Case File: Flank Pain in Month Five

Why is the risk of kidney stones higher in spaceflight?

• Bone loss releases calcium, which is excreted in the urine [1][2].
• Less urine. In long-duration crew, urine volume was 47% lower before flight day 30 and 39% lower after flight day 60 [1].
• Urine chemistry. Supersaturation of stone-forming salts (brushite and calcium oxalate) rose during flight [1][2].
• A prior symptomatic stone is a clear personal risk factor [1].

How would the diagnosis be made on board?

With ultrasound, which is NASA’s in-flight diagnostic tool for this problem [1]. A non-physician crewmember can obtain usable images when guided in real time by experts on the ground. See point-of-care ultrasound. Look for:

• a visible stone at the junction of kidney and ureter or in the renal pelvis;
• swelling of the collecting system on the painful side (hydronephrosis), if enough time has passed for it to develop;
• a missing urine jet into the bladder from the ureter on the painful side [1].

NASA notes an open question: whether ultrasound criteria work the same way in flight. For example, cabin carbon dioxide may weaken the “twinkle” artifact used to spot stones [1]. On Earth, never delay a clinically needed CT scan; if he were on the ground with a suspected infected, blocked kidney and a non-diagnostic ultrasound, CT would be appropriate.

What is the key management decision?

First, treat. Medicines on the International Space Station for this problem, per NASA’s 2024 evidence report, include [1]:

• Pain: ketorolac and ibuprofen (anti-inflammatory drugs, or NSAIDs), and hydromorphone (an opioid).
• Nausea: ondansetron and promethazine.
• Stone passage: tamsulosin.
• Infection: antibiotics such as trimethoprim-sulfamethoxazole.

European urology guidance makes an NSAID the first drug of choice and an opioid the second choice [3]. Ketorolac is contraindicated in advanced kidney impairment and in people at risk of kidney failure from volume depletion, so correct dehydration first [4]. Tamsulosin helps mainly with larger stones: in a meta-analysis of randomized trials, it improved passage of 5–10 mm stones (number needed to treat 5) but not smaller ones; pooled passage was 85% vs 66% overall [5][3]. Do not force fluids during acute colic. A Cochrane review found no reliable evidence that high-volume fluids help stones pass [6]. Give fluids to replace what he has lost through vomiting.

Then decide: manage on board, or decompress? On Earth, these findings mean urgent drainage of the kidney (a ureteral stent or a nephrostomy tube) [3]:

• fever or other signs of infection with a blocked kidney (a urological emergency: drain urgently and start antibiotics immediately) [3];
• a blocked solitary kidney, both sides blocked, little or no urine, or rising creatinine (kidney function failing) [3];
• pain or vomiting that cannot be controlled [3].

Nitrofurantoin is not a treatment for a kidney infection: European guidance says not to use it for pyelonephritis [7]. In low Earth orbit, any of these findings means evacuation for definitive care on Earth [1][8]. On a Mars mission there would be no evacuation, so ultrasound and drugs on board must be enough [1].

Research gaps, not current capability:

• Ultrasonic propulsion (pushing a stone with focused ultrasound): stones moved in 14 of 15 people in a first human trial; NASA rates the technology readiness level at 5–6 [9][1].
• Percutaneous nephrostomy (a drain placed through the back into the kidney): NASA notes evidence for autonomous use in flight is thin; in low Earth orbit the condition would likely lead to evacuation [1].

For context: NASA reports no symptomatic kidney stones in U.S. ISS crew to date, and one possible episode in a cosmonaut [1].

How could this have been prevented?

• Fluids. Stone risk rises when urine output falls below 1.5 L a day. A NASA model suggests in-flight water intake would need to rise to about 3.2 L a day to bring calcium oxalate risk back to preflight levels [1]. That is a prevention target; during acute colic, give fluids only to replace losses [6].

• Potassium citrate. In a flight study of 30 crewmembers, 20 mEq a day reduced calcium oxalate risk markers [10].

• Diet. Limit sodium and animal protein [1].

• Protect bone with resistance exercise, which reduces the calcium released into urine [1].

• Screen the urine before flight. NASA assesses crew with a 24-hour urine stone-risk profile, NASA’s Renal Stone Risk Index (RSRI). In a retrospective review, a high RSRI correlated strongly (0.93) with known stone-formers; NASA performs it annually and after flight [1].

With his stone history, a preflight urology review and 24-hour urine test would have been reasonable; see kidney stone risk.