Physiopathology of proteinuria and laboratory diagnostic strategy based on single protein analysis

Proteinuria-take a closer look!

Proteinuria is a hallmark of kidney disease. Therefore, measurement of urine protein content plays a central role in any diagnostic work-up for kidney disease. In many cases, proteinuria analysis is restricted to the measurement of total protein content knowing that very high levels of proteinuria (nephrotic proteinuria) are characteristic of glomerular disease. Still, proteinuria can also be a manifestation of impaired tubular protein reabsorption or even be physiological. This review will discuss the physiology of renal protein handling and give guidance on a more sophisticated analysis of proteinuria differentiating albumin, low-molecular weight proteins and immunoglobulins. These non-invasive tests are available in most routine clinical laboratories and may guide the clinician in the diagnostic process before ordering far more expensive (molecular genetic testing) and/or invasive (kidney biopsy) diagnostics.

A clinical study on the difference among proteinuria components in preeclampsia and pregnancies complicated with chronic nephrosis

OBJECTIVE

To explore proteinuria components in preeclampsia (PE) and pregnancies complicated with chronic nephrosis (PCCN).

METHODS

A case-control study was conducted with 81 PE and 95 PCCN patients and 192 normal pregnancies from April 2016 to March 2018. The results of a 24 h proteinuria test and a proteinuria component analysis (PCA) of all enrolled patients were collected. Statistical analyses of variance and SNK-q were conducted to identify the difference between PE and PCCN in urinary protein components using SPSS 23.0 software. A Pearson test and linear regression were conducted to explore the association between 24 h proteinuria and PCA.

RESULTS

Among the PE, PCCN and control groups, the average values of mAlb(2868.5 ± 3119.3 vs 1586.2 ± 3627.0 vs 21.6 ± 23.6), TRF(252.0 ± 280.5 vs 112.9 ± 164.5 vs 3.1 ± 2.7), α1-MG(40.4 ± 40.7 vs 34.0 ± 38.6 vs 10.3 ± 8.0), β2-MG(1.9 ± 5.1 vs 6.8 ± 15.8 vs 0.9 ± 2.3), and RBP(0.9 ± 1.7 vs 3.1 ± 4.5 vs 0.4 ± 0.7) were significantly different (P＜0.001). According to the SNK-q test, the average value of mAlb and TRF in the PCCN group is lower than that in the PE group, but higher than the control group (P < 0.05). The average value of RBP and β2-MG in the PCCN group was higher than the PE and control groups (P < 0.05). The mAlb, TRF, and α1-MG values separately had a significant correlation with the 24 h proteinuria value in PE. The linear regression equation was 24 h proteinuria value = 0.891*mAlb + 5.969*TRF + 1742.378. The mAlb, TRF, α1-MG, β2-MG, and RBP values separately had a significant correlation with the 24 h proteinuria value in PCCN and a linear regression equation of PCCN was as follows: 24 h proteinuria value = 15.148*TRF + 0.571*mAlb.

CONCLUSIONS

The proteinuria components of PE and PCCN patients were different in the elevated β2-MG and RBP. The PCA could be a suitable test for qualitative analysis and an antidiastole for PE and PCCN.

Preanalytical requirements of urinalysis

Urine may be a waste product, but it contains an enormous amount of information. Well-standardized procedures for collection, transport, sample preparation and analysis should become the basis of an effective diagnostic strategy for urinalysis. As reproducibility of urinalysis has been greatly improved due to recent technological progress, preanalytical requirements of urinalysis have gained importance and have become stricter. Since the patients themselves often sample urine specimens, urinalysis is very susceptible to preanalytical issues. Various sampling methods and inappropriate specimen transport can cause important preanalytical errors. The use of preservatives may be helpful for particular analytes. Unfortunately, a universal preservative that allows a complete urinalysis does not (yet) exist. The preanalytical aspects are also of major importance for newer applications (e.g. metabolomics). The present review deals with the current preanalytical problems and requirements for the most common urinary analytes.

Rosuvastatin Increases α-1 Microglobulin Urinary Excretion in Patients With Primary Dyslipidemia

The renoprotective effect of statins has been recently disputed because of observations of proteinuria associated with rosuvastatin treatment, the newest drug of the class. Statin-induced proteinuria findings were mainly based on crudely quantitative dipstick assays. The authors quantitatively evaluated the effect of rosuvastatin at the recommended starting dose of 10 mg/d, on urine protein excretion in patients with primary dyslipidemia. Serum lipid and nonlipid parameters as well as urinary electrolyte, creatinine, and protein (total, albumin, immunoglobulin G, and alpha-1 microglobulin) levels were measured in 40 patients treated with rosuvastatin and 30 controls at baseline and after 12 weeks. The protein-to-creatinine ratios were used to assess urinary protein excretion. Rosuvastatin improved the lipid profile, produced no deterioration of kidney function, but induced a small but significant increase in the excretion of alpha-1 microglobulin (by 16%, P < .05) indicating that statin-related proteinuria involves low-molecular-weight proteins and is of proximal tubular origin.

The value of simultaneous measurements of urinary albumin and total protein in proteinuric patients

BACKGROUND

Proteinuria is a common pathological finding in renal disease. Examining the urinary protein electrophoretic pattern gives clues to the site of origin of the protein. We hypothesized that the type of proteinuria, classified by urine protein electrophoresis and immunofixation (uPEI), may be predicted by simply examining the proportion of higher molecular weight protein (e.g. albumin) in urine total protein content.

METHODS

One thousand and eleven patients, whose urine had been sent to the pathology department for uPEI, were analysed for total protein and albumin to creatinine ratio (uPCR and uACR) and the ratio reported as the albumin to total protein ratio (uAPR). In a group of renal outpatients (n=248), we also specifically measured tubular proteins (N-acetyl-β-D-glucosaminidase, NAG, and β2-microglobulin) and expressed these as ratios to creatinine (uNCR and uβ2CR). To validate these findings, we correlated these measurements with 68 patients in whom we also had renal biopsy data.

RESULTS

In receiver operating characteristic (ROC) curve analysis, the AUC for uAPR was 0.84 for predicting tubular proteinuria pattern on uPEI. In the renal outpatient subgroup, uAPR predicted a tubular pattern of urinary protein equally as well as testing for specific tubular protein markers (uNCR and uβ2CR). In the validation cohort, a uAPR cut-off of <0.40 was 88% sensitive and 99% specific for the diagnosis of primary tubulointerstitial disorders on renal biopsy.

CONCLUSIONS

Useful information about the origins of urinary protein may be inferred by measuring uAPR, the measurement of which is both simple and inexpensive.

The pre-analytical challenges of routine urinalysis

An effective diagnostic strategy for urinalysis should be based on standard procedures for collection, transport, sample preparation and analysis. In view of a better reproducibility of the analyses, the pre-analytical requirements become stricter. Various sample methods can cause significant pre-analytical errors. It is a challenge for the laboratory to control the steps in the pre-analytical phase that contribute to pre-analytical variability. To reduce the variability, it is necessary to look at the pre-analytical process as a complete entity, from test ordering to the moment of specimen processing. Clinical laboratories are responsible for the clinical and financial outcome of this phase. In a culture of increasing productivity, lower costs and improving quality, the challenge is to use several tools designed to standardize and optimize urinalysis. Despite advances in the performance of analytic systems, the pre-analytical phase of modern urinalyses has not been studied very thoroughly. This review of the literature lights on different problems in current pre-analytical requirements for particle and test strip analysis of urine samples.

Tubular toxicity in sirolimus- and cyclosporine-based transplant immunosuppression strategies: an ancillary study from a randomized controlled trial

BACKGROUND

Sirolimus has been promoted as an agent to provide immunosuppression for kidney transplant recipients that, in contrast to calcineurin inhibitors, would not be nephrotoxic. However, several reports have observed proteinuria in patients treated with sirolimus, ranging from low grade to nephrotic range. Accordingly, we compared markers of tubular and glomerular damage in an ancillary study of a randomized trial comparing sirolimus and cyclosporine.

STUDY DESIGN

Single-center, open-label, randomized, prospective trial.

SETTING & PARTICIPANTS

Patients undergoing cadaveric or living donor kidney transplant at the University Hospital in Basel, Switzerland, between January 2001 and July 2004.

INTERVENTION

Immunosuppression regimen consisting of cyclosporine, mycophenolate mofetil, and prednisone versus sirolimus, mycophenolate mofetil, and prednisone.

OUTCOMES

The primary outcome was kidney function, assessed using serum creatinine level. Secondary outcomes included patient and graft survival, number of rejections, and evidence of kidney damage, assessed using glomerular and tubular urine biomarker levels.

MEASUREMENTS

Urine and serum were collected at 0, 7, 30, and 90 days. Kidney function was estimated using serum creatinine level. Urinary markers included alpha(1)-microglobulin and retinol-binding protein (tubular), transferrin and albumin (glomerular), and semiquantitative assessment of glucosuria. Protocol kidney biopsies were performed at days 90 and 180.

RESULTS

There were 63 patients randomly assigned to cyclosporine-based regimens, and 64, to sirolimus-based regimens. Kidney function was similar in both groups, whereas levels of markers associated with glomerular damage (albumin, 19.5 vs 8.96 mg/mmol creatinine; P < 0.001; transferrin, 13.1 vs 5.7 mg/mmol creatinine; P < 0.001) and those associated with tubular damage (alpha(1)-microglobulin, 11 vs 7.6 mg/mmol creatinine; P = 0.004; retinol-binding protein, 19.6 vs 9.6 mg/mmol creatinine; P = 0.002) were higher beginning at day 7 in patients randomly assigned to sirolimus therapy, with similar findings through day 90. Glucosuria incidence was higher in patients randomly assigned to sirolimus therapy beginning by day 30 (65% vs 30% on day 30; P = 0.002; 51% vs 22% on day 90; P < 0.001). On histologic examination, the overall severity of tubular lesions was significantly higher in patients randomly assigned to sirolimus therapy.

LIMITATIONS

Small sample size, short-term follow-up likely insufficient to appreciate calcineurin-associated nephropathy.

CONCLUSION

Compared with a cyclosporine-based immunosuppression regimen, a sirolimus-based regimen is associated with de novo low-grade glomerular proteinuria, increased excretion of markers associated with tubular damage, and evidence of tubular damage on kidney biopsy.

N-acetyl-beta-D-glucosaminidase (NAG) as the most sensitive marker of tubular dysfunction for monitoring residents in non-polluted areas

Alpha(1)-microglobulin (alpha(1)-MG), beta(2)-microglobulin (beta(2)-MG) and N-acetyl-beta-D-glucosaminidase (NAG) are tubular dysfunction markers often used in cadmium (Cd) epidemiology. The purpose of the present study was to identify the best maker among the above-referred three that correlates most closely with Cd in urine of residents with no known Cd pollution. Survey was conducted in 2007-2008 in three prefectures in Japan. Adult women, 2163 in total, participated in the survey; they provided informed consents, offered spot urine samples and filled questionnaires on possible confounders of Cd burden. Urine samples were analyzed for Cd, alpha(1)-MG, beta(2)-MG and NAG together with calcium (Ca), magnesium (Mg), creatinine (CR) and specific gravity (SG). The analyte levels, as observed (e.g., Cd(ob)) or after correction for CR (e.g., Cd(cr)) or SG (e.g., Cd(sg)) were subjected to simple and multiple regression analysis. Correlation matrix analysis with observed values for total cases showed that the coefficients of correlation with Cd were highest for NAG, followed by alpha(1)-MG, and lowest for beta(2)-MG. Multiple regression analysis by three prefectures either separately or in combination (thus four analyses) disclosed that Cd was the independent variable most influential to NAG (as the dependent variable) throughout the four analysis conditions with high R(2) values (>0.3), whereas the most influential variables were not the same depending on the analysis conditions in cases with alpha(1)-MG and beta(2)-MG. When coefficients of correlation for the three dysfunction markers with Cd were compared among the observed, CR- and SG-corrected values, the coefficients for the observed values were higher than the counterpart values for CR- or SG-corrected values. In conclusion, NAG rather than alpha(1)-MG or beta(2)-MG should be recommended for monitoring Cd exposure-related tubular effects among general populations. Observed (i.e., un-corrected) values rather than CR- or SG-corrected values should be used.

Diagnostic potential for urinary proteomics

Urine represents a modified ultrafiltrate of plasma, with protein concentrations typically approximately 1000-fold lower than plasma. Urine’s low protein concentration might suggest it to be a less promising diagnostic specimen than plasma. However, urine can be obtained noninvasively and tests of many urinary proteins are well-established in clinical practice. Proteomic technologies expand opportunities to analyze urinary proteins, identifying more than 1000 proteins and peptides in urine. Urine offers a sampling of most plasma proteins, with increased proportions of low-molecular-weight protein and peptide components. Urine also offers enriched sampling of proteins released along the urinary tract. Although urine presents some challenges as a diagnostic specimen, its diverse range of potential markers offers great potential for diagnosis of both systemic and kidney diseases. Examples of clinical situations where this may be of value are for more sensitive detection of kidney transplant rejection or of renal toxicity of medications.

Analytical performance of the Iris iQ200 automated urine microscopy analyzer

BACKGROUND

We evaluated the Iris iQ200 Automated Urine Microscopy Analyzer to find out if the instrument performed better than traditional visual bright field microscopy in detecting basic urine particles, as assessed against reference phase contrast microscopy.

METHODS

The HUSLAB quality system was followed in planning and completing the evaluation process. The iQ200 instrument results from 167 mid-stream, uncentrifuged urine specimens were compared to those obtained with phase contrast reference microscopy, and to those with routine bright field microscopy. Linearity, carry-over and precision were tested according to well-established protocols.

RESULTS

The iQ200 counted erythrocytes (RBC) at r=0.894 (R(2)=0.799) with Automated Particle Recognition (APR) software alone and at r=0.948 (R(2)=0.898) after re-classification. The performance for leukocytes (WBC) was r=0.885 with APR and r=0.978 after re-classification. The correlations of counting after user re-classification were r=0.927 for squamous epithelial cells (SQEP), r=0.856 for casts, and r=0.706 for non-squamous epithelial cells. The iQ200 showed good linearity and precision and no carry-over was detected.

CONCLUSIONS

The Iris iQ200 was capable to count reliably RBC, WBC, and SQEP cells and to identify a fraction of bacteria and renal elements. Counting results equalled or exceeded that of routine bright field microscopy or earlier flow cytometric technology. The instrument eliminates manual sample preparation but requires a well-trained technologist for re-grouping of findings.

Assessment of renal injury in vivo

The ICH S7A (Safety Pharmacology for Human Pharmaceuticals) guidelines specify that potential adverse pharmacologic effects of a test substance on renal function should be evaluated in supplemental studies when there is a cause for concern (ICH, 2001). For the most part, this can easily be accomplished by examination of the appropriate analytes in urine and blood collected as part of the routine preclinical safety studies. This review will serve as an overview of the selection, interpretation and limitations of standard clinical pathology methods (serum chemistry and urinalysis) for assessment of renal function in such studies, as well as provide some information on emerging biomarkers of renal function.

Urinary protein fraction in healthy subjects using cellulose acetate membrane electrophoresis followed by colloidal silver staining

We previously reported a rapid and highly sensitive colloidal silver staining solution suitable for the cellulose acetate membrane. This method was useful for detecting even very small amounts of urinary protein. In the present study, we examined urinary protein fractions in healthy subjects, using cellulose acetate membrane electrophoresis (CAE) with a highly sensitive colloidal silver staining, in an attempt to determine the clinical relevance of urinary protein fractions. Sixty unconcentrated spot urine specimens were analyzed by CAE and calculated by densitometry. All of the samples were separated into five fractions by CAE. The mean +/- 1 SD of the percentage of five fractions was 28.37 +/- 8.51 in albumin, 4.30 +/- 4.19 in alpha1-globulin, 14.41 +/- 6.14 in alpha2-globulin, 19.45 +/- 7.10 in beta-globulin, and 33.46 +/- 8.24 in gamma-globulin. The albumin/globulin (A/G) ratio was 0.41 +/- 0.17. These six items and the concentrations of total protein, albumin, and beta-N-acetyl-D-glucosaminidase (NAG) did not significantly differ between males and females. NAG is the marker of tubulointerstitial nephropathy. The results suggest that there are no gender-dependent differences in the urinary protein fractions of healthy subjects.

α1-Microglobulin as a promising marker of cadmium-induced tubular dysfunction, possibly better than β2-microglobulin

The purpose of the present study was to evaluate the validity of alpha1-microglobulin (alpha1-MG) in comparison with popularly used beta2-microglobulin (beta2-MG). A database on 8975 cases of never-smoking adult women was revisited; the data were based on spot urine samples from the women in 10 prefectures all over Japan. The validity of alpha1-MG was examined following essentially the same protocol as beta2-MG was examined in a previous study. Comparisons were made for alpha1-MG as observed (e.g. alpha1-MG(ob)), as corrected for creatinine (CR or cr) (e.g. alpha1-MGcr) and as corrected for a specific gravity (SG or sg) of 1.016 (e.g. alpha1-MGsg). A cut-off value of 5.0 mg alpha1-MG/g cr or l was deduced from 400 microg beta2-MG/g cr taking advantage of the regression equation between alpha1-MG and beta2-MG. The prevalence of alph1-microglobulinuria as corrected for a specific gravity of 1.016 (or alpha1-MGsg-uria in short) was essentially unchanged irrespective of SG, except for in very dense or very thin urine samples. alpha1-MGcr-uria prevalence decreased at higher CR. Comparison of the present observation with previous findings on beta2-MG-uria prevalence showed that the variation in prevalence of MG-uria as a function of urine density was smaller for alpha1-MGsg whereas it was substantially larger for beta2-MGcr, and thus it appeared prudent to consider alpha1-MGsg rather than beta2-MGcr as a marker of tubular dysfunction.

Proteinuria: The diagnostic strategy based on urine proteins differentiation

Basal glomerular membrane represents mechanical and electrical barrier for passing of the plasma proteins. Mechanical barrier is composed of cylindrical pores and filtration fissure, and negative layer charge in exterior and interior side of basal glomerular membrane, made of heparan sulphate and sialoglicoproteine, provides certain electrical barrier. Diagnostic strategy based on different serum and urine proteins enables the differentiation of various types of proteinuria. Depending on etiology of proteinuria it can be prerenal, renal and postrenal. By analyzing albumin, armicroglobulin, immunoglobulin G and armacroglobulin, together with total protein in urine, it is possible to detect and differentiate causes of prerenal, renal (glomerular, tubular, glomerulo-tubular) and postrenal proteinuria. The adequate and early differentiation of proteinuria type is of an immense diagnostic and therapeutic importance.

Effects of Acute, Heavy-Resistance Exercise on Urinary Peptide Hormone Excretion in Humans

To examine physical exercise-related changes in urinary excretion of protein/peptide hormones and to correlate modifications with the general increase in post-exercise proteinuria, urine C-peptide, insulin and insulin-like growth factor-I (IGF-I) and their plasma concentrations were measured. Plasma and urinary C-peptide, insulin and IGF-I before (Bex) and at the end (Eex) of physical exercise (a 2.5-hour competition, 102 km) were analysed in 20 young cyclists. At Eex compared with Bex, concentration of urinary C-peptide decreased slightly but significantly (21.3 +/- 2.7 vs. 13.5 +/- 1.7 nmol/l), but urinary insulin and urinary IGF-I concentrations significantly increased at Eex (92.5 +/- 4.2 vs. 131.4 +/- 15.7 pmol/l and 10.0 +/- 2.1 vs. 33.6 +/- 3.8 pmol/l, respectively). Plasma insulin and plasma C-peptide significantly decreased, whereas plasma IGF-I was unchanged. Urinary concentrations of total proteins and creatinine significantly increased. Both Eex urinary C-peptide/urinary protein and urinary C-peptide/urinary creatinine ratios were significantly reduced. The correlation between C-peptide and insulin in plasma was confirmed at Bex as well as Eex, but in urine only at Bex. An increased renal tubular reabsorption of C-peptide at the end of exercise might be suggested, but the expected values considering creatinine excretion were almost three times less. The Eex urinary insulin concentration was higher than expected, considering the circulation levels, but lower when compared with the expected concentration considering creatinine excretion. Physical exercise proteinuria, related to an increased protein filtration and a saturation of the mechanisms responsible for the reabsorption, does not appear similar for all peptide hormones.

Classification of renal proteinuria: a simple algorithm

Total protein, albumin, alpha1-microglobulin, and immunoglobulin G (IgG) were analyzed in 1,622 urine samples without Bence-Jones proteinuria or gross hematuria. There was correlation with the histological picture obtained on renal biopsy in 61 patients. We established 24-h reference intervals for alpha1-microglobulin and IgG on 659 urine samples with total protein and albumin excretion rates below 100 mg/24 h and 30 mg/24 h, respectively, and creatinine clearance above 80 ml/min. The central 95% reference interval was found to be between 4 and 17 mg/24 h for alpha1-microglobulin and between 3 and 8.5 mg/24 h for IgG. In 80 urine samples with albumin excretion rate above 30 mg/24 h and alpha1-microglobulin and IgG within their reference intervals, we analyzed the 95% central interval of the distribution of the IgG/albumin ratios, and it was found to be within 0.01 and 0.20 (0.90 confidence interval: 0.17-0.24). Proteinuria was considered to be of the selective glomerular type if the albumin excretion rate was abnormal and the IgG/albumin ratio was under 0.20, even when the IgG excretion was within a pathological range. For the classification of proteinuria as predominantly tubular, we estimated the alpha1-microglobulin/albumin ratio in 173 urine samples with normal excretion rates of albumin and IgG and pathological excretion of alpha1-microglobulin. The discriminating value of 0.91 (0.90 confidence interval: 0.78-1.08) was accepted in order to define proteinuria of a tubular origin in the presence of a pathological albumin excretion rate. The association between albumin and IgG excretion rates and tubular reabsorption of the alpha1-microglobulin normally filtered by the glomerulus was studied in 33 urine samples from patients with no histologically significant tubulo-interstitial or vascular disease and a serum creatinine concentration below 141 pmol/l. The optimal curve-fitting function between albumin plus IgG and alpha1-microglobulin excretion rates was of the quadratic type (r = 0.927). Mixed proteinuria was considered when both, albumin and alpha1-microglobulin excretion rates were pathological and could not be included in the previously described groups.

Oxypurines, protein, glucose and the functional state of blood vasculature are markers of renal calcium stone-forming processes? Observations in men with idiopathic recurrent calcium urolithiasis

In idiopathic calcium urolithiasis the relationships between oxypurines, accompanying proteins and glucose in urine and plasma, and the associated metabolic activity (MA) are unknown. To establish whether MA is related to these parameters and to calcium oxalate crystallization, or whether it reflects a reaction of metabolism to systemic insults was the major goal of the work. One hundred fifty one males were studied in three trials: trial 1 (n=130 patients) and trial 2 (n=24 patients) were cross-sectional; trial 3 included 11 patients and 14 controls). Mean age was 46 years (trials 1 and 2) and 29 years (trial 3). In trial 1 the stratification was based on the median urinary oxypurine excretion, in trial 2 on the median plasma oxypurine concentration (below or above: Low and High subgroups). No dietary restrictions were imposed, but standardized ambulatory laboratory testing was carried out. MA was quantitated by a score. Established analytical methods were used, except for oxypurine measurement which was done by high performance liquid chromatography. Patients with kidney stones tended to be overweight (body mass index >25 kg/(m)2) and to have fasting hyperglycemia. In trial 1 severe oxypurinuria, and especially severe xanthinuria, was associated with an increase in urinary pH, creatinine clearance, proteins, uric acid, malonedialdehyde (indicator of lipid peroxidation), systolic blood pressure, and with a decrease in plasma uric acid (synonymous with a decrease of antioxidant capacity). Tubular reabsorption of proteins and stone-forming substances was diminished but MA remained unchanged despite slightly increased calcium oxalate crystal growth. In trial 2 high adenosine and xanthine coincided with elevated systolic and diastolic blood pressure, high uric acid with high urinary malonedialdehyde, high summed oxypurines minus uric acid with an increase of diastolic blood pressure, glycemia and MA; urinary nitrate (indicator of systemic vasodilation) was unchanged. In trial 3 patients' oxypurinemia and proteinuria were normal, but body mass index, glycemia and insulinemia were increased. Urinary total protein, albumin and non-albumin proteins were positively predicted (multivariate regression analysis) by urinary xanthine, glucose and pH (trial 1); MA was positively (trial 3) or negatively (trial 2) predicted by urinary total protein. In calcium urolithiasis, a disorder of affluence, 1) oxypurinuria and proteinuria and oxypurinemia and MA appear causally linked, presumably via oxidant/antioxidant imbalance-induced renal tissue damage; 2) urinary proteins may act as inhibitors or promoters of stone-forming processes; 3) a stone-initiating role of impaired vasodilatation is conjectural; 4) overweight, obesity, mild glucosuria and hyperdynamic blood circulation are regular signs.

The use of knowledge-based systems to improve medical knowledge about urine analysis

Urine protein diagnostics has developed into a routine method for screening and monitoring kidney diseases. It is based on the quantitative measurement of total protein, albumin, alpha(1)-microglobulin, immunoglobulin G and alpha(2)-macroglobulin (all related to urine creatinine), as well as a dipstick screening. The excretion pattern of the marker proteins allows differentiation of haematuria, leukocyturia and proteinuria and to assign them to prerenal, renal and postrenal causes. In order to provide the clinical partner not only with pure analytical results, but to support clinical decision making by an interpretative report, a urine protein expert system (UPES) has been developed. Based on a database containing more than 500 excretion patterns of patients with known diagnoses, a knowledge base was extracted. In its modules plausibility control, glomerular filtration rate, hematuria, leukocyturia and proteinuria, IF-THEN-rules interpret the given patterns and select matching text elements. The knowledge base has been integrated in the modern expert system shell WILAS, and the resulting interpretation system has been thoroughly verified and validated. An internal acceptance study revealed that urine protein differentiation is widely accepted as a diagnostic option and that its interpretation, provided with the help of UPES, is appreciated as a service. In an external study, the usability of UPES in routine and its knowledge representation was evaluated in 11 centres consisting of laboratories and nephrological partners. Over seven months, more than 500 cases were interpreted using UPES and documented by questionnaires. The discussion of the results at a user conference revealed that the problem of analytical standardisation as well as the common definition of diagnostic terms by laboratory staff and clinicians play a crucial role for the use of knowledge-based systems in laboratory medicine. Whereas the user interface of UPES was judged very heterogeneously, the correctness of the proposed interpretations was unanimously rated as "good". As a result of the evaluation, the user interface has been modernised. The knowledge base has been extended to address paediatric issues as well, and to take clinical information and previous findings into consideration.

Early diagnosis of endemic nephropathy

Urinary alpha(1)-microglobulin as a tubular marker and albumin as a glomerular marker were measured in 373 subjects living in a typical endemic village of Kaniza, Croatia, previously classified as diseased, suspect, 'at risk' and others according to the criteria used for the diagnosis of endemic nephropathy. Based on the excretion pattern of alpha(1)-microglobulin and albumin and its extent, significant tubular with significant glomerular proteinuria was found in seven diseased subjects. Significant tubular proteinuria with slight glomerular proteinuria was found in one diseased subject, while another diseased subject had slight tubular with significant glomerular proteinuria. Significant tubular with significant glomerular proteinuria was found in only one suspect subject. Also, significant tubular proteinuria was established in one other subject.

Urinalysis to exclude and monitor nephrotoxicity

A large number of compounds, which are in common usage in industry and medicine, are potentially nephrotoxic. Renal damage and disease resulting from toxic exposure is progressive and will, if unarrested, culminate in irreversible renal disease. There is, therefore, a need to develop a battery of tests with which to monitor and characterise the nephrotoxic cascade. A European-wide study compared biomarker profiles of adult male workers who were exposed to heavy metals or solvents. It became apparent that the urinary profiles varied with the nature of the toxin, reflecting the functional region of the kidney affected and also the severity of the damage. Children are a particularly vulnerable group and the investigation of range of biomarkers indicated that they were indeed susceptible to nephrotoxic pollutants in their environment. It is proposed that a small cohort of tests should be used to monitor the early (pre-clinical stages) of renal damage or dysfunction; these can be supplemented if necessary by additional specific tests. In the future better information on at-risk populations and genetic information will enable the determination of individual susceptibility to be assessed more precisely.

A review on urinary proteins in outflow disease of the upper urinary tract

INTRODUCTION

[corrected] No review articles on outflow disease of the upper urinary tract discuss urinary protein excretion.

DISCUSSION

Following acute partial and/or complete ureteral obstruction (UO) or chronic partial UO, alpha-1-microglobulin excretion is significantly higher than in the reference population or patients with proven renal dilatation without obstruction, but is not found to be diagnostic for these conditions as such. Chronic partial UO is followed first by a destructive and then by a steady-state phase in renal damage. The observed increase in tubular proteinuria during the destructive phase correlates with the decrease in absolute dimercaptosuccinic acid (DMSA) uptake. If the destructive phase is not followed by a stable phase, a mixed tubular and glomerular proteinuria is seen. Urinary alpha-1-microglobulin excretion is found to be diagnostically useful in vesico-ureteral reflux (VUR) patients, increases with higher intravesical-intrapyelic pressure, correlates with the decrease in absolute DMSA uptake or with urinary epidermal growth factor excretion (both markers of the number of functioning nephrons) and predicts the outcome after treatment.

CONCLUSION

alpha-1-Microglobulin is useful in the detection of renal tubular damage in patients with outflow disease of the upper tract, is diagnostic for VUR but is not so for ureteral obstruction.