Army Aviation

Kidney Stones

Ask the Flight Surgeon / By MAJ Sonya Horwell, MD: Q: I had kidney stones before and I never want to have them again. What are they? What can I do to prevent them from ever happening again? Why do I have to go through more evaluations to get a waiver if they passed already?


FS: Kidney stones are a common medical condition affecting 1 out of 11 people and are composed of naturally-occurring substances in the body: calcium, oxalate, cysteine, or uric acid. These chemicals can crystallize in the urine and become large in size, resulting in a kidney stone. It is not uncommon for these stones to form in the kidney without causing symptoms; but on occasion, the stone will move from the kidney and enter the urinary tract. A stone may only be a few millimeters in size, but can cause exquisite pain, bloody urine, nausea and vomiting or urinary urgency (when you feel the sudden urge to urinate but may not be able to urinate or only urinate a small amount). Small stones will pass naturally in about a week, but larger stones may require a medical procedure to facilitate the process.

There are several factors that influence the formation of stones. Crewmembers with a personal or family history of kidney stones are at increased risk of forming stones. The following dietary factors are known to increase the likelihood of developing kidney stones: decreased fluid intake, low dietary calcium, high levels of animal protein, high levels of sugars like sucrose or fructose, low levels of phytate (wheat, rice, rye, barley, and bean products), high sodium diet, and high spinach consumption. Medical conditions can also place the patient at higher risk for developing kidney stones. Some common conditions associated with stones are obesity, gout, diabetes mellitus, gastric or intestinal bypass surgery, primary hyperparathyroidism, and Crohn’s disease.

What can I do to prevent them from ever happening again?
The answer depends on what substances the stone is composed of and if you have any underlying medical conditions that predispose you to form kidney stones. When passing a stone (e.g. having symptoms described above), see your doctor to ensure the diagnosis is correct. After confirmatory testing, your healthcare provider may complete other lab work to see if you have a medical condition, such as diabetes mellitus, that puts you at higher risk for stones to form. Proper management of associated conditions is needed to minimize their impact on stone formation. Your doctor will likely give you a strainer to filter your urine each time you urinate until you pass the stone with the goal of collecting the stone for analysis. This is another important step in preventing stones in the future. If you can find out the composition of the stone, then the doctor can make suggestions on how to modify your diet or prescribe medicines that target the particular chemical composition of the stone. One of the simplest steps you can take is to stay hydrated with water; two liters of urine per day is the goal. This will lower the urine concentration and prevent crystallization.

Why do I have to get a waiver if they passed already?
Kidney stones can be exquisitely painful, distracting and therefore incapacitating in flight. It is important that the Army’s Aeromedical Authority (AAMA) ensures you had the appropriate workup for the kidney stones, even if they are just in the kidneys and you haven’t passed one yet (e.g. they were found on a CT scan of the abdomen you may have had for other reasons). It is also important that AAMA is aware that you are doing the appropriate actions (i.e. staying hydrated, taking medicines if needed to lower your risk of stone formation, maintaining good control of medical conditions that can increase your risk of stone formation) to lower your risk of stone formation. You are an essential part of the aircrew. If you are unable to perform your duties, you jeopardize the lives of all personnel in the aircraft as well as those on the ground. AAMA needs to know that you and your medical team are appropriately mitigating the risk of your condition to feel comfortable enough to have you as part of the aircrew. A single stone with no abnormalities found during the medical workup can be noted on the annual physical and does not need a waiver. A history of multiple stones is usually granted a waiver if the criteria listed in the aeromedical policy letter is met.

If you are dealing with kidney stones, talk with your healthcare provider. This will allow for treatment to start and the waiver process to begin.

If you have a question you would like addressed, email it to This email address is being protected from spambots. You need JavaScript enabled to view it.; we’ll try to address it in the future. See your unit flight surgeon for your personal health issues. The views and opinions offered are those of the author and researchers and should not be construed as an official Department of the Army position unless otherwise stated.

MAJ (Dr.) Sonya Horwell is a flight surgeon at the U.S. Army School of Aviation Medicine, Fort Rucker, AL.