Nephrolithiasis (also known as urolithiasis, renal calculi, or kidney stones) is exceeded in frequency as a urinary tract disorder only by infections and prostatic disease. Calcium salts, uric acid, cystine, and struvite are the basic components of most kidney stones in the Western Hemisphere. Calcium stones constitute more than 70 % of all kidney stones. It has been suggested that there are metabolic as well as environmental risk factors that render urine more conducive to crystallization, thus resulting in an increase risk of stone formation. Metabolic and environmental profiling involves studies used to ascertain these risk factors of nephrolithiasis. These clinical and laboratory tests usually entail measurements of a number of blood and urine parameters, including estimates of urine state of saturation with calcium and uric acid salts, net gastro-intestinal alkali absorption, renal threshold of phosphate and other renal clearances, as well as net acid and total nitrogen excretions.
Although there are published studies on metabolic and environmental profiling, the value of these tests in the management of patients with kidney stones is still questionable. Additionally, there are factors other than urine composition that may play a role in stone formation. Furthermore, there is a lack of data to show that metabolic and environmental profiling improves the health outcomes of patients with kidney stones. Although guidelines on urolithiasis from the European Association of Urology (Tiselius et al, 2006) include metabolic profiling, they state that there is "no absolute consensus that a selective treatment is better than a non-selective treatment for recurrence prevention in idiopathic calcium stone disease", and note that an analysis of data from the literature has suggested only a slight difference in favor of treatment directed towards individual biochemical abnormalities.
The significance of urolithiasis screening is controversial. In a review on the clinical and cost effectiveness of CT and MRI for selected clinical disorders, the Canadian Agency for Drugs and Technologies in Health (CADTH) reported that no clinical or economic evidence was found on the use of CT and MRI for screening urolithiasis. CADTH concluded that the use of CT or MRI for this indication should be considered investigational (Murtagh et al, 2006).
Dhar and Denstedt (2009) stated that imaging has an essential role in the diagnosis, management, and follow-up of patients with stone disease. A variety of imaging modalities are available to urologists, including conventional radiography (KUB), intravenous urography (IVU), ultrasound (US), magnetic resonance urography, and CT scans, each with its advantages and limitations. Traditionally, IVU was considered the gold standard for diagnosing renal calculi, but this modality has largely been replaced by un-enhanced spiral CT scans at most centers. Renal US is recommended as the initial imaging modality for suspected renal colic in pregnant women and children, but recent literature suggests that a low-dose CT scan may be safe in pregnancy. Intra-operative imaging by fluoroscopy or US plays a large part in assisting urologists with the surgical intervention chosen for the individual stone patient. Post-treatment imaging of stone patients is recommended to ensure complete fragmentation and stone clearance. Plain radiography is suggested for the follow-up of radiopaque stones, with US and limited IVU reserved for the follow-up of radiolucent stones to minimize cumulative radiation exposure from repeated CT scans. Patients with asymptomatic calyceal stones who prefer an observational approach should have a yearly KUB to monitor progression of stone burden.
Shiekh and associates (2009) noted that although much has been learned regarding the pathogenesis of kidney stones, the reason(s) why some individuals form stones while others do not remains unclear. Nanoparticles, which have been observed in geological samples, have also been isolated from biological specimens, including kidney stones. These nanoparticles have certain properties that are consistent with a novel life form, including in vitro self-replication, and contain lipids, DNA and proteins. Thus, it has been hypothesized that nanoparticles may represent a type of infective agent that initiates stone formation in some patients. Despite a large body of suggestive evidence, the true biological nature of these entities has been elusive, and controversy remains as to whether these nano-sized particles are analogous to other recently described unusual and novel microorganisms, or a transmissible, yet inert nanoparticle. Although unique DNA or RNA has yet to be identified, a proteomic biosignature is beginning to emerge that may allow more definitive clinical investigation. The authors stated that there is need for additional research to further elucidate the role, if any, of calcifying nanoparticles in the formation of kidney stones.
Sayer (2011) stated that nephrolithiasis may be the manifestation of rare single gene disorders or part of more common idiopathic renal stone-forming diseases. Molecular genetics has allowed significant progress to be made in the understanding of certain stone-forming conditions. The molecular defect underlying single gene disorders often contributes to a significant metabolic risk factor for stone formation. In contrast, idiopathic renal stone formation relates to the interplay of environmental, dietary and genetic factors, with hypercalciuria being the most commonly found metabolic risk factor. Candidate genes for idiopathic stone formers have been identified using numerous approaches, some of which are outlined here. Despite this, the genetic basis underlying familial hypercalciuria and calcium stone formation remains elusive. The molecular basis of other metabolic risk factors such as hyperuricosuria, hyperoxaluria and hypocitraturia is being unraveled and is allowing new insights into renal stone pathogenesis. The author concluded that the discovery of both rare and common molecular defects leading to renal stones will hopefully increase the understanding of the disease pathogenesis. Such knowledge will allow screening for genetic defects and the use of specific drug therapies in order to prevent renal stone formation.
Tang et al (2012) stated that the role of vitamin D in kidney stone disease is controversial. Current evidence is inconsistent and existing studies were limited by small sample populations. These investigators used the 3rd National Health and Nutrition Examination Survey (NHANES III), a large US population-based cross-sectional study, to determine the independent association between serum 25-hydroxyvitamin D [25(OH)D] concentration and prevalent kidney stone disease in a sample of 16,286 men and women aged 18 years or older. A prevalent kidney stone was defined as self-report of any previous episode of kidney stones. Among 16,286 adult participants, 759 subjects reported a history of previous kidney stones. Concentrations of serum 25(OH)D were not different between stone formers and non-stone formers (mean of 29.28 versus 29.55 ng/ml, p = 0.57). Higher 25(OH)D concentration was not associated with increased odds ratio (OR) for previous kidney stones [OR = 0.99; 95 % confidence interval (CI): 0.99 to 1.01] after adjustment for age, sex, race, history of hypertension, diabetes, body mass index, diuretic use and serum calcium. Furthermore, after these researchers divided 25(OH)D concentrations into quartiles, or into groups using clinically significant cut-offs (e.g., 40 and 50 ng/ml), still no significant differences were found in stone formation in group comparisons. The authors concluded that high serum 25(OH)D concentrations were not associated with prevalent kidney stone disease in NHANES III participants. They stated that prospective studies are needed to clarify the relationship between vitamin D and kidney stone formation, and whether nutritional vitamin D supplementation will increase risk of stone recurrence.
Nguyen et al (2013) noted that increasing 25(OH)D serum levels can prevent a wide range of diseases. There is a concern about increasing kidney stone risk with vitamin D supplementation. These investigators used GrassrootsHealth data to examine the relationship between vitamin D status and kidney stone incidence. The study included 2,012 participants followed prospectively for a median of 19 months; 13 individuals self-reported kidney stones during the study period. Multi-variate logistic regression was applied to assess the association between vitamin D status and kidney stones. These researchers found no statistically significant association between serum 25(OH)D and kidney stones (p = 0.42). Body mass index was significantly associated with kidney stone risk (OR = 3.5; 95 % CI: 1.1 to 11.3). The authors concluded that a serum 25(OH)D level of 20 to 100 ng/ml has no significant association with kidney stone incidence.