The surgeon's role on chemical investigations of the composition of urinary stones.

The chemical analysis of an urolith is often interpreted as "stone's composition". However, it must be taken into consideration, that in most cases, only a fragment of the stone has been sent to the laboratory. In some recurrent patients, stone compositions either vary considerably between episodes or the analytical result obtained from the stone fragment does not fit with the data of e.

Kinetics of calcium oxalate crystal formation in urine.

It is routinely observed that persons with increased urinary stone risk factors do not necessarily form uroliths. Furthermore, stone formers can present with urinalyses that do not reflect the clinical picture. We explain this discrepancy by differences in crystallization kinetics.

Hydrophobic forces as a key factor in crystalline biofilm formation on ureteral stents.

Background: Current discussions about biofilm formation focus on the solid/liquid interface between a medical device and body fluids. Yet it has been shown that gas bubbles (GB) can stably form on ureteral stents in artificial urine and that their fate depends on the stent's surface properties. The liquid/gas interface constitutes an adhesion site for precipitating salts as well as hydrophobic organic molecules.

Ureteral stents should be soaked for several minutes before placement.

Purpose: Placement of ureteral stents (DJ-stents) may lead to complications. Inappropriate friction properties of the implant are, inter alia, made responsible for primary injuries, injury-related inflammation and a cascade of consecutive side effects. Hydrophilicity is considered to be related to low friction.

Urolithiasis--an interdisciplinary diagnostic, therapeutic and secondary preventive challenge.

Background: The prevalence of urolithiasis in Germany is 4.7%; its incidence has trebled in the last three decades. The risk of recurrence is 50-80%, depending on the type of stone, unless secondary prevention is instituted.

Induced urinary crystal formation as an analytical strategy for the prediction and monitoring of urolithiasis and other metabolism-related disorders.

Crystal formation reflects the entire composition of the surrounding solution. In case of urolithiasis, induced crystal formation in native urine has led to the development of the Bonn-Risk-Index (BRI), a valuable tool to quantify an individual's risk of calcium oxalate urolithiasis. If the progression of a disease is associated with characteristic changes in the activities of urinary components, this leads to an altered urinary crystallisation capacity.

Correspondence between Ca²⁺ and calciuria, citrate level and pH of urine in pediatric urolithiasis.

Background: Hypercalciuria and hypocitraturia are considered the most important risk factors for urolithiasis. Citrate binds to urinary calcium to form a soluble complex which decreases the availability of ionized calcium (Ca(2+)) necessary for calcium oxalate formation and phosphate crystallization. The aims of this study were to assess the Ca(2+) fraction in relation to total calciuria, citraturia and urinary pH and to determine whether urinary Ca(2+) concentration is a helpful biomarker in metabolic evaluation of children with urolithiasis.

Assessment of lithogenic risk in children based on a morning spot urine sample.

Purpose: The Bonn Risk Index has been used to evaluate the risk of urinary calcium oxalate stone formation. According to the original method, risk should be determined based on 24-hour urine collection. We studied whether the Bonn Risk Index could be measured in spot urine samples and which part of the day is most suitable for this purpose.

Metabolic stress response patterns in urinary compositions of idiopathic calcium oxalate stone formers, patients with chronic bowel diseases and controls.

Emotional stress is associated with e.g. increased hormone release, high blood-sugar level and blood pressure.

Analytical precision of the Urolizer for the determination of the BONN-Risk-Index (BRI) for calcium oxalate urolithiasis and evaluation of the influence of 24-h urine storage at moderate temperatures on BRI.

Background: Since its first publication in 2000, the BONN-Risk-Index (BRI) has been successfully used to determine the calcium oxalate (CaOx) crystallization risk from urine samples. To date, a BRI-measuring device, the "Urolizer", has been developed, operating automatically and requiring only a minimum of preparation. Two major objectives were pursued: determination of Urolizer precision, and determination of the influence of 24-h urine storage at moderate temperatures on BRI.

Relevance of the BONN Risk Index for metabolic monitoring of patients with calcium oxalate urolithiasis: a clinical application study of the Urolizer.

The BONN Risk Index (BRI) successfully determines the calcium oxalate (CaOx) crystallization risk from urine samples. The BRI is based on a standardized crystallization test performed on native urine. A BRI-measuring device, the "Urolizer", has been developed, operating automatically and requiring only a minimum of preparative efforts.

Calcium oxalate stone formation risk - a case of disturbed relative concentrations of urinary components.

Background: Although afflicted with stone formation, urolithiasis patients often present with normal renal excretions of lithogenic and inhibitory substances. In this study, crystal formation is not interpreted as the result of urinary excretions simply exceeding the static limits of normal ranges but rather as the consequence of relative combinations of such parameters which convert urine into becoming potentially lithogenic. Our model embraces different triplet combinations of fundamental urinary risk factors for calcium oxalate (CaOx) crystallization, to characterize different levels of urinary stone formation risk.

The distribution of crystalline material in obstructed stents--in need for intra-luminal surface modification?

Purpose: Usually, hampered urine flow and failing of Seldinger technique leads to the explanation "obstructed ureteral stent" with no further clarification where exactly the obstructions are located. If stent obstruction is caused by intra-luminal biofilm and/or crystal deposits, the need of biofilm reducing coatings on the stent's inside has to be discussed.

Materials And Methods: We investigated 59 stents from patients in whom acute hydronephrosis and/or acute pyelonephritis required stent replacement and/or usage of Seldinger technique failed.

Hyperoxaluria, hypocitraturia, hypomagnesiuria, and lack of intestinal colonization by Oxalobacter formigenes in a cervical spinal cord injury patient with suprapubic cystostomy, short bowel, and nephrolithiasis.

Although urolithiasis is common in spinal cord injury patients, it is presumed that the predisposing factors for urinary stones in spinal cord injury patients are immobilization-induced hypercalciuria in the initial period after spinal injury and, in later stages, urine infection by urease-producing micro-organisms, e.g., Proteus sp.

Diamond-like carbon coatings on ureteral stents--a new strategy for decreasing the formation of crystalline bacterial biofilms?

Purpose: Any catheter material placed in the urinary tract provides a surface for bacterial colonization and, therefore, it is susceptible to encrustation with crystalline bacterial biofilm. Encrustation and blockage by biofilms remain a major complication in patient care. Most patients with indwelling ureteral stents experience irritative symptoms related to these implants and many experience discomfort.

Computation and modeling of the stone-growth related urinary depletion effect using "depletion V1.0".

Purpose: During metabolic evaluation stone patients often present with calculi in the urinary tract or are suffering from high frequent formation of small microliths passing routinely the urinary tract. These concrements are presumably in a state of continuous growth. Consequently, the concentrations of the lithogenic components in the voided urine must decrease.

Why does the Bonn Risk Index discriminate between calcium oxalate stone formers and healthy controls?

Purpose: The BRI has been shown to discriminate between calcium oxalate stone formers and controls. BRI is the ratio of the concentration of ionized calcium and the amount of oxalate that must be added to 200 ml urine to initiate crystallization. Higher BRI values are predictive of being a stone former and a value of 1.

The use of risk indices: do they predict recurrence? Yes, they (at least some) do.

A suitable and advisedly used risk index is an effective tool for improving prevention, therapy monitoring and classification of almost unmanageable amounts of analysis data and diagnoses. In contrast to statistically founded indices, causality-based risk indices can provide a fundamental insight into the mechanisms of the underlying pathology. However, understanding of stone formation as the result of many linked and often non-linear individual processes must be further improved.

Oxalate degrading bacteria: new treatment option for patients with primary and secondary hyperoxaluria?

Current treatment options in patients with primary and secondary hyperoxaluria are limited and do not always lead to sufficient reduction in urinary oxalate excretion. Intestinal oxalate degrading bacteria are capable of degrading oxalate to CO(2) and formate, the latter being further metabolized and excreted via the feces. It is speculated, that both endogenously produced, as well as dietary oxalate can be significantly removed via the intestinal tract.

Oxalate and its handling in a low stone risk vs a stone-prone population group.

Despite hyperoxalurogenic eating habits relative to white subjects, South African blacks have urinary oxalate excretions, Tiselius risk indices (AP(CaOx)) and calcium oxalate saturations, which do not differ significantly from those of their white counterparts. The present study was undertaken to establish whether the BONN-Risk-Index (BRI) might discriminate between the urines of the two population groups and whether differences might exist in their respective gastrointestinal absorption rates of oxalate. Participants (n = 15 in each group) provided 24 h urines on their free diets for BRI determination.

Absorptive hyperoxaluria leads to an increased risk for urolithiasis or nephrocalcinosis in cystic fibrosis.

Background: Hyperoxaluria has been incriminated to account for the increased incidence of urolithiasis or nephrocalcinosis in patients with cystic fibrosis (CF). Hyperoxaluria presumably is caused by fat malabsorption and the absence of such intestinal oxalate-degrading bacteria as Oxalobacter formigenes. To better elucidate its pathophysiological characteristics, we prospectively studied patients with CF by determining these parameters and performing renal ultrasonography twice yearly.

Can the Bonn Risk Index be replaced by a simple measurement of the urinary concentration of free calcium ions?

Purpose: It has been shown that a strong hyperbolic relationship exists between the urinary concentration of free Ca ions ([Ca]) and the amount of ammonium oxalate (Ox) that must be titrated in a standardized procedure to a urine sample to induce CaOx crystallization. The ratio of [Ca] to (Ox) is termed the Bonn Risk Index (BRI). Most data plot around a hyperbola described by the formula, [Ca] x (Ox) = constant.

Hypocitraturia as a risk factor for nephrocalcinosis after kidney transplantation.

Calcium-oxalate crystal deposition in kidney transplant biopsy specimen led us to investigate the impact of calcineurin inhibitor treatment on urinary excretion of lithogenic and stone inhibitory substances in 53 children after successful kidney transplantation (KTx) receiving cyclosporine A (CsA) or tacrolimus. We compared the values obtained with those of 12 patients with recurrent nephrotic syndrome under CsA and of 6 patients with Rasmussen encephalitis (RE) under tacrolimus therapy. Renal ultrasound examinations were repeatedly performed.