Wondering if a Urine Infection can lead to Kidney Stones? Have a read!
Kidney stone clinic in Chennai has seen kidney stones as an increasing clinical problem in both children and adults. Kidney stone is so common that it is experienced by one in ten individuals, yet the mechanisms responsible for urinary stones is not understood. Urine infection caused by bacteria have long been recognized to contribute to struvite urinary stones. A possible association between kidney stones and the high rate of urinary tract infections (UTI) in urinary stone patients and multiple case series of culture-positive urinary stones, including calcium oxalate and calcium phosphate stones have been indicated in several findings. However, urine infection as a causative factor in the development of the more common calcium oxalate and calcium phosphate stones has not been firmly established.
Struvite stones form due to urinary infection
Supersaturation, a process by which the concentration of substances like calcium and oxalate present in urine, exceed the limits of their solubility is known to be the key component in kidney stone formation. However, individuals with and without kidney stones exhibit considerable overlap in urine chemistries. Also, supersaturation with calcium oxalate or calcium phosphate is not different from controls when compared in case studies of recurrent stone disease. Thus, it is observed that supersaturated urine may be the highest risk factor, but it is by itself not sufficient to process stone formation. This is further supported by the fact that treatment with dietary modifications, increased fluid intake, citrate salts and/or thiazide diuretics to reduce urine calcium oxalate supersaturation only moderately controls recurrence rates. Prevalence of kidney stone disease among adults and children has increased despite these treatment strategies. There is critical need to identify other factors that contribute to pathogenesis of kidney stone formation. Kidney stone disease contributed by urinary bacterial infection has long been recognized. Struvite stones composed of magnesium-ammonium-phosphate is a conglomeration of bacteria, crystals and protein matrix that form due to urinary tract infection (UTI) caused by urease-producing bacteria. However, only 4% of all kidney stones are struvite. Whereas, calcium oxalate stones form more than 60% of kidney stones and calcium phosphate stones contribute to more than 40%. The observation is that there is emerging evidence indicating contribution of bacteria to the formation of calcium oxalate and calcium phosphate stones.
Urine infection has been implicated in the formation of kidney stones
The incidence of kidney stones has been increasing worldwide with up to 14% prevalence during a life time. There has been a corresponding rise in the treatment for kidney stones associated with urine infection. Recent data suggests that the application of ureteroscopy to get rid of kidney stones has significantly risen over the last two decades compared to other treatment modalities. Though percutaneous nephrolithotomy is the treatment of choice for larger struvite stone removal, smaller stones associated with urine infection may be better treated with less invasive techniques, such as laser lithotripsy available at kidney stone clinic in Chennai. Cases of UTIs associated with kidney stones, including those with a positive urine culture or recurrent infections, form a nidus for infection and hence warrant stone removal treatment. Presentation of kidney stone associated with urinary sepsis require immediate surgical decompression and post the infection being resolved, has to be followed by an elective planned stone removal. Outcomes of ureteroscopy and stone treatment for patients with positive urine culture or recurrent UTIs have to be reviewed and evaluated to know whether the infection has resolved with the clearance of stones. Thus, the implication of urine infection in patients with kidney stone formation often needs complete eradication of stones for clearance of their urine infection.
Mechanisms by which urine infection may contribute to kidney stones
If urine infection by bacteria do contribute to formation of calcium oxalate stones, one of the potential mechanisms could be the possibility of bacteria getting adhered to crystals. Findings support this mechanism where some bacteria selectively accumulate over certain crystal types and an increased number of crystal-crystal agglomerations is found in the presence of these bacteria. Increased bacterial aggregation was noted around Calcium oxalate monohydrate crystals as compared to calcium oxalate dihydrate and control silicon dioxide crystals, with similar results in other studies as well. In a similar study, it was demonstrated that E. coli and other bacteria like Klebsiella pneumonia increased the number of Calcium oxalate crystal aggregates compared to blank or intact red blood cell control. Another possibility for urine infection that could contribute to kidney stone is bacterial production of citrate lyase, which could lower the urine citrate levels that lead to supersaturated urine and crystal formation. This potential mechanism has been supported in the finding that demonstrates mean urine citrate to be 2-fold lower in 17 standard urine culture-positive patients compared to 30 standard urine culture-negative patients. Last possible mechanism demonstrates the ability of bacteria-crystal aggregates to bind to the tubular epithelium establishing expression of stone matrix proteins in either renal tubular epithelium or inflammatory cells. The component that, at least in part, that is expected to differentiate crystalluria from progression to stone formation are the stone protein matrix.
Urologists face a specific challenge in the management of patients with recurrent urine infections which is defined as three or more UTIs in a year or two or more UTIs in 6 months along with asymptomatic non-obstructing kidney stone. Stone removal is often advised for such patients at kidney stone clinic in Chennai, with the precaution that the stone may act as a nidus for recurrent infections.
UTI and USD occur in the same patients
In a whole population survey of Taiwan, a UTI history was the most common associated condition in children with newly diagnosed USD (22). Overall, 34% of children (44% of females and 24% of males) diagnosed with USD had a history of UTIs (22). In contrast, the reported childhood UTI prevalence is only 8% (23). The association between UTI and USD extends into adulthood. For example, in a retrospective review of 1,325 adults admitted for USD to a Swedish hospital over a 7-year period, 28% had a positive standard urine culture
