Oh the stone . . . kidney stones suck for a number of reasons.
1—>They hurt a lot
2—> They hurt a lot
3—> They hurt a lot
4—> You can get them again

The biggest threat from kidney stones occurs if they obstruct the ureter and an infection develops behind the stone. That is what is known in the parlance of our times as an "infected stone” or "pus under pressure."

This brings up an interesting fact, there are some kidney stones that are caused by a baseline infection: struvite stones. Struvite stones are generated by bacteria in the kidneys who create urase, and from some magic of chemistry that tends to create large kidney stones. All of theses struvite stones are bacteria infested, but not everyone with struvite stones becomes septic.  Other kidney stones can also get infected (any of the calcium or uric acid stones) if they pick up bacteria from an infection of the bladder that starts creeping up the ureters to the kidneys.

The acute risk for developing sepsis from an “infected stone” is not only because there are bacteria hanging around the kidney stone, the real problem develops when the kidney stone blocks the ureter and then the urine above the stone gets infected. Generally, as long as there is urine moving around the infected stone, the risk for sepsis is low. In fact, one of the ways that urologist treat infected stones is to place a stent in the ureter. They don’t take out the infected stone (this can damage the ureter and allow bacteria to escape into the rest of the body), the stent just allows urine to flow around the stone while the patient is treated with antibiotics. This is why a urologist may not place a stent or perc-neph tube in a patient with an infected, but not obstructive, stone.

The evaluation of an obstructing and infected stone can be tricky. If the stone is completely obstructing, all of the infected urine can be sequestered behind the stone, so the UA may be absolutely clean. If the other kidney is working well it can up its filtration capacity and your creatinine can be normal. But the patient will usually be telling you they are sick—>pain, fever, hypotension. Their labs generally have an elevated WBC and CRP.  It can be challenging, because all kidney stone patients look horrible when they first present, but pay attention to the persistence of symptons when you are evaluating a patient for a possible infected stone.

Imaging: CT scans can show signs of obstruction and infection.  Ultrasound of the kidney may show hydronephrosis, but you cannot always see the stones themselves. We can also get an ultrasound of the bladder that looks at ureteral jets. The jets are the urine being squirted into the bladder by the ureter. The science is still evolving on this, but the take home is that obstructing stones change the flow of the ureteral jets by either decreasing the velocity of the jet or turning the jet into a low level constant flow rather than a definite squirt.  (It is convenient that you can compare the affected side to the unaffected side in the same bladder.) Also, if you see symmetric jet velocity/frequency the chance there is an obstructing/infected kidney stone is dramatically lowered—>the patient likely does not need emergent surgery.

There are a lot of pieces of the puzzle to put together for these patients. If there is any concern about an infected/obstructing kidney stone get urology involved early, and start antibiotics early, because the patient can get very sick, very fast.


Jandaghi AB1, Falahatkar S, Alizadeh A, Kanafi AR, Pourghorban R, Shekarchi B, Zirak AK, Esmaeili S. Assessment of ureterovesical jet dynamics in obstructed ureter by urinary stone with color Doppler and duplex Doppler examinations. 2013 Apr;41(2):159-63. doi: 10.1007/s00240-012-0542-7. Epub 2013 Jan 5.

Marien T, Miller NL. Treatment of the Infected Stone. Urol Clin North Am. 2015;42(4):459-472.

Burge HJ1, Middleton WD, McClennan BL, Hildebolt CF. Radiology. 1991 Aug;180(2):437-42. Ureteral jets in healthy subjects and in patients with unilateral ureteral calculi: comparison with color Doppler US.