Working through controversies: The 24-hour urine test
Controversies muddy kidney stone medical management. One is the importance of the 24-hour urine collection, which helps to guide stone treatment and management, experts say.
“One of the essential things to do is a 24-hour urine—in my opinion, ideally two 24-hour urines. Yet, if you look at the data nationally, probably less than 10% of our stone formers are getting the appropriate metabolic workup,” Dr. Wood said.
It’s one thing to order the test; it’s another to have patients complete it correctly for accurate results.
“In reality, if we’re going to be ordering the 24-hour urine, we have to be willing to spend time with patients to discuss accuracy and compliance,” Dr. Wood said. “We recently published an article [in Urology Practice, Jan. 1, 2019] looking at our compliance rates. Even though we order the test, our compliance rate was only about 50%, meaning half the people weren’t performing the studies that we were ordering.”
Dr. Wood said a slight change during the study brought up the compliance rate.
“We basically did the paperwork for our patients so they would get the 24-hour urine kit sent to their houses. That increased our compliance from 47% to 65%,” he said.
Dr. Wood and colleagues also published an examination of the accuracy of the 24-hour urine test in stone formers (Rev Urol 2018; 20: 119–24). That study found that even though patients receive the kits, many don’t use them properly. One solution is patient education, including time spent with patients, handouts, and take-home instructions.
Medical management best practices
Dietary recommendations are an important part of the medical management of stone disease, but the approach shouldn’t be cookie cutter, according to the experts interviewed for this article.
“Volume is probably the single most commonly recommended dietary change—just increasing fluid intake. That’s primarily because the more dilute the urine, the lower the concentration of the minerals, the less driving force there is for stone formation,” Dr. Pearle said.
Dr. Matlaga said the goal is to achieve a urine volume of about 2 liters a day by drinking at least 2 liters of fluids daily. Some of his patients are using wearable devices help them accomplish the task.
“For example, there are now smart water bottles that can link to smartphones, and they can help make sure patients consume their target fluid consumption,” Dr. Matlaga said. “I think we’re starting to see the use of technology helping support some of these dietary and lifestyle changes.”
There are, however, controversies around which fluids, other than water, are best. Findings of some epidemiologic studies are at odds with small metabolic studies looking at various fluids, according to Dr. Pearle.
Large cohort epidemiologic studies, she said, suggest coffee, tea, beer, wine, and orange juice are associated with reduced risk for first-time stone formation, while sugar-sweetened beverages are associated with an increased risk. A randomized trial looking at the effect of soft drinks found an increased risk of stones with soft drink consumption based primarily on phosphoric acid-based soft drinks rather than citric acid-based soft drinks (J Clin Epidemiol 1992; 45:911-6). Metabolic studies examining fruit juice consumption have found orange juice consistently shows a benefit in stone formers because it provides alkali in the form of potassium citrate.
“There is a lot of controversy about lemonade, despite general interest in the the community for lemonade consumption as a stone prevention measure. There have been metabolic studies that have not shown a benefit of lemonade. People have looked at other juices as well with mixed results,” Dr. Pearle said.
Generally recommended dietary measures for kidney stone patients include maintaining a normal calcium intake and limiting salt intake and animal protein.
While the value of limiting animal protein is controversial, metabolic studies have shown that animal protein is a risk factor for stone formation because it increases urinary uric acid. Uric acid binds to inhibitors of stone formation, reducing inhibitory activity in the urine. Animal protein also provides an acid load, which lowers urinary citrate and urine pH, according to Dr. Pearle.
“Despite mixed evidence, we generally recommend limiting animal protein intake to no more than two servings a day,” she said.
In patients with low citrate in urine, Dr. Pearle recommends increasing fruits and vegetables, which are high in alkali. Alkali drives citrate into the urine.
Oxalate restriction is highly controversial among urologists.
“There is strong data to support a significantly increased risk of kidney stones in people with increased oxalate and increased urinary oxalate excretion. The biggest issue is there is a lack of good data on what foods to restrict and what foods to avoid,” Dr. Wood said.
Research to date suggests patients who are high in oxalate should avoid spinach and potatoes. Dr. Wood also recommends patients refer to the Harvard database of dietary oxalate content for other foods high in oxalate (bit.ly/oxalate-Harvard).
Oxalate restriction in patients who don’t have an oxalate problem might not be necessary, according to Dr. Wood. Urologists can confirm whether oxalate is a driver of a patient’s stone disease with a 24-hour urine collection.
Dr. Pearle said she recommends at least modest restriction of foods high in oxalate, but it’s a balance if those foods are part of an otherwise healthy diet.
“Things like nuts and whole grains, beans, beets, and potatoes are all high in oxalate, so a lot of people who are healthy eaters can have very high urinary oxalate. If the oxalate is very high, it is reasonable to recommend being careful about oxalate intake, but at least from my standpoint, in patients with a normal urinary oxalate, I don’t generally focus on oxalate too much,” Dr. Pearle said.
Next: What about medications?