the stone is the definitive way to identify its type.
• Tailored prevention - more water, specific dietary tweaks, or medication - cuts recurrence dramatically.
• Seek urgent care for severe pain, fever, or blood in the urine.

When a mineral crystal builds up in the urinary tract, a kidney stone is formed. Kidney stones affect roughly 1 in 10 people worldwide, and their pain can feel like the worst cramp you’ve ever endured. The good news? Knowing the stone’s composition lets you pick the right diet, fluids, and medication to keep new stones from forming.

How Kidney Stones Form

Every day your kidneys filter about 150liters of blood, extracting waste and excess minerals. Normally, these substances dissolve in urine and exit the body harmlessly. When urine becomes too concentrated, or when certain chemicals bind together, they can crystallise. Over time the crystals grow into stones that may lodge in the kidney, ureter, or bladder.

Major Types of Kidney Stones

Scientists classify stones by what they’re made of. Five types account for the overwhelming majority of cases:

Calcium Oxalate Stones

Calcium oxalate stone is the most prevalent, responsible for about 70‑80% of all stones. They form when calcium binds with oxalate, a natural waste product found in foods like spinach, nuts, and chocolate. High oxalate intake, low urine volume, and hypercalciuria (excess calcium in urine) all raise the risk.

Calcium Phosphate Stones

Calcium phosphate stone makes up roughly 10‑15% of cases. These stones usually appear in people with alkaline urine, certain metabolic disorders, or chronic urinary infections. Diets rich in dairy and certain supplements can increase phosphate levels.

Uric Acid Stones

Uric acid stone is the third most common type, especially in men and people with gout. High purine intake (red meat, organ meats, seafood) raises uric acid in the blood, which can precipitate when urine is acidic. Rapid weight loss and dehydration also contribute.

Struvite Stones (Magnesium Ammonium Phosphate)

Struvite stone, also called magnesium ammonium phosphate stone, forms rapidly after urinary tract infections with urease‑producing bacteria (e.g., Proteus). They can grow large, cause blockage, and sometimes form staghorn calculi that fill the kidney’s collecting system.

Cystine Stones

Cystine stone is rare, accounting for less than 1% of stones, and results from a hereditary defect called cystinuria. The kidneys leak cystine, a poorly soluble amino‑acid, into the urine, which then crystallises.

How to Identify the Stone Type

The only way to know a stone’s exact makeup is through analysis after it’s passed or removed. Here’s the typical workflow:

1. Imaging: A non‑contrast CT scan shows stone size, location, and density (measured in Hounsfield units). Higher density often points to calcium‑based stones.
2. Urine testing: 24‑hour urine collections reveal supersaturation of calcium, oxalate, uric acid, citrate, and other markers.
3. Stone analysis: Infrared spectroscopy or X‑ray diffraction determines the precise mineral composition.

Armed with this data, your clinician can tailor preventive therapy.

Prevention Strategies Tailored to Each Stone Type

While all stone formers benefit from basic habits, fine‑tuning your approach to the stone’s chemistry yields the biggest payoff.

Calcium Oxalate

• Drink at least 2‑3L of water daily to keep urine volume>2L.
• Limit high‑oxalate foods (spinach, rhubarb, almonds) if you’re a frequent oxalate former.
• Consume dietary calcium (1g/day) with meals to bind oxalate in the gut, reducing absorption.
• Consider potassium citrate supplementation if urine citrate is low.

Calcium Phosphate

• Maintain urine pH between 5.5-6.5; avoid excessive alkali (bicarbonate) unless prescribed.
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• Reduce sodium intake (<2g per day) because high sodium drives calcium excretion.
• Limit animal protein that can increase urinary phosphate.

Uric Acid

• Alkalinise urine with potassium citrate to keep pH>6.0, which solubilises uric acid.
• Cut purine‑rich foods (red meat, shellfish) and fructose‑sweetened beverages.
• Maintain a healthy weight; rapid dieting spikes uric acid.

Struvite

• Promptly treat urinary tract infections; a short course of culture‑directed antibiotics can prevent stone regrowth.
• Ensure regular bladder emptying; consider a low‑sodium diet to reduce urinary phosphate.
• In recurrent cases, a low‑dose urease inhibitor (e.g., acetohydroxamic acid) may be prescribed.

Cystine

• Increase fluid intake dramatically - aim for >4L/day to keep cystine concentration low.
• Alkalinise urine to pH7.5-8.0 with potassium citrate or bicarbonate.
• Thiols such as tiopronin can bind cystine, making it more soluble (used under specialist supervision).

When to Seek Medical Care

If you experience any of the following, call emergency services or your urologist immediately:

• Severe, colicky flank pain that radiates to the groin.
• Fever>38°C (100.4°F) or chills, indicating possible infection.
• Visible blood in the urine (gross haematuria).
• Persistent nausea, vomiting, or inability to pass urine.

Early intervention can relieve pain, prevent kidney damage, and avoid complications like sepsis.

Comparison of Kidney Stone Types

Frequently Asked Questions