Clinical Education Center
Kidney Stones — Understanding Risk, Reducing Recurrence
Kidney stone disease, also known as nephrolithiasis or urolithiasisis, is one of the most painful and prevalent urological disorders. Each year in the United States, kidney stones account for approximately three million visits to health care providers, and for over one million emergency room visits.1, 2
Because the causes and types of kidney stones vary, accurate diagnosis plays an important role in directing therapy and long-term patient management. Dr. Powers Peterson, Medical Director, Quest Diagnostics Nichols Institute, Valencia CA, discusses the complexities of the condition and explains how defining an individual’s risk profile for stone formation is a first step to reducing the likelihood of recurrence.
“There are two important facts for doctors and the general public to know about kidney stones,” says Dr. Peterson. “First, it’s a common disorder, experienced by at least one in twenty people during their lifetime.3 Second, there are now assays available, which help physicians better define the kind of kidney stone and therefore help guide effective treatment and management of the disorder. This is particularly important given the extremely painful nature of the condition and the fact that those who experience it once have a 50% chance of recurrence.”
Stone formation occurs due to an imbalance between mineral salts and crystal growth inhibitors in the urine and a patient’s level of hydration. The cause of imbalance may be hereditary (e.g. hypercalciuria), related to another medical condition (e.g. gout), a chronic urinary tract infection, or it may be unknown.
The most common types of stone contain calcium in combination with oxalate or phosphate. Other types of stones include those caused by infection in the urinary tract, called a struvite or carbonate apatite, as well as urate stones, cystine stones and stones formed by a combination of chemicals.
Diagnosing a kidney stone includes an initial evaluation based on family history, associated medical conditions, medications, and diet; biochemical blood studies; urinalysis; X-rays; analysis of the stone itself, if obtained. It also typically includes 24-hour urine collection to analyze volume, pH, calcium, magnesium, phosphate, oxalate, urate, creatinine, sodium, citrate and cystine.
Tests are available to determine the stone type, and thereby guide treatment and long-term patient management. “Profiles, such as UroRisk® and Stone Risk®, provide a metabolic picture of why an individual produces a stone,” explains Dr. Peterson. The first goal is to determine whether or not the stone is infection-related. “We are clearly going to proceed differently with someone who has an infectious etiology compared with someone who, for instance, has gout. Treating non-infectious stones will invariably involve some form of dietary manipulation, in particular increasing water intake.”
Dr. Peterson illustrates the importance of making this distinction by reference to pneumonia. “If you have pneumonia, we do a culture to try to determine whether the offending agent is a virus or a bacterium. This in turn will direct treatment – preferably the most specific therapy with the least potential for complications. Similarly, once we’ve identified that the patient has a stone, the goal is to determine exactly what’s causing it, so we can manage the problem in the least offensive way to the body. Everybody understands the difference between a viral and bacterial pneumonia and to some extent this is similar. An infection-related condition determines one course of action, while a metabolic problem establishes the need for a different therapeutic agent.”
Specimen Collection & Testing
Quest Diagnostics offers several different kidney stone risk assessment profiles to guide initial treatment and long-term patient management. They are all based on a 24-hour urine collection, which Dr. Peterson stresses, is a significant pre-analytical variable that influences test result accuracy. Compliance with collection instructions is, therefore, highly important. Collection in the special container provided with rigorous attention to the details of vigorous mixing, filling and capping the specimen vials, and labeling, are all important factors to ensure accurate test results. Those patients who have a urine output greater than 3.8 liters/day, for example, some diabetic patients, will require more than one collection kit.
All patients are encouraged to drink large amounts of water to assist in passing the stone. Additional treatment options depend on the degree of obstruction, kidney function, presence of infection, pain and bleeding. Non-invasive procedures are used in most cases. Lithotripsy, the pulverizing of the stone by shock waves, is the most common of these. Open surgery is used in rare, complicated cases.
Long-term Patient Management
Based on the Stone Risk® and UroRisk® test results, a diagnostic profile for the patient is generated based on a 24 hour urine collection. This graphically shows the patient’s level of risk for stone formation based on chemical levels and urine saturation. “Whether a patient is high on chemical A and low on chemical B will guide the physician in selecting treatment options,” says Dr. Peterson. “What we’re looking at here are urinary risk factors for kidney stone formation, based on the patient’s levels of a particular chemical, such as calcium or magnesium. In addition, these graphical reports will show relative supersaturation values.”
Dietary modification is an important component in reducing the risk for stone recurrence. The mainstay of this is increasing fluid intake, especially of water. Avoiding certain foods (meats, salt, certain vitamins, chocolate, dairy products and others), while increasing consumption of others (citrus fruit) are also options depending on the patient’s profile.
“This approach is exemplified by the way we treat gout, a disease that’s been known for centuries,” notes Dr. Peterson. “While we don’t always know why some people have gout, our objective is to modify their diet to reduce the level of purine analogs they produce. These lead to high urate concentrations in the blood, which then precipitate out in the kidney.”
In some cases, therapies may be required and, depending on the chemical composition of the stone,may involveacidifying or alkalinizing the urine. For cystine stones, the pH of the urine should exceed 7.5. For struvite stones, the goal of therapy is to acidify the urine to counteract the alkalinization induced by Proteus species’ formation of ammonia. For patients with uric acid stones, alkalinization of the urine is appropriate.
Repeat testing is usually performed to monitor the effectiveness of the intervention and the patient’s adherence to the recommended regimen.
- Urological Diseases In the United States. National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC). http://kidney.niddk.nih.gov/statistics/uda/Urolithiasis-Chapter08.pdf Accessed on September 12, 2012.
- Foster G, Stocks C, Borofsky S. Emergency Department Visits and Hospital Admissions for Kidney Stone Disease, 2009. Healthcare Cost And Utilization Project Statistical Brief #139. July 2012. Agency For Healthcare Research and Quality (AHRQ)
- National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC). U.S. Department of Health and Human Services.http://kidney.niddk.nih.gov/Kudiseases/pubs/stonesadults Accessed.11/19/2012 5:40:12 PM]