What Are Uric Acid Stones

  • Afsheen Hidayat MSc in Clinical Microbiology, Queen Mary University of London, UK

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Uric acid stones are a type of kidney stones. Kidney stones are a common urological problem that can cause extreme pain and discomfort. Uric acid stones can be treated with pain relief and surgical intervention, if needed, to remove the stone.

Introduction

Uric acid stones are a type of stone that can be formed in the kidney and are one of the four types of kidney stones. Kidney stones are solid formations composed of minerals and salts, which may develop within the kidneys and impact any section of the urinary tract. Stones can be formed when urine becomes concentrated. Uric acid stones are a type of kidney stone that forms when there is an excessive amount of uric acid in the urine. Uric acid is a byproduct generated during the breakdown of purines, substances present in specific foods and also naturally produced by the body. Uric acid normally dissolves in urine and is eliminated from the body. However, uric acid crystals can form when there is an excessive generation of uric acid or if the urine becomes overly concentrated. 

Various factors, including dietary choices, obesity, certain medical conditions, specific supplements, and medications, can contribute to the formation of kidney stones. When the pH of the urine is constantly low, uric acid urinary stones are frequently observed. Uric acid crystals do not dissolve in an acidic urine and result in the formation stones.1

The global incidence of uric acid stones is on the rise, affecting individuals of all genders, ages, and racial backgrounds. They are most commonly found in males aged 60-65. The prevalence in Europe is between 5 and 10%, and recurrence rates have also increased. In the United Kingdom, there has been a 63% increase in kidney stone episodes [I think more information/reference is required to support this statement]. 

As the occurrence of stone disease increases and surgical treatments become more common, there is a substantial financial burden on both patients and the economy.2 Uric acid stones make up 10 to 15% of all urinary tract stones. 

Causes of uric acid stones

  • Diet - Diet significantly influences the development of uric acid stones, as foods rich in purines can lead to increased levels of uric acid. Some examples of purine-rich foods include red meat, organ meats (like liver and kidneys), certain seafood (such as anchovies and sardines), and alcoholic beverages, particularly beer.
  • Medical Conditions such as:
    • Gout is a condition marked by elevated levels of uric acid in the bloodstream, heightening the likelihood of developing uric acid stones. The excess uric acid can form crystals in the joints, causing pain and inflammation.
    • Hyperuricemia: This is a condition where there is an abnormally high level of uric acid in the blood. Hyperuricemia can be caused by genetic factors, certain medical conditions, or medications.
  • Dehydration - Not consuming enough fluids can result in urine becoming more concentrated, thus facilitating the formation of uric acid crystals.
  • Low urine pH - a decreased urinary pH is the primary risk factor for uric acid stone formation in the urine. Uric acid crystals do not dissolve in acidic urine and result in the formation of stones.4

Risk factors

The various factors that can increase the risk of developing kidney stones include:

  • Family or personal history of having kidney stones.
  • Dehydration - inadequate daily water intake can heighten the risk of kidney stone formation. 
  • Certain diets - Consuming foods rich in salts and sugar can elevate the likelihood of developing uric acid stones. 
  • Obesity - Elevated body mass index (BMI), larger waist circumference, and weight gain have been associated with a heightened risk of uric acid stone formation. 
  • Medical conditions - the likelihood of developing uric acid stones rises in medical conditions like type 2 diabetes and metabolic syndrome.
  • Gastric bypass surgery, performed for weight loss purposes, can lead to alterations in the digestive process that impact the absorption of calcium and water, consequently heightening the risk of stone formation.
  • Other important risk factors for uric acid stones include:
    • Age 
    • Hot and dry environmental conditions can cause sweating and lead to dehydration.
    • Sex
    • Decreased urine volume 

Signs and symptoms 

Uric acid stones have similar symptoms to other types of kidney stones. The symptoms result from irritation or blockages inside the kidneys or urinary tract. The main symptoms associated with uric acid stones include:

  • Lower back or flank pain - severe pain in the lower back or side, often referred to as "renal colic." The pain can come in waves and may radiate to the lower abdomen and groin.
  • Blood in the urine - Blood in the urine is called haematuria. It may cause the colour of the urine to turn pink, red, or brown.
  • Nausea or vomiting.
  • Fever and chills.
  • Foul-smelling or cloudy urine.
  • Frequent Urination - people with uric acid stones may feel the need to urinate more frequently, even if there is little urine produced.

Diagnosis

The possible diagnostic tests that can be used include:

  • Blood tests - Blood tests can be used to detect too much uric acid or calcium in blood. These tests can measure uric acid levels in the blood and detect signs of kidney dysfunction or infection.
  • Urine test - A 24-hour urine test can be used to test for the presence of too much calcium and uric acid in urine.
  • Imaging Tests - CT scans and ultrasounds can help visualize the stones and their location in the urinary tract. Abdominal X-rays are not usually used because they may miss smaller stones.

Management and treatment 

  • Management of uric acid stones mainly consists of pain relief and possible surgical intervention to remove stones. Pain Relief includes medications such as nonsteroidal anti-inflammatory drugs (NSAIDs) or opioids that may be prescribed to manage pain during a stone episode.
  • Medications to dissolve stones - in some cases, medications like allopurinol or sodium bicarbonate may be used to dissolve uric acid stones.
  • Extracorporeal Shock Wave Lithotripsy (ESWL) - ESWL is a non-invasive procedure that uses shock waves to break down kidney stones into smaller fragments, making them easier to pass.
  • Ureteroscopy - in cases where stones are too large or cannot be broken down with ESWL, a ureteroscopy may be performed to remove or fragment the stones.

Lifestyle modifications

  • Exercise - engaging in regular physical activity can assist in preserving a healthy weight and decreasing the likelihood of developing kidney stones.
  • Weight Management - obesity is a risk factor for kidney stones, so maintaining a healthy weight through diet and exercise is important.
  • Dietary Changes - to reduce the risk of uric acid stone recurrence, individuals may be advised to limit purine-rich foods and increase the consumption of water and low-purine foods like fruits, vegetables, and whole grains.
  • Increased fluid intake - staying well-hydrated helps dilute urine and prevent the formation of uric acid crystals.

Complications

Uric acid stones can lead to various complications if not properly managed or treated. The common complications associated with uric acid stones are:

  • Recurrence - one of the primary complications is the recurrence of uric acid stones. If the underlying causes, such as dietary habits or medical conditions like gout, are not addressed, individuals may experience repeated episodes of stone formation.
  • Obstruction - uric acid stones, like other kidney stones, can obstruct the urinary tract. When a stone becomes lodged in the ureter (the tube connecting the kidney to the bladder), it can block the flow of urine, causing severe pain and discomfort.
  • Urinary Tract Infections (UTIs) - obstructed urine flow due to a uric acid stone can lead to stagnant urine in the urinary tract, creating an environment conducive to bacterial growth and increasing the risk of urinary tract infections.
  • Hydronephrosis - prolonged obstruction of the urinary tract can cause a build-up of urine in the affected kidney, a condition known as hydronephrosis. This can lead to stretching and pressure on the kidney, potentially causing kidney damage if not relieved promptly.
  • Kidney Damage - chronic or recurrent uric acid stone formation can lead to kidney damage over time. The kidney's filtering function may be impaired, and this can contribute to the development of chronic kidney disease (CKD).
  • Sepsis - in severe cases, when a urinary tract infection caused by a stone is not promptly treated, it can lead to sepsis — a life-threatening infection that can spread throughout the body.
  • Complications during stone removal - if surgical intervention is necessary to remove a uric acid stone, there can be potential complications associated with the procedures, such as infection, bleeding, or injury to nearby organs.
  • Chronic pain - even when not actively causing acute symptoms, uric acid stones can lead to chronic discomfort or intermittent pain in the lower back or abdomen.
  • Impaired kidney function - prolonged obstruction, recurrent infections, or kidney damage caused by uric acid stones can result in impaired kidney function, which may require ongoing medical management and monitoring.

Conclusion

In conclusion, uric acid stones are a type of kidney stone that can be a significant urological concern and can lead to excruciating pain and potential complications if left untreated. Understanding their causes, symptoms, and treatment options is essential for managing and preventing their recurrence. various factors such as diet, medical conditions like gout and hyperuricemia, and dehydration can contribute to the formation of uric acid stones. Recognizing the symptoms early and seeking prompt medical attention is crucial. The possible treatment options mainly consist of pain relief and surgical interventions. Moreover, lifestyle modifications such as dietary changes, increased fluid intake, exercise, and weight management play a vital role in preventing their recurrence.

References

  1. Cicerello E. Uric acid nephrolithiasis: An update. Urologia [Internet]. 2018 Aug [cited 2023 Sep 29];85(3):93–8. Available from: http://journals.sagepub.com/doi/10.1177/0391560318766823
  2. Wong YV, Cook P, Somani BK. The association of metabolic syndrome and urolithiasis. Int J Endocrinol [Internet]. 2015 [cited 2023 Sep 29];2015:570674. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4385647/
  3. Kc M, Leslie SW. Uric acid nephrolithiasis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Sep 29]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK560726/
  4. Mehta TH, Goldfarb DS. Uric acid stones and hyperuricosuria. Advances in Chronic Kidney Disease [Internet]. 2012 Nov 1 [cited 2023 Sep 28];19(6):413–8. Available from: https://www.sciencedirect.com/science/article/pii/S1548559512001516

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Afsheen Hidayat

M.B.B.S, MSc in Clinical Microbiology

Afsheen possesses a strong background in both the medical and scientific disciplines and is a highly educated health researcher. She is a medical expert who is eager to pursue a career in clinical research and medical writing because she believes that it is crucial to improve patient outcomes and provide better medical care. After working as a clinician in Dubai, she came to realise that her goal was to use her extensive research skills to raise the standard of healthcare. She obtained an MSc in Clinical Microbiology from Queen Mary University of London to advance her research career, and she is currently working as a medical writer.

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