What Are Struvite Stones?

Struvite stones are the result of a urinary tract infection, They are hard objects composed of chemicals such as calcium, magnesium, ammonium and phosphate. These stones can form in the kidneys or bladder of people with urinary infections, retention and or with caterers and are known to have a rapid growth compared to calcium stones and can fill up the kidney if left untreated.

Stones might remain in the kidney or travel through the urinary tract, they can cause pain, obstruction, infection and significant health problems.

Struvite stones have a 5 to 15% percentage of formation among other types of kidney stones and account for 30% of all cases of kidney stones worldwide.^1,2

What causes struvite stones?

One of the major conditions favouring the formation of struvite kidney stones are urinary tract infections, also named infection stones. The presence of an upper urinary tract infection from bacteria can lead to less acidic urine, this is caused by infection-causing bacteria that produce ammonia which can make the urine less acidic leading to the formation of stones.

Infection with Proteus, Klebsiella, Staphylococcus, Pseudomonas, Providencia, Serratia, and Morganella can lead to the formation of stones, because of their ability to release urease which favours the formation of struvite kidney stones. The presence of these kidney stones is more common in people assigned female at birth as they are more likely to contract a urinary tract infection than people assigned male at birth. People assigned female at birth are three times more likely to contract struvite stones than people assigned male at birth.¹

Other conditions which can lead to an increased risk of struvite kidney stones are:²

• Advanced age
• Hypertension
• Neurogenic bladder
• Internal caterers
• Medullary sponge kidney
• Distal tubular acidosis
• Diabetes
• Malformations and abnormalities which lead to urinary retention

Formation of struvite stones

Role of magnesium, ammonium and phosphate

Magnesium and phosphate are naturally present in urines, the first plays a role in crystallisation. Phosphate combines with magnesium and ammonium to form struvite crystals in the presence of an alkaline pH. Ammonia is produced in urine by bacteria, an increase in ammonia and ammonium leads to high pH, an alkaline environment where struvite forms more easily.

In short

• Ammonium increases pH, causing an alkaline environment
• Magnesium binds with phosphate and forms crystals called magnesium ammonium phosphate a component of struvite stones
• Phosphate, in alkaline environments, combines with the other two forming struvite crystals

The combination of these 3 components leads to the gradual combination of struvite crystals leading to its growth, which forms struvite stones.¹ 

What symptoms do struvite stones cause?

Struvite stones can be asymptomatic especially when too small and can pass through with no problems. However, these stones can become too enlarged leading to significant pain, backup of urine and other significant health concerns. Noticeable symptoms include:¹

• Pain during urination
• Fever and chills
• Severe pain at the sides of the lower back
• Frequent urination
• Blood in urine
• Smelly or cloudy urines

Symptoms can also be tied to UTI, the symptoms include:

• Burning sensation during urination
• Frequent urination in small quantities
• Frequent urge to urinate

Relevant risk factors include:³

• Low hydration
• Sex – Generally people assigned male at birth have a higher risk of developing kidney stones however people assigned female at birth have a higher risk of developing struvite kidney stones
• Infections and diseases – Struvite stones can be caused by persistent and uncured UTIs
• Medical conditions – Diseases that cause inflammation such as irritable bowel syndrome, celiac disease, hormonal imbalance (hyperthyroidism), metabolic conditions (diabetes), high calcium in urines, and surgeries such as gastric bypass can increase the risk of struvite kidney stones
• Age – Generally kidney stones can develop between the age group of 20-50, struvite stones typically develop above 50
• Diet – A Diet rich in salt, proteins, oxalates and phosphates can increase the risk of kidney stones
• Lifestyle – People with sedentary lifestyles and suffering from obesity, have a higher risk of developing struvite stones
• Medication - Calcium and magnesium-based antacid salts, potassium and sodium-based diuretics (used for blood pressure) and phenytoin (used for epileptic seizures)

Potential complications of struvite stones

Struvite stones are known for their rapid growth with little to no symptoms, leading to big painful stones in no time, which can cause obstruction, damage, sepsis and discomfort.¹

In the past struvite stones were thought to be harmless when asymptomatic however, studies have shown that 30% of patients treated without surgery died of renal failure or sepsis, in a 15-year overall survival study, struvite stones have shown a survival rate of only 41%.²

How are struvite stones diagnosed?

Struvite stones can be diagnosed through physical examination, medical history, and imaging tests these involve:³

• Blood tests
• Urines exam
• Ultrasonography of the abdomen
• CT scan
• MRIs and X-rays of the abdomen
• Retrograde and intravenous pyelograms 

Blood and urine can be tested for abnormal chemical levels of calcium, phosphate, magnesium, and uric acid, urines might be collected for 24 hours to test uric acid.¹ Imaging is used to locate stones. Ultrasound is usually the most appropriate imaging scan for this condition but MRIs and CT scans can also be used.

Struvite stones passing is rare, but if a stone comes out of the body it can be analysed to understand the type of stone and causes of its formation.¹

How can we prevent struvite stones?

Because of its primary cause, which is infection, many treatments might prove ineffective. To prevent struvite stones, however, doctors might prescribe Acetohydroxamic acid (AHA) to prevent bacteria from producing ammonia, which causes stones to grow. After stone removal, you might also be prescribed antibiotics to prevent future UTIs and reduce the incidence of struvite stones. To prevent stones:

• Drink plenty of water, drink at least 12 cups of water to maintain optimal urinary and renal health (urine should appear light yellow when hydrated)
• Do not ignore your UTIs, as we said previously urinary tract infections and the bacteria causing them are the major causes of these stones, curing your urinary infections can help prevent struvite stones
• Limit foods which contain chemicals that can increase struvite stones and maintain a well-balanced diet (avoid food high in calcium, phosphorous, magnesium and oxalates)
• If at risk of struvite stones regular checkups to monitor the formation of these stones are advised

Do you suspect you are at risk of getting struvite stones? or do you show any of the symptoms previously elevated? remember to consult a healthcare professional before making any important decision regarding your health.^3,1

How are struvite stones treated?

Treatment for struvite stones doesn’t differ too much from any other renal stone treatment and includes:

• Antibiotic treatment – It has shown the ability to reduce UTI infection and limit the growth of stones
• Acetohydroxamic acid (AHA) – It is a urease inhibitor which decreases recurrence and prevents stone growth, this drug should be used with antibiotics to reach the most desired result. AHA can also reduce alkalinity in urines and lower ammonia levels. However, at least 20% of the patients treated with this drug have shown important side effects leading to a stop in treatment.
• Complete surgical removal–Recurring rates for struvite stones can reach as high as 85%, especially when residues are left behind, and the effect of the antibiotics is lower when infected struvite stones remain²
• Ureteroscopy– A tube is inserted in the urethra to remove any stones stuck in that zone

Other therapy options are:^1,2

• Extracorporeal shockwave lithotripsy, which uses an acoustic pulse to remove stones
• Percutaneous nephrolithotomy, a minor surgery involving the removal of the stone through the back
• Dissolving struvite stones–It is a very delicate therapy that uses acidifying solutions to dissolve the stone. However, this procedure is not used due to the associated side-effects such as raised blood magnesium levels²

Role of surgical intervention

Surgical intervention is usually needed when stones are too big, causing obstruction and no other treatment is effective It includes: 

• Percutaneous nephrolithotomy (PCNL)
• Ureteroscopy
• Open surgery (can be nephrolithotomy or ureterolithotomy)

After surgery, postoperative care is essential, through monitoring and pain management, imaging and periodic urine examinations are also recommended (6 to 12 months). In the case of patients who show rapid recurrence of struvite stones examination might be more frequent.

PNCL is considered the most appropriate treatment for struvite stones.^1,2

Prevention of struvite stone formation

This condition can develop very rapidly and maintaining a well-balanced diet, low in phosphorus, magnesium and oxalates, and good hydration can be the key to prevention.

Stay vigilant of your symptoms, remember to seek medical attention, and consult a medical professional before starting any treatment plan to ensure the best approach is adopted for your needs.

Summary

• Struvite stones are hard objects composed of chemicals such as calcium magnesium, ammonium, and phosphate that form in the kidneys or bladder due to urinary tract infections
• These stones have a rapid growth rate compared to calcium stones and can fill up the kidney if left untreated
• Conditions that favour the formation of struvite stones include urinary tract infections, advanced age, hypertension, neurogenic bladder, internal catheters, and more
• The presence of specific bacteria and an alkaline urine pH are also factors that contribute to the formation of struvite stones