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Introduction   

Kidney stone disease, also referred to as renal calculi, nephrolithiasis, or urolithiasis, is a common condition that is becoming increasingly prevalent in the United States (US) and worldwide. In the US, an estimated one in 11 people are likely to have kidney stones in their lifetime. Traditionally, men are more likely to develop kidney stones, although studies show that there is an increase in the number of incidences in women. The mortality rate from kidney stones is infrequent, although it is known to decrease one’s kidney function by 28% [6, 8]. 

Definition 

Renal calculi are deposits formed by waste products in the blood from crystals within the urinary system, which includes the kidneys and bladder [1]—several predisposing factors, such as metabolic, genetic, endocrinopathy, or environmental, cause kidney stones. The formation of kidney stones is attributed mainly to environmental factors such as warmer temperatures, which can lead to people developing dehydration, which explains why it is more prevalent in warmer regions [6]. Dehydration causes a decrease in urine volume or increased excretion of waste products such as calcium, oxalate, uric acid, phosphate, and xanthine [10].  

Kidney stones are also known to be associated with a high risk of developing cardiovascular and metabolic disease [6]. Kidney stones vary in size and can pass through the urinary tract without causing symptoms or significant complications. Often, kidney stones are asymptomatic until they migrate from the kidneys through the ureters and into the bladder, causing severe or colicky pain [1]. 

Epidemiology 

Nephrolithiasis is a common condition that has become increasingly prevalent in the United States (US). Occurrences of nephrolithiasis are typically seen in the summertime. Kidney stones affect nearly 1 in 11 people in the United States at some point in their lifetime. There is a higher incidence of kidney stones in men (10.6%), than women (7.1%) [8]. Kidney stones are more prevalent in white men, followed by Hispanics and Asians.  

According to the National Health and Nutritional Examination Survey [2], the prevalence of self-reported kidney stones increased from 3.2% in the late 1980s to 8.8% in 2014. There is a 50% chance of relapse of kidney years between 5 – 10 years of having kidney stones. 80% of the population are known to develop calcium stones, 5 to 10 % develop uric acid stones, and 10% develop struvite stones. A rare genetic disorder called cystinuria is found in about one in every 7000 people, mainly under the age of 40 [9].  

Pathophysiology 

Waste products within the urinary system, mostly made up of calcium salts and, occasionally, uric acid or amino acids called cystine, form crystals that become kidney stones [1]. The pH level in one’s urine is an essential indicator for stone formation. Most kidney stones form at the junction of the nephron, collecting tubules and renal pelvis as Randall plaque. Randall plaque is a substance that contains calcium phosphate, which is a by-product of repeated contact with urine and forms calcium oxalate layers that can grow into varying sizes. 75% of kidney stones comprise calcium oxalate crystals, making it the most common type [7]. 

Kidney stones are usually less than 5mm and sometimes pass with urination. Kidney stones greater than 7mm require surgical intervention [4]. 

Types of Kidney Stones 

• Calcium stones: There are two kinds of calcium stones: calcium oxalate and calcium phosphate. [6, 8] 

• Calcium oxalate is the most common type of kidney stone which combines with oxalate in the urine. These can form from foods high in oxalate, such as rhubarb, spinach, nuts, wheat bran, and peanuts, animal protein, such as meat, cheese, and milk, and foods high in sodium. 

• Calcium phosphate stones are the least common and form well at lower pH levels. Kidney stones formed from calcium are usually due to excess calcium not utilized by the bones and muscles, which is flushed in the urine and combined with other waste products to form kidney stones. Calcium phosphate stones can develop when one eats a diet high in sodium and animal protein, such as red meats, fish, and shellfish. 

• Uric stones (acid) – form due to a diet high in purine, converted into uric acid in the body. Purine is contained in food, processed meats, and shellfish. Other causes of increased formation of uric acid are type two diabetes, obesity, and metabolic syndrome. Uric acid can also be hereditary. Chemotherapy treatment for disease processes like leukemia or lymphoma can lead to the formation of uric acid stones due to the sudden lysis of millions of cells that contain purines. Potassium citrate is considered the 1st line of treatment and not allopurinol for gout. 

• Struvite stones form from urease and upper urinary tract bacterial infections (chronic stones). Struvite stones are commonly seen in women with chronic indwelling urinary catheters and susceptibility to Proteus mirabilis. They can form suddenly and be significantly large, which is referred to as Staghorn stones [1,8].  

• Cystine stones Form due to an intrinsic metabolic defect that causes a natural product known as cystine to leak in the urine due to the failure of reabsorption in the renal tubules due to the bonding of two molecules of amino acid. Cystinuria is a rare hereditary condition. Less than 3% of the population develops this type of stone [1].  

Clinical Manifestations 

The sudden onset of severe colicky pain that radiates to the flank, groin, or abdomen is the classic clinical manifestation of nephrolithiasis. Some patients are asymptomatic, and kidney stones are found accidentally during imaging of other conditions. Complications of nephrolithiasis may include the following: acute kidney injury, infection, and obstruction that causes urinary retention.  

The type of pain the patient experiences depends on the location of the stones. The intensity or location of pain may change as kidney stones migrate. Renal calculi in the lower urinary tract can cause urinary frequency or urgency [3, 6]. 

Obstruction caused by kidney stones may cause urinary frequency and dysuria, urosepsis, fevers, chills, colic pain, nausea, and vomiting. 

Other symptoms of kidney stones include: 

• Gross hematuria and microscopic hematuria are found in 85% of patients. 

• Hydronephrosis  

• Discomfort proximal to the kidneys.  

Diagnostic Testing 

It is important to obtain a history and physical exam, including imaging. A differential diagnosis for patients with acute colic pain is necessary to rule out other conditions, such as acute abdominal or gynecological conditions, that may have similar clinical presentations as those with calculi [1,6].  

• CT scan is the gold-standard tool for confirming renal calculi in acute flank pain.  

• Ultrasound is used to detect the stones’ size and is the first line for pregnant patients.  

• Abdominal X-Ray (KUB): This test can be used in conjunction with a CT scan to assist with identifying non-calcified stones by determining the level of obstruction and the presence of hydronephrosis.  

• Urine and blood work 

• Urinalysis is performed to rule out hematuria and pyuria (white cells).  

• The urine culture and multiplex polymerase chain reaction test (PCR) are used to detect infection and conduct drug sensitivity studies.  

• Assessment can rule out infection and check pH, uric acid, and calcium levels. 

• A serum kidney function test is used to help determine any effects on the kidney’s function. 

• Serum parathyroid hormone levels as hyperparathyroidism may lead to kidney stone formation due to increased calcium levels.  

Treatment 

There are several treatment options for kidney stones. The treatment of kidney stones is mostly dependent on the size, intra-renal location, and the type of stone that a patient may have in their body.  

Small kidney stones can pass on their own through the urinary tract system and do not require any treatment. Sometimes, healthcare providers may provide patients with a unique collection container to capture kidney stones. Possible kidney stones can be sent to a lab to identify the type of stone [6, 10]. 

• Shock wave Lithotripsy: Extracorporeal shock wave lithotripsy. Small stones involve blasting kidney stones into small pieces, which are then allowed to pass through the urinary trap system. This is usually an outpatient procedure and requires anesthesia [6]. 

• Ureteroscopy and cystoscopy: Ideal for renal calculi that is distal e.g. mid-ureteral calculi. Rigid and flexible ureteroscopes in conjunction with graspers and baskets are used. Ultrasonic, electrohydraulic, and laser equipment are used to fragment stones. Stents may also be placed to keep the ureters patent [6,8].  

• Percutaneous nephrolithotomy – This involves the insertion of the direct to into the kidney through a small incision that is made in the back where the kidneys are located. When the kidney stones are larger, the health provider may use a laser to break the kidney stones into smaller pieces. This procedure is performed under general anesthesia. With this procedure, the doctor may use your stents in the urinary tract system to help maintain the floor of urine or to aid with the passing of a kidney stone [8]. 

• Pain management: Most patients experience pain due to kidney stones, which can be managed with ibuprofen and sometimes narcotics. Caution must be used with Non-Steroidal Anti-inflammatory Drugs, as they can affect renal function and decrease black flow obstruction. Renal colic pain that is intractable can be effectively managed by decompressing the obstruction using a percutaneous nephrostomy or ureteral stent [6].  

• Observation: If patients with renal calculi less than 5 mm are asymptomatic, they can be observed over time for renal deterioration stone growth. In this case, patients are encouraged to catch any stones present with a strainer and submit them for analysis to determine the composition of the stone.  

• Potassium citrate can be given to patients with recurrent stones and abnormal metabolic disorders [5, 6]. 

Medication Management Used for the Different Types of Renal Calculi [6] 

Calcium Kidney Stones 

These may be treated with potassium citrate, which could assist with increasing the amount of citrate and pH levels in the urine and could be used in conjunction with a diuretic.  

Uric Acid Stones 

These could be treated with allopurinol and potassium citrate, which help reduce the amount of uric acid in the body by dissolving it. This can also help alkalize the urine pH to at least 6.5. 

Struvite Stones 

These can be prevented by treating urinary tract infections with antibiotics such as acetohydroxamic acid and long-term antibiotics. These stones are formed due to chronic urinary tract infections.  

Cystine stones 

This type is commonly treated with Mercaptopropionyl glycine – antioxidant and potassium citrate.  

Alpha-blockers, such as tamsulosin, are used for small stones. They relax bladder muscles to assist with the passing of stones, letting them pass.  

Patient Education 

• Educate patients on symptoms to watch out for, especially with recurring kidney stones.  

• Counsel patients on the importance of staying well hydrated, up to 3 – 4 liters per day, to achieve a urine output of 2.5 L per day, especially during the acute phase of kidney stones. Also, patients must be encouraged to limit their intake of coffee, tea, alcohol, and grapefruit juice.  

• Counsel patients on exercises such as Sauna hot yoga and heavy exercise could also lead to kidney stones due to the loss of water through sweating due to the activity [8] 

• Instruct patients to use a filter for urine – Stones must be sent to the lab for analysis. 

• Patients with calcium stones must be counseled to limit sodium intake and consume calcium between 1000 to 1200 mg per day. 

• Counsel patients on the importance of maintaining a healthy diet and weight: Patients with calcium oxalate stones must be encouraged to limit foods high in oxalate, such as chocolate, rhubarb, wheat bran, cranberries, nuts, and beans. Reduce the intake of foods high in purine as this could lead to an increase in uric acid which aids in the formation of uric kidney stones. Examples are red meat, alcohol, anchovies, shellfish, organ meat, and sardines. 

• Patients with uric stones and calcium stones must limit foods high in animal protein.  

• Counsel patients on the importance of consuming low sodium intake.  Increased sodium intake causes more excretion of calcium in the urine as the two electrolytes share the same transportation 

• Reduce sweetened beverages, especially those high in fructose corn syrup. 

• Offer Thiazides to patients with high calcium and recurrent stones.  

Conclusion

A detailed history helps determine directed therapies for patients with risk factors for developing kidney stones, which are becoming more common. A nephrology consult may be helpful with patients with chronic kidney stones to prevent the formation of new kidney stones and preserve renal function. This must include patient education to help prevent recurrences of kidney stones.  

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