Differentiation of proteinuria and haematuria by single protein analysis in urine

Urine transfer devices may impact urinary particle results: a pre-analytical study

OBJECTIVES

Well-standardized procedures in the pre-analytical phase of urine diagnostics is of utmost importance to obtain reliable results. We investigated the effect of different urine collection methods and the associated urine transfer tubes on urine test strip and particle results.

METHODS

In total, 146 selected urine samples were subdivided into three different collection containers and subsequently transferred into its accompanying transfer tube (BD, Greiner, Sarstedt vacuum and Sarstedt aspiration). As reference, the original urine sample was directly measured on the analyser. Both chemical test strip analysis (Sysmex UC-3500) and fluorescence flow cytometry particle analysis (Sysmex UF-5000) were performed on all samples.

RESULTS

No statistically significant differences in test strip results were found between the studied transfer methods. On the contrary, transfer of urine samples to the secondary tubes affected their particle counts. Clinically significant reductions in counts of renal tubular epithelial cells and hyaline casts were observed using the BD and Greiner transfer tubes and in counts of pathological casts using the BD, Greiner and Sarstedt vacuum tubes.

CONCLUSIONS

The results of this study indicate that the use of urine transfer tubes may impact counts of fragile urine particles. Clinical laboratories need to be aware about the variation that urine collection methods can induce on urine particle counts.

Albuminuria Is Affected by Urinary Tract Infection: A Comparison between Biochemical Quantitative Method and Automatic Urine Chemistry Analyzer UC-3500

The automated urine reagent strip test is a cost-effective tool for detecting albuminuria in patients. However, prior research has not investigated how urinary tract infections (UTIs) affect the test's accuracy. Therefore, this study aims to assess the impact of UTIs on albuminuria diagnosis using both the biochemical quantitative method and the test strip method of the Fully Automatic Urine Chemistry Analyzer, UC-3500 (Sysmex, Kobe, Japan). From March to December 2019, we prospectively collected midstream urine from adult female UTI patients before and after one week of cephalexin treatment. The urine samples were subjected to culture, routine urinalysis, and albuminuria diagnosis using the biochemical quantitative method and UC-3500. Albuminuria was defined as a urine albumin to creatinine ratio (UACR) ≥ 30 mg/g in the biochemical quantitative method. The results were compared between the two methods. Among fifty-four female patients (average age: 50.5 ± 4.4 years) with UTIs, 24 (44.44%) had transient albuminuria. The quantitative UACR significantly decreased after one week of antibiotic treatment (median: 53 mg/g to 9 mg/g; median difference: -0.54, p < 0.0001). UC-3500 exhibited a higher false positive rate for diagnosing albuminuria during UTIs (42%) compared to after treatment (19%). Its agreement with the biochemical quantitative method was moderate during UTI (κ = 0.49, 95% confidence interval [CI]: 0.24-0.73) and good after treatment (κ = 0.65, 95% CI: 0.45-0.86). UC-3500's accuracy in diagnosing albuminuria is influenced by UTIs, leading to either transient albuminuria or a false positive reaction of the test strip. UTI should be excluded or treated before its application in albuminuria screening.

Proteinuria in Dent disease: a review of the literature

BACKGROUND

Dent disease is a rare X-linked recessive proximal tubulopathy caused by mutations in CLCN5 (Dent-1) or OCRL (Dent-2). As a rule, total protein excretion (TPE) is low in tubular proteinuria compared with glomerular disease. Several authors have reported nephrotic-range proteinuria (NP) and glomerulosclerosis in Dent disease. Therefore, we aimed to analyze protein excretion in patients with documented CLCN5 or OCRL mutations in a systematic literature review.

DESIGN

PubMed and Embase were searched for cases with documented CLCN5 or OCRL mutations and (semi-)quantitative data on protein excretion. The most reliable data (i.e., TPE > protein-creatinine ratio > Albustix) was used for NP classification.

RESULTS

Data were available on 148 patients from 47 reports: 126 had a CLCN5 and 22 an OCRLmutation. TPE was not significantly different between both forms (p = 0.11). Fifty-five of 126 (43.7 %) Dent-1 vs 13/22 (59.1 %) Dent-2 patients met the definition of NP (p = 0.25). Serum albumin was normal in all reported cases (24/148). Glomerulosclerosis was noted in 20/32 kidney biopsies and was strongly related to tubulointerstitial fibrosis, but not to kidney function or proteinuria.

CONCLUSION

More than half of the patients with both forms of Dent disease have NP, and the presence of low molecular weight proteinuria in a patient with NP in the absence of edema and hypoalbuminemia should prompt genetic testing. Even with normal renal function, glomerulosclerosis and tubulointerstitial fibrosis are present in Dent disease. The role of proteinuria in the course of the disease needs to be examined further in longitudinal studies.

α1-Microglobulin/albumin ratio may improve interpretation of albuminuria in statin-treated patients

BACKGROUND

Statins can cause tubular proteinuria by inhibiting tubular reabsorption of urinary proteins. To distinguish between microalbuminuria originating from glomerular leakage of albumin and tubular microalbuminuria due to statin therapy, the α1-microglobulin/albumin ratio is evaluated in patients taking statins and compared to untreated patients.

METHODS

Ten apparently healthy subjects were given 40 mg of simvastatin and tested for urinary α1-microglobulin, albumin, creatinine and cystatin C, up to 24 h after administration. Additionally, urine samples of 76 statin-treated and 456 untreated patients presenting with micro-albuminuria (albuminuria range between 20 and 200 mg/L) were tested for α1-microglobulin and albumin. α1-Microglobulin/albumin ratios were compared. Total cholesterol was measured in 50 patients on statin therapy.

RESULTS

In the 10 apparently healthy subjects, a significant temporary increase of α1-microglobulin, albumin and α1-microglobulin/albumin ratio was observed after statin intake. In the group of 532 patients showing micro-albuminuria, those treated with statins showed a significantly higher mean urinary α1-microglobulin/albumin ratio then untreated patients. Urinary albumin concentrations were significantly higher in patients taking simvastatin than in patients on rosuvastatin treatment and they were also higher in patients on statin therapy with a total serum cholesterol concentration below 3.88 mmol/L than in patients with a total serum cholesterol concentration above 5.17 mmol/L.

CONCLUSIONS

Tubular proteinuria, caused by the use of statins, can be distinguished from glomerular proteinuria by a higher urinary α1-microglobulin/albumin ratio.

Evaluation of proteinuria and GFR to diagnose and classify kidney disease: systematic review and proof of concept

Chronic kidney disease is often not associated with significant symptoms or abnormalities in common laboratory test results. Diagnosis is supposedly facilitated by calculating the glomerular filtration rate (GFR) from serum creatinine. A reference range GFR, however, does not exclude renal disease, because renal disease causes the subsequent decrease of renal function. Thorough analysis of proteinuria, however, requires a profound knowledge of the renal handling of the different marker proteins of glomerular and tubular origin. This paper summarizes the scientific basis, explains the diagnostic rationale and proves the concept by analyzing 5669 samples, where GFR and proteinuria work-up were available. 63% (1446 of 2287) of the samples with a GFR above 60 showed either glomerular (37.8%, n=865) or tubular proteinuria (25.4%, n= 581). The quantity of proteinuria increased severely with decreasing kidney function. The rate of glomerular proteinuria remained nearly constant in the different GFR groups, while primarily tubular proteinuria increased from 23% to 63%. A proteinuria pattern indicating a good response to therapy was frequently combined with a high GFR (selective glomerular proteinuria/ incomplete tubular proteinuria), while the severe forms of unselective or complete tubular proteinuria associated with a severe GFR decrease. Regression analysis showed a better inverse correlation of GFR with tubular (r=-0.643) than glomerular markers (r=-0.360; combined r=-0.646). We believe that this complex interrelated laboratory information must be delivered most effectively, i.e. with the use of a knowledge based system in combination with improved, visual oriented laboratory output.

Alpha 1-microglobulin: clinical laboratory aspects and applications

BACKGROUND

Urinary microproteins are becoming increasingly important in clinical diagnostics. They can contribute in the non-invasive early detection of renal abnormalities and the differentiation of various nephrological and urological pathologies. Alpha 1-microglobulin (A1M) is an immunomodulatory protein with a broad spectrum of possible clinical applications and seems a promising marker for evaluation of tubular function.

METHOD

We performed a systematic review of the peer-reviewed literature (until end of November 2003) on A1M with emphasis on clinical diagnostic utility and laboratory aspects.

CONCLUSIONS

A1M is a 27-kDa glycoprotein, present in various body fluids, with unknown exact biological function. The protein acts as a mediator of bacterial adhesion to polymer surfaces and is involved in inhibiting renal lithogenesis. Because A1M is not an acute phase protein, is stable in a broad range of physiological conditions and sensitive immunoassays have been developed, its measurement can be used for clinical purposes. Unfortunately, international standardisation is still lacking. Altered plasma/serum levels are usually due to impaired liver or kidney functions but are also observed in clinical conditions such as HIV and mood disorders. Urinary A1M provides a non-invasive, inexpensive diagnostic alternative for the diagnosis and monitoring of urinary tract disorders (early detection of tubular disorders such as heavy metal intoxications, diabetic nephropathy, urinary outflow disorders and pyelonephritis).

Ureteroscopy for benign hematuria

Any patient presenting with hematuria of unknown origin should undergo a thorough history, physical examination, and laboratory and radiographic work-up. All attempts should be made to exclude malignancy. Renal hemangiomas are the most likely cause of chronic benign hematuria, particularly in young patients. In the past these lesions were treated with complete or partial nephrectomy. With the availability of small, flexible ureteroscopes capable of primary and secondary deflection, ureterorenoscopy has become an excellent means of diagnosing and treating these lesions. Various instruments--including an electrocautery probe, Nd:YAG laser, and Holmium:YAG laser--have been used with similar results.

Molecular cloning and characterization of a novel carboxylesterase-like protein that is physiologically present at high concentrations in the urine of domestic cats (Felis catus)

Normal mammals generally excrete only small amounts of protein in the urine, thus avoiding major leakage of proteins from the body. Proteinuria is the most commonly recognized abnormality in renal disease. However, healthy domestic cats ( Felis catus ) excrete proteins at high concentrations (about 0.5 mg/ml) in their urine. We investigated the possible cause of proteinuria in healthy cats, and discovered a 70 kDa glycoprotein, which was excreted as a major urinary protein in cat urine, irrespective of gender. To elucidate the biochemical functions and the excretion mechanism of this protein, we cloned the cDNA for this protein from a cat kidney cDNA library. The deduced amino acid sequence shared 47% identity with the rat liver carboxylesterase (EC 3.1.1.1), and both the serine hydrolase active site and the carboxylesterase-specific sequence were conserved. Therefore we named this protein cauxin (carboxylesterase-like urinary excreted protein). In contrast to the mammalian carboxylesterases, most of which are localized within the cells of various organs, cauxin was expressed specifically in the epithelial cells of the distal tubules, and was secreted efficiently into the urine, probably because it lacked the endoplasmic reticulum retention sequence (HDEL). Based on our finding that cauxin is not expressed in the immature cat kidney, we conclude that cauxin is involved in physiological functions that are specific for mature cats. Recently, cauxin-like cDNAs were found from human brain and teratocarcinoma cells. These data suggest that cauxin and cauxin-like human proteins are categorized as a novel group of carboxylesterase multigene family.

Windows to the ward: graphically oriented report forms. Presentation of complex, interrelated laboratory data for electrophoresis/immunofixation, cerebrospinal fluid, and urinary protein profiles

BACKGROUND

Automated laboratory analyzers that mass produce data have been linked to information systems for more than two decades, but little progress has been made in developing more comprehensible report forms. Results are still reported in computer-generated printouts containing hundreds of numbers crowded into columns on each printed page.

METHODS

We developed three software applications focusing on the graphic presentation of laboratory results.

RESULTS

The first application summarizes data for a patient with a monoclonal gammopathy. The report provides a cumulative graphic presentation of immunofixation/electrophoresis data without any additional interpretation, focuses on a color-coded electrophoresis scan, and records up to 5 years on a single page. The second application deals with cerebrospinal fluid analysis. The report calculates relevant data and graphs the complex relationship between albumin and immunoglobulin results from paired serum and cerebrospinal fluid samples. Manually added interpretive text assures an output comprehensible to clinicians in all specialties. The third application produces a report summarizing quantitatively measured urinary marker protein profiles. The report form is generated by a flexible, completely user-definable knowledge-based system. It calculates numerous ratios and formulae, supports reflex testing, supplies an automated interpretation, and generates a specific graphic signature pattern of the results (MDI LabLink proteinuria differentiation).

CONCLUSIONS

Increased clinical demand for graphically oriented report forms 5 years after their introduction has provided evidence that these reports transfer complex laboratory data and results to the clinician more effectively. The highest (more than threefold) increase in demand has been for reports for urinary marker protein profiles that feature a largely self-explanatory graphic signature pattern.

Urinary plasma protein patterns in acute prostatitis

We evaluated the diagnostic utility of urinary alpha1-microglobulin, alpha2-macroglobulin and albumin in the diagnosis of acute prostatitis. We studied 133 men (43 +/- 17 years) with, and a reference population (n=36, 41 +/- 16 years) without, urinary tract infection. Prostatectomy samples were used to study the potential interference between prostatic proteins and protein analysis. Urinary alpha2-macroglobulin/albumin ratio was significantly lower in prostatitis compared to the reference population, cystitis or acute pyelonephritis (p < 0.0001). Low alpha2-macroglobulin concentrations in prostatitis are due to inhibition (p = 0.0001) of the immune reaction between alpha2-macroglobulin in presence of polyclonal rabbit antibodies (used for immunonephelometry) by soluble prostatic proteins (+/- 60 kDa) which appear in urine in acute prostatitis. The urinary alpha1-microglobulin/creatinine ratio diagnoses acute pyelonephritis (sensitivity 100% and specificity 87%) and the urinary alpha2-macroglobulin/albumin ratio diagnoses acute prostatitis (sensitivity 100% and specificity of 90%). Stepwise multinomial logistic regression analysis reveals that urinary alpha1-microglobulin, alpha2-macroglobulin, albumin and creatinine provide optimal differentiation between acute pyelonephritis and acute prostatitis (pseudo R2=0.83; Loglikelihood -30.55, p < 0.000001). In conclusion, the combination of hematuria and absence of urinary alpha-2-macroglobulin is diagnostic for acute prostatitis. Even without hematuria, alpha2-macroglobulin remains lower compared to patients without prostatitis.

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.

Interpreting complex urinary patterns with MDI LABLINK: a statistical evaluation

The measurement of urinary marker proteins is not a generally accepted laboratory practice because the results are difficult to interpret. MDI-LABLINK is software for classifying patterns of specific urinary marker proteins. The interpretations are completely user definable thanks to a specific 'pattern definition database'. Our interpretation set is based on Hofmann and Guder's work in measuring and interpreting single urinary proteins. We include additional marker proteins in order to adapt Boesken's SDS-PAGE classification. During the last 3 years, 1905 patterns were fully differentiated and identically interpreted. Firstly, the samples were classified into three patterns: normal (25.8%), predominantly glomerular (27.2%, selective, unselective, mixed, and with additional tubular proteins) and predominantly tubular (36.9%, complete/incomplete form, with additional glomerular proteins); 8.9% showed postrenal proteinuria. Secondly, glomerular selectivity measured by using urinary transferrin/IgG ratio alone correlates well with the established SI index (the ratio between IgG and transferrin clearances). Thirdly, the creatinine concentration substantiates the validity of the sample. The quality of the preanalytical phase can be improved through the ongoing education of the medical staff. Finally, measurement of urinary albumin and alpha-1-microglobulin is mandatory where kidney disease is suspected, has to be ruled out, or requires close monitoring, even when the total protein concentration is normal.

Screening school children for albuminuria, proteinuria and occult blood with dipsticks

Beginning in 1974, the Japanese Ministry of Health Welfare directed the screening of schoolchildren for proteinuria. We studied their procedure and methods in 6197 school children and also evaluated a new urine dipstick that measures albumin concentrations down to about 10 mg/l and creatinine down to about 300 mg/l. We used specimens from adult in- and outpatients to test the accuracy of the dipsticks. Based on the quantitative results, we set as cutoffs < 150 mg/l for protein and < 30 mg/l for albumin as the concentrations representing "low risk." The quantitative values were assumed to be correct, and the dipstick results were judged accordingly, i.e., a dipstick protein of > or = "150" mg/l or an albumin of I "30" mg/l indicated increased risk of developing or having a genitourinary disorder. The sensitivity/specificity of the protein dipstick was 95.1%/95.5%, and the same for the albumin dipstick was 83.8%/93.8%. The cut-off for the albumin dipsticks probably should be set somewhat lower to reduce the number of false negatives and increase the sensitivity of the dipstick. When we compared the quantitative albumin to the protein dipsticks with the above cut-offs, we found the sensitivity/specificity to be 79.3%/94.4%, i.e., much like the albumin dipstick results. The many reports on the association of albuminuria and risk of renal disease recommend that screening should be done for albumin rather than protein. Based on the data from the school children, we estimate that a dipstick albumin of "30" mg/l is borderline increased risk, and that a protein dipstick of "150" mg/l is the same. If we call the dipstick "10" mg/l albumin, "30" mg/l albumin and the "150" mg/l protein results "low risk," then we estimate the prevalence of albuminuria in the school children to be about 2.1% and proteinuria to be about 4.3%. Children with these values should have a quantitative test for albumin and protein. We also tested a dipstick for creatinine and found increasing values with increasing age in both genders; the older boys had significantly higher creatinine values than the older girls and younger boys. For the albumin/creatinine ratio, we found 6028 children with a ratio of < 30 mg/g indicating low risk and 159 children with a ratio of > or = 30 mg/g indicating increased risk. The ratio may be more useful owing to the likely reduction of the number of false negatives and false positives.

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

A quantification of proteins of different molecular size has been shown to be useful in characterizing the mechanism and medical causes of proteinuria. By analyzing urine albumin, alpha1-microglobulin, immunoglobulin G and alpha2-macroglobulin together with total protein, prerenal, glomerular, tubular and postrenal causes of proteinuria can be detected and differentiated by their specific urine protein patterns. Using automated turbidimetric procedures, prerenal proteinurias are characterized by an albumin/total protein ratio below 0.4. Tubulo-interstitial diseases which are negative in the protein test strip procedure are detected and clearly differentiated from other causes of proteinuria by their high alpha1-microglobulin/albumin ratios. In post-renal proteinuria, alpha2-macroglobulin proved to be a useful marker, when albumin excretion exceeds 100 mg/l urine. This protein exhibits plasma-like ratios to albumin in postrenal causes, whereas it is much lower in renal proteinurias. The new strategy, which has been evaluated in more than 500 clinically and partly histologically proven cases of renal diseases, more sensitively detects glomerular and tubulo-interstitial diseases when applied in urine screening and allows us to distinguish all clinically important causes from analysis of a morning spot urine sample.