From a Urinalysis Strategy to an Evaluated Urine Protein Expert System

Urine single protein analysis has developed into a routine method for the screening and monitoring of kidney diseases. In order 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, a modular knowledge base was extracted in production rules and implemented in a modern expert system shell. The resulting interpretation system has been thoroughly verified and validated. After the need of interpretation of the complex findings had been documented in a survey, its usability in routine and its knowledge representation was evaluated in 11 hospitals. A user conference confirmed a high quality level of the reports proposed by UPES. It revealed that the problem of automatic data transfer as well as the common definition of diagnostic terms by laboratorians and clinicians play a crucial role for the use of knowledge-based systems in laboratory medicine.

[Unnecessary laboratory tests]

During the last 40 year medical laboratory tests per hospital stay have increased 12-fold. This is due to an increase of traditional test as well as by newly introduced analyses. Traditional markers of liver, heart and kidney diseases as well as tumor markers, markers of endocrine and metabolic disorders are critically analysed for regarding their medical needs. Assays which are no longer needed (aspartate aminotransferase, lactate dehydrogenase in heart infarction, acid phosphatase) are assessed differently from those ordered at the wrong time and too often (tumor markers, lipids, HbA (1c), thyroid hormones) and those whose indication has to be continuously renewed because of rapidly changing conditions (autoantibodies, marker of iron status, natriuretic peptides and gene analysis). The rapidly proceeding scientific and technical development allows to conclude, that even under strong and critical control of the medical needs the reduction of tests will contribute little to the further development of total costs of the medical laboratory.

Association of CSF apolipoprotein E, Abeta42 and cognition in Alzheimer's disease

A significant association between CSF Abeta42 and cognition in patients with Alzheimer's disease (AD) homozygous for the epsilon3 allele of the apolipoprotein E (apoE) has been described. In this study we extended our observations on apoE, as another plaque component, and investigated the association between CSF apoE concentrations and cognitive performance after stratification for the apoE genotype in 62 patients with AD, 19 other forms of dementia and 18 controls. CSF Abeta42 and apoE concentrations were significantly and positively associated with Mini Mental State Examination (MMSE) score in AD (Abeta42: r = 0.332; P = 0.026; apoE: r = 0.386; P = 0.006). For Abeta42 this association was exclusively present in epsilon3 homozygotes (r = 0.44; P = 0.014), whereas apoE was correlated with MMSE in epsilon4 hetero- or homozygotes subjects (epsilon4/epsilonX: r = 0.638; P = 0.004: epsilon4/epsilon4; r = 0.812; P = 0.05). No association was observed between CSF concentrations of Abeta42 and apoE. The significant relationship between MMSE and CSF Abeta42 in epsilon3 homozygotes and apoE in epsilon4 hetero- and homozygotes respectively may suggest that both proteins may be associated independently from each other with cognitive decline.

Influence of dehydration on glycerophosphorylcholine and choline distribution along the rat nephron

Glycerophosphorylcholine is one of the four major organic osmolytes in renal medullary cells, changing their intracellular osmolyte concentration in parallel with extracellular tonicity during cellular osmoadaptation. In this study, the tubular content of glycerophosphorylcholine was quantified in untreated and 48-h-dehydrated male rats. A chemiluminescence ultra-micromethod was developed to measure choline at the picomolar level in single tubules microdissected from collagenase-treated kidneys. The glycerophosphorylcholine level was calculated as the difference between total choline after acid hydrolysis and the free tubular choline content. In accordance with the glycerophosphorylcholine distribution pattern in different renal zones of untreated rats, low amounts of glycerophosphorylcholine were found in all cortical and outer medullary structures (< 35 pmol/mm), whereas increasing amounts were detected towards the papillary tip (163 pmol/mm). As a percentage of total choline, the level of free tubular choline varied from 4.2% in outer medullary proximal tubules to 30.3% in the inner medullary collecting ducts adjacent to the outer medulla (IMCD1). Antidiuresis led to a nearly twofold increase in glycerophosphorylcholine content in papillary collecting ducts. The osmolality-dependent regulation of organic osmolytes in single microdissected tubules has been demonstrated for the first time. Furthermore, the high tubular glycerophosphorylcholine concentration compared to sorbitol and myo-inositol emphasizes the predominance of glycerophosphorylcholine in the inner medulla and papilla of the rat kidney.

The role of automated urine particle flow cytometry in clinical practice

Urine particle flow cytometers (UFC) have improved count precision and accuracy compared to visual microscopy and offer significant labor saving. The absence of an internationally recognized reference measurement procedure, however, is a serious drawback to their validation. Chamber counting by phase contrast microscopy of supravitally-stained uncentrifuged urine is considered the best candidate for reference. The UF-100 (Sysmex Corporation, Japan) identifies RBC, WBC, squamous epithelial cells, transitional epithelial and renal tubular cells (SRC), bacteria, hyaline and inclusional casts, yeast-like cells, crystals and spermatozoa, using argon laser flow cytometry. Evaluations have established acceptable linearity over useful working ranges, with an imprecision that is consistently and significantly less than microscopy, and with negligible carry-over. Comparisons of UFC with chamber counts, quantitative urine microscopy, sediment counts, test strips, bacterial culture and urine density are reviewed. Clinical studies include diagnosis and monitoring of urinary tract infection; localization of the sites of hematuria; and diagnosis, monitoring and exclusion of renal disease. The most popular approach is to combine test strips with UFC for primary screening either always by both methods or by using test strips for analytes unrelated to particles analyzed by UFC. Expert systems now exist combining both test modalities based on user definable decision rules. The implementation of such a strategy significantly reduces microscopy review and saves time and expense without diminishing clinical utility.

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.

Towards European urinalysis guidelines. Introduction of a project under European Confederation of Laboratory Medicine

Improved standardized performance is needed because urinalysis continues to be one of the most frequently requested laboratory tests. Since 1997, the European Confederation of Laboratory Medicine (ECLM) has been supporting an interdisciplinary project aiming to produce European urinalysis guidelines. More than seventy clinical chemists, microbiologists and ward-based clinicians, as well as representatives of manufacturers are taking part. These guidelines aim to improve the quality and consistency of chemical urinalysis, particle counting and bacterial culture by suggesting optimal investigative processes that could be applied in Europe. The approach is based on medical needs for urinalysis. The importance of the pre-analytical stage for total quality is stressed by detailed illustrative advice for specimen collection. Attention is also given to emerging automated technology. For cost containment reasons, both optimum (ideal) procedures and minimum analytical approaches are suggested. Since urinalysis mostly lacks genuine reference methods (primary reference measurement procedures; Level 4), a novel classification of the methods is proposed: comparison measurement procedures (Level 3), quantitative routine procedures (Level 2), and ordinal scale examinations (Level 1). Stepwise strategies are suggested to save costs, applying different rules for general and specific patient populations. New analytical quality specifications have been created. After a consultation period, the final written text will be published in full as a separate document.

Human neutral brush border endopeptidase EC 3.4.24.11 in urine, its isolation, characterisation and activity in renal diseases

Human neutral brush border endopeptidase (NEP) was purified from the urine of patients suffering from acute toxic tubulointerstitial nephropathy. An enzyme preparation with specific activity of 102 Ug(-1) protein was obtained. The urinary activities of neutral endopeptidase and alanine aminopeptidase were measured in patients with renal disease and in 30 control patients, resulting in a reference range from 0.1 to 0.7 Ug(-1) creatinine and 1.4-14.1 Ug(-1) creatinine, respectively. Urine enzyme activities were highest in patients with acute tubulotoxic renal diseases. Neutral endopeptidase and alanine aminopeptidase activities were found to be 6.5- and 10-fold higher than the upper value of the reference range, respectively. Smaller increases in the rate of excretion of these enzymes (2.5- and 3.5-fold), respectively, were observed in patients suffering from acute tubular insufficiency and even lower increases, 2- and 1.5-fold, respectively, were observed in patients with chronic renal diseases. In diabetics and kidney transplant patients the enzyme excretion rates were within the reference range. Assay of both transmembrane metalloproteinases in urine may prove valuable in serving as markers for renal toxicity. Together with beta-NAG these enzymes could be employed as differentiation markers between acute and chronic tubular insufficiency.

External quality assessment of urine analysis in Europe. Results of a round table discussion during the symposium 'From uroscopy to molecular analysis', Seeon, Germany, September 18-20, 1999

Interlaboratory surveys on urine quantities have only recently been introduced in several European countries. Representatives of 10 European countries exchanged their experiences during an international urinalysis meeting held in September 1999. Although still not mandatory in most areas, more than 5000 laboratories participated in external quality assessment programs in the countries represented. Qualitative (test strips and microscopic morphology) as well as quantitative chemical and immunochemical quantities were included. The maximal allowable deviations are reported as well as methods used to determine target values. Consensus scales up to reference methods were applied. The participants agreed that quality criteria need to be defined separate from those already existing for plasma/serum analytes. Besides higher biological variables and different medical needs, less standardisation of methods to quantify urine constituents was observed as a major cause of higher interlaboratory differences.

Cerebrospinal beta-amyloid ((1-42)) in early Alzheimer's disease: association with apolipoprotein E genotype and cognitive decline

The concentration of beta-Amyloid ((1-42)) protein (Abeta42) in cerebrospinal fluid (CSF) was determined in 75 Alzheimer's disease (AD) patients, 35 patients with other causes of dementia and 30 cognitively healthy age-matched controls. A significant decrease of Abeta42 concentration was found in AD patients, even in 25 subjects with very mild dementia as compared to patients with other causes of dementia and controls. Within AD patients we observed a significant decline of Abeta42 from very mild to mild and moderate dementia. In addition, Abeta42 levels were negatively correlated with the severity of cognitive impairment and with the number of varepsilon4 alleles inherited. We conclude that measurement of Abeta42 in CSF might be helpful for identifying AD at an early stage and also for tracking the clinical course.

From a urinalysis strategy to an evaluated urine protein expert system

Urine single protein analysis has developed into a routine method for the screening and monitoring of kidney diseases. In order 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, a modular knowledge base was extracted in production rules and implemented in a modern expert system shell. The resulting interpretation system has been thoroughly verified and validated. After the need of interpretation of the complex findings had been documented in a survey, its usability in routine and its knowledge representation was evaluated in 11 hospitals. A user conference confirmed a high quality level of the reports proposed by UPES. It revealed that the problem of automatic data transfer as well as the common definition of diagnostic terms by laboratorians and clinicians play a crucial role for the use of knowledge-based systems in laboratory medicine.

Evaluation of pediatric nephropathies by a computerized Urine Protein Expert System (UPES)

A computerized Urine Protein Expert System (UPES) measuring creatinine, total protein, albumin, IgG, alpha(1)-microglobulin, alpha(2)-macroglobulin, and N-acetyl-beta-D-glucosaminidase, together with urine dipstick testing for granulocyte esterase and hemoglobin pseudoperoxidase, and measurement of serum creatinine had been found to be useful in adults for differentiating between renal disorders. The objective of this study was to investigate UPES for identifying the different types of proteinuria and their underlying prerenal, glomerular, tubular, and postrenal causes in 146 children characterized by routine and invasive nephrological investigations. UPES proved to be a useful tool in pediatric renal patients after refinements were implemented in the program. Comparing UPES with the pediatric nephrologist's interpretation of all available clinical and laboratory data, UPES diagnosed glomerulopathies in 46 (75%) of 61 patients. In a further 23% it suggested glomerular involvement by indicating either a disturbed glomerular permeability or increased excretion of albumin. Tubular proteinuria was correctly described by UPES in 23 (100%) patients with different tubulopathies. UPES revealed normal kidney function in all healthy children and all children with remission of renal disorders. Therefore, UPES can be regarded as a useful tool in the automated differentiation of renal diseases in children.

Preanalytical factors and their influence on analytical quality specifications

Whereas analytical standards are described by established quality control criteria, no such standards exist for defining the quality of the preanalytical phase. A working group of the German Society for Clinical Chemistry and Laboratory Medicine has defined recommendations to describe the quality criteria for materials and processes used in the diagnostic process between patients and the analytical step. Thus, the quality of the sample may be defined regarding its adequacy and amount, as well as anticoagulants and stabilizers used. Timing of sampling, transport and storage involve criteria on sample stability, proper transport and preanalytical treatment. Moreover, sample identification, storage, and handling of interference and influence factors can be documented in quality manuals for the preanalytical phase. These possible variables have been discussed in five European expert meetings and recommendations published in national journals and presented in book form.

Quality specifications for ordinal scale measurements with multiproperty (multiple) urine test strips

Analytical quality specifications for ordinal scale measurements have not been presented so far. Criteria are suggested for multiproperty (multiple) urine test strips based on upper limits of healthy reference intervals, analytical performance and statistical tests applicable to ordinal scales. Trueness (accuracy) can be evaluated against an acceptable comparison method by applying sensitivity and specificity concepts, and defining a grey zone with a lower detection limit and an upper confirmation limit. Concordance (agreement) of two or more ordinal scale categories should be evaluated by subtracting random agreement, using Kappa statistics. Repeatability (precision) can be calculated for categorized results using binomial statistics.

Opiate detection in saliva and urine--a prospective comparison by gas chromatography-mass spectrometry

There is an increasing interest in saliva as an alternative analytic body fluid.

OBJECTIVE

This study sought to determine the correlation of opiates analyzed in saliva and corresponding urine.

METHODS

A total of 130 adequate and 24 inadequate samples were collected from patients participating in drug withdrawal therapy. To obtain saliva from the oral cavity, a newly developed collection device (Clin Rep), consisting of a treated cotton roll and a centrifugation vial with a filter inset, was tested. For the preparation of a purified solution of urine, liquid extraction was used. Solid phase extraction was utilized to prepare the saliva samples. For the detection by gas chromatography-mass spectrometry, an appropriate derivatization was necessary using N-methyl-N-(trimethylsilyl)trifluoroacetamide. The retention times were compared with defined standard solutions. The obtained mass spectra showed a characteristic fragmenting pattern and offered a reliable identification.

RESULTS

The concordance of the analytic results of the saliva samples with urine was 93% for a decision limit of 100 ng/mL and 98% for a decision limit of 300 ng/mL (DHHS opiate cutoff) in urine.

CONCLUSIONS

Saliva, of adequate amount in 85% of samples, may be appropriate for analysis of drugs of abuse.

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.

Multicentre evaluation of KONE Optima analysis system

Optima from KONE Instruments Corporation is a new selective laboratory analyzer for turbidimetric, colorimetric and ion selective electrode measurements. Overall analytical performance of Optima and reagents provided by KONE was evaluated according to ECCLS guidelines, in a multicentre study involving four different laboratories, including substrates (cholesterol, high-density lipoprotein-cholesterol, creatinine), specific proteins (transferrin, IgG), enzyme activities (gamma-glutamyltransferase, alanine aminotransferase) and electrolytes (sodium, potassium, chloride). The results obtained attest good precision of the system for all the analytes tested: the range of within-run CV is 0.5 %-4.3 %, and range of between-day CV % is 0.8 %-7.9 % (median of four laboratories). Except for total cholesterol (5 % overestimation compared to the reference method) accuracy of measurement is adequate. Creatinine and uric acid assays were subjects of interference (defined as deviation > 10 % from target value) by bilirubin and haemoglobin respectively.

[Tau protein. A potential biological indicator for early detection of Alzheimer disease]

In 40 patients with Alzheimer's disease (AD), in 5 patients with non-AD dementia and in 36 cognitively normal controls the concentration of protein tau was determined in the cerebrospinal fluid (CSF). Of the AD patients, 19 were very mildly demented (MMSE score from 25 to 28). Even in these patients, CSF tau was significantly more elevated than in controls. In the non-AD patients protein tau was less increased. Among the AD patients there was no association between CSF tau and severity of cognitive impairment or deficit in cerebral blood flow, determined by SPECT. Our findings suggest that CSF tau may be elevated even at the predementia stage of AD and be useful as a biological marker for the early recognition of the disease.

Determination of lamotrigine, carbamazepine and carbamazepine epoxide in human serum by gas chromatography mass spectrometry

A method for the identification and quantification of the antiepileptics lamotrigine, carbamazepine and carbamazepine epoxide (active metabolite) in human serum is described. In refractory epilepsy the combination of carbamazepine and lamotrigine was recently developed to a modern therapeutic concept. The goal of this paper is therapeutic drug monitoring (TDM) of these substances. Serum was extracted with a quick precipitation method using a modified commercial extraction-kit and analysed by gas chromatography mass spectrometry (GC-MS). A gas-chromatographic temperature-pressure programme was developed that allowed the determination of lamotrigine by gas chromatography mass spectrometry. A reference spectrum of pure lamotrigine is herewith published for the first time. A new mass spectra library was created to support the identification of the antiepileptics in human serum. In the Specified Ions Monitoring mode (SIM) a detection limit below the therapeutic range and recoveries above 90% were obtained. Comparison of results obtained by GC-MS or a commercially available high performance liquid chromatographic (HPLC) method (for lamotrigine) and a fluorescence polarisation immunoassay (FPIA) (for carbamazepine) from spiked serum samples showed disagreement of no more than 10% between the methods and demonstrated the accuracy of the new method. In addition, quantitative determinations of these antiepileptics in samples from patients under anticonvulsive therapy showed a strong linear correlation with r2 = 0.961 for carbamazepine and r2 = 0.964 for lamotrigine. Only two from a total of 46 results differed by more than 10%. Our method for quantifying lamotrigine in serum seems to be highly specific and capable of measuring lamotrigine in patients on single therapy, as well as on add-on therapy with carbamazepine or carbamazepine epoxide. No interference from other coadministered drugs was detected.

Clinical chemistry in laboratory medicine in Europe--past, present and future challenges

European experts in clinical laboratory sciences have different backgrounds, and development of expertise in this field started more than 100 years ago. Specific national activities have created the heterogeneity that now exists amongst the academic professional membership of more than 40 scientific societies in Europe. The recent political changes have in addition contributed to the rapidly changing profile of Clinical Chemistry and related fields. Based on a questionnaire answered by 31 national representatives, the past, present and future aspects of the European Clinical Laboratory are reviewed. Of the more than 30,000 members of national societies, the majority studied medicine (40.1%), chemistry (27.2%) and pharmacy (21.1%) with large national differences in relative percentages. Post-graduate education is provided by two thirds of the national societies. In most European countries the same experts cover not only clinical chemistry but also haematology, haemostaseology, immunology and transfusiology. National quality assurance programmes are said to be established in 25 countries, but mandatory in only 11 of them. Of the future challenges, the implementation of request strategies were named most often, with interpretative reports and preanalytical aspects estimated as similarly important. It was thought that information technology and new scientific developments would make the greatest impact in the coming years, with economic pressure being the major limiting factor. Despite these limitations an increase in the number of tests is anticipated by most representatives, supporting the assumption of an increasing role of the clinical laboratory in future clinical medicine.

Kinetics and osmoregulation of Na(+)-and Cl(-)-dependent betaine transporter in rat renal medulla

Betaine is one of the major organic osmolytes that accumulate in the renal medulla in response to high extracellular tonicity. Recent studies in MDCK cells have shown that betaine is taken up by an Na(+)- and Cl(-)-dependent transporter located on the basolateral membrane. We demonstrate here the presence of Na(+)-Cl(-)-dependent betaine transporter(s) in tubule suspensions prepared from the rat outer and inner medulla. The betaine transport activity was two to three times higher in the inner medulla compared with the outer medulla. The removal of Na+ and Cl- reduced betaine uptake in the outer medullary tubules by 86% and 82%, respectively. The betaine uptake was decreased by 39% in hypotonic buffer (189 mosmol/ kgH2O) and increased by 82% in hypertonic buffer (545 mosmol/kgH2O), compared with isotonic buffer (308 mosmol/ kgH2O). Kinetic studies of Na(+)-dependent betaine uptake in the outer medullary tubules revealed both a low- and a high-affinity component as follows: low-affinity and high volume component with Michaelis constant (K(m)1) of 8.6 mM and maximal uptake rate (Vmax1) of 112 pmol.microgram protein-1.h-1; and a low-volume and high-affinity component with K(m)2 of 0.141 mM and Vmax2 of 10 pmol. microgram protein-1.h-1. To investigate whether the Na(+)-Cl(-)-dependent betaine transporter is regulated by tonicity in vivo, we quantitated its mRNA in rat renal cortex and outer and inner medulla using both canine and rat Na(+)-Cl(-)-dependent betaine transporter cDNA probes. A single band of 3.0 kb was seen in the Northern blots prepared from both outer and inner medulla, but not in the cortex. Water deprivation for 3 days increased the abundance of this mRNA in the outer and inner medulla by 140% and 170%, respectively, but did not affect its expression in the cortex. In conclusion, Na(+)-Cl(-)-dependent betaine transporter(s) is present in rat outer and inner medullary tubules, and betaine transporter mRNA abundance is regulated by the hydration state in vivo.

Site-specific regulation of organic osmolytes along the rat nephron

The regulation of organic osmolytes was investigated in acute furosemide and chronic lithium diuresis along the nephron and in urinary bladder of rats. Sorbitol, myo-inositol, glycerophosphorylcholine, and betaine were measured enzymatically or by high performance liquid chromatography in homogenates and bioluminometrically in microdissected tubules. In untreated rats, all osmolytes except myo-inositol increased along the corticopapillary axis. An efflux of all osmolytes (-50%) was observed in homogenates of outer and inner medulla after acute furosemide diuresis (15 min, urinary osmolality = 329 mosmol/kgH2O) and for both polyols in microdissected tubules (30 min). In urinary bladder, only low concentrations of myo-inositol were found not to be affected by furosemide treatment. Chronic lithium treatment (7 days; urinary osmolality = 385 mosmol/kgH2O) decreased inner medullary but not outer medullary osmolyte concentrations. The results confirm a site-specific organic osmolyte pattern along the rat nephron, which is rapidly changed in a segment-specific way by different mechanisms of diuresis. The bladder epithelium does not accumulate organic osmolytes because no "osmotic gap" exists across the basolateral membrane. The osmotic difference across the apical membrane is maintained by the apical tightness of these cells.

Development and evaluation of a urine protein expert system

Based on the quantitative determination of creatinine, total protein, albumin, alpha 1-microglobulin, IgG, alpha 2-macroglobulin, and N-acetyl-beta, D-glucosaminidase in urine in combination with a test strip screening, the findings of hematuria, leukocyturia, and proteinuria can be assigned to prerenal, renal, or postrenal causes. Using this graded diagnostic strategy as a knowledge base, we developed a computerbased expert system for urine protein differentiation ("UPES") as a decision-supporting tool. The knowledge base was implemented as a combination of "if/then" rules and two-step bivariate distance classification of marker proteins. The knowledge for this form of pattern recognition was derived from the results for a set of 267 patients with clinically and histologically documented nephropathies. To determine the diagnostic value of UPES, we tested another set of data: results for 129 urine analyses from 94 patients. Using these data, the system reached 98% concordance with the clinical diagnoses for the patients and was superior to the diagnostic interpretations of four human experts. UPES has been successfully integrated into the laboratory routine process, including automated data import.

Cerebrospinal protein tau is elevated in early Alzheimer's disease

Protein tau concentration was determined by an enzyme linked immunoassay (ELISA) in cerebrospinal fluid (CSF) of 22 patients with clinically diagnosed Alzheimer's disease (AD), in three patients with dementia caused by other neurological disorders (OND) and in 19 cognitively healthy controls. A significantly elevated protein tau concentration was found in AD patients as compared with controls, even in 11 patients with very mild dementia. There was no correlation between protein tau and the severity of cognitive impairment as assessed with the Mini Mental State Examination (MMSE). Tau concentrations were not or only slightly elevated in OND. We conclude that protein tau in CSF might be helpful as a biological marker for the early diagnosis of AD.

Intrarenal distribution of organic osmolytes in human kidney

The distribution pattern of renal organic osmolytes in surgically explanted human kidneys was investigated and compared with that of untreated Sprague-Dawley rats (Uosmo = 1186 mosmol/kg H2O). Sorbitol, myo-inositol, glycerophosphorylcholine and betaine were measured by liquid chromatography (HPLC) in homogenates of five different kidney zones from the cortex towards the papillary tip. All four organic osmolytes were detected as in human as in rat kidney. The expected increase from the inner medulla to the papillary tip for sorbitol and betaine, and from the outer medulla to the papilla for glycerophosphorylcholine, was observed in rats, but not in explanted human kidney. An inverse distribution pattern was observed with decreasing tissue contents from the inner and outer medulla to the papillary tip for all organic osmolytes and urea. This intrarenal osmolyte profile is in accordance with that observed during water and lithium diuresis in rats. Therefore it can be assumed that a loss of renal medullary osmolytes during the intra-operative treatment of patients led to the observed osmolyte pattern. We conclude that organic osmolytes are involved in renal medullary osmoadaptation of humans.

Determination of choline dehydrogenase activity along the rat nephron

A radioenzymatic microassay was developed to quantitate choline dehydrogenase activity in single microdissected nephron segments. This enzyme is the rate limiting step in the biosynthesis of betaine, which serves as an intracellular osmoregulatory organic solute in mammalian kidney. The enzyme localized in renal mitochondrial inner membrane forms betaine aldehyde, which in the assay is converted to betaine by oxidative treatment. A histochemical procedure based on the formazan detection of tetranitroblue tetrazolium chloride was applied in parallel. The results show that activities in proximal convoluted and straight tubules are more than 5 times higher (21 to 25 pmol h-1 mm tubule-1) compared to distal nephron segments with no significant differences along the proximal tubule. Along the osmotic gradient from the outer medullary towards the papillary structures enzyme activities increased in ascending limbs of Henle's loop and collecting tubules. Collecting ducts showed two times higher activities than ascending loop segments when corrected for tubular cell volumes. The quantitative data were confirmed by the histochemical procedure. The results allow for the conclusion that betaine synthesis is sufficient to build up renal betaine, but cannot explain the distribution pattern of betaine along the corticopapillary axis. Additional mechanisms like intrarenal and tubular transport have to be postulated.

A mathematical equation to differentiate overload proteinuria from tubulo-interstitial involvement in glomerular diseases

Determination of marker proteins like albumin and alpha 1-microglobulin allows to differentiate various types of proteinuria in kidney diseases. In the present communication we calculate the degree of tubulointerstitial involvement by quantitation of the tubular marker alpha 1-microglobulin in urine in relation to albuminuria. A mathematical relation between minimal tubular proteinuria with the degree of albumin excretion was observed. Cases forming this line did not exhibit interstitial fibrosis when analyzed histologically. In contrast most cases exhibiting higher excretion rates of the tubular marker showed various degrees of tubulointerstitial involvement. In order to differentiate interstitial contribution from overload tubular proteinuria in patients with an albumin excretion rate above 3000 mg/g creatinine alpha 1-microglobulin (measured) is suggested to be corrected by the "glomerular" component of alpha 1-microglobulin using the following equation: "tubulo-interstitial alpha 1-microglobulin" = alpha 1-microglobulin (measured) -4.7 exp (2.2 x 10(-4)) [albumin]. Alternatively the correction can be performed graphically. This procedure may be of considerable help in preventing misinterpretations of urinary protein patterns in patients with nephrotic proteinuria.

[Nephrological basis diagnosis in clinical practice]

The traditional urinalysis program, consisting of qualitative tests and the microscopical analysis of the urinary sediment, does no longer seem to be an adequate strategy to meet current medical quality requirements. New sensitive tests allow to exclude dysfunctions of glomerular and tubular function with hitherto unknown efficiency. This is possible by application of simple assays based on immunological techniques for albumin and alpha-1-microglobulin, which can be used in any medical office without technical equipment. Any finding of proteinuria, haematuria or leukocyturia may be differentiated by simple turbidimetric and microscopic procedures to separate renal from prerenal and postrenal causes. The new techniques have been successfully applied in early detection of renal complications in diabetics and hypertonics as well as immunological forms of renal disease. It is to be expected that the broader application of the new strategy helps to reduce many invasive investigations for the benefit of patients.

Diagnostic strategies in urinalysis

The traditional methods in urinalysis (visual microscopy, qualitative test strip screening) were compared with automated microscopy (UA-1000, TOA-medicals, Japan) and quantitative single protein analysis in 562 fresh morning urine samples. Albumin served as "glomerular" and alpha 1-microglobulin as "tubular" markers measured by turbidimetry. The test strip delivered at least one positive result in 60% of the urine for blood (21%), leukocytes (27%), or protein (34%). In only 4% casts or renal cells were found by traditional microscopy, whereas automated microscopy was positive for these findings in 28% of the urine. Quantitative urine protein analysis alone exhibited results outside the reference interval in 52% of the urine. Combination of the test strip procedure for blood and leukocytes with urine protein analysis increased the number of positives to 73%. Thirteen percent of these additional findings were classified as glomerular (64%) and tubular (72%) proteinurias. In 7% of the urine a false positive protein test strip result was confirmed by quantitative albumin determination. Of 157 urine samples, positive in mechanized video recorded screening, 60 (38%) were normal in single protein analysis. The results allow for the conclusion that the advanced techniques are superior to traditional screening procedures in detecting abnormal urine composition. It is suggested that traditional urinalysis should be supported or replaced by quantitative determination of albumin and alpha 1-microglobulin. This recommended strategy is able to exclude or detect tubulo-interstitial nephropathies or microalbuminuria in earlier phases of renal complications, such as in diabetes mellitus, hypertension or in nephrotoxic injury. A fully mechanized version is suggested to meet appropriate quality criteria and economic needs.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of human and rat kidney aldose reductase

In the present study we report on a rapid two-step affinity chromatographic procedure to purify aldose reductase from human and rat kidney papilla and inner medulla. This enzyme, which is responsible for sorbitol formation in the kidney, was purified 145-fold from rat and 76-fold from human kidneys by consecutive Blue Sepharose and Matrex Orange chromatography. SDS-PAGE showed a single band of 38 kD for the human enzyme and a doublet of similar molecular weight for the rat kidney aldose reductase. The enzyme was characterized by substrate specificity and kinetic constants found identical to that of other organs purified previously.

Differentiation of proteinuria and haematuria by single protein analysis in urine

Single proteins and tubular enzymes have been proposed as markers to detect and differentiate prerenal, glomerular, tubular, and postrenal forms of proteinuria and haematuria. By quantitation of total protein, albumin, alpha 1-microglobulin, IgG, alpha 2-macroglobulin, and N-acetyl-beta, D-glucosaminidase (beta-NAG) activity it has become possible to clearly separate these forms by analysis of a single sample of second morning urine. When this program was applied to screening of hospital patients, albumin, total protein, and NAG proved to be sufficient to exclude clinically relevant disturbances. alpha 1-Microglobulin was useful to separate primary glomerulopathies from tubulo-interstitial diseases. Glomerular and postrenal haematuria could be clearly separated by their different excretion rates of alpha 2-macroglobulin, when urine albumin concentration exceeds 100 mg/L. The results imply that wider application of these techniques can help to detect renal abnormalities at an earlier stage and differentiate the various forms by less invasive techniques.

Differentiation of human phospholipase A2 isoenzymes in serum and other body fluids with use of monoclonal antibodies

Elevated phospholipase A2 activities in serum were measured in patients suffering from acute pancreatitis or various inflammatory diseases. The photometric phospholipase A assay of Hoffmann & Neumann (Klin. Wochenschr. 67 (1989) 106-109) was combined with immunoabsorption by different monoclonal antibodies directed against pancreatic phospholipase A2. Pancreatic phospholipase A2 was purified from human duodenal juice. Monoclonal antibodies were prepared by fusion of spleen cells from immunized mice with P3X63-Ag8-653 myeloma cells. Samples with phospholipase A2 activity were incubated in monoclonal antibody-coated microtitre plates. Phospholipase A2 activities were determined in the monoclonal antibody-treated samples as well as in control samples. The method allows the determination of the fraction of human phospholipase A2 isoenzymes in various biological materials. For pancreatic phospholipase A2 the specific binding capacity was about 60-80%, the unspecific binding was 5-30%. Practically no cross-reactivity was seen with partially purified serum phospholipase A2, with recombinant platelet phospholipase A2, or with the sera of patients with non-pancreatic diseases. In conclusion, the present study confirmed the presence of pancreatic phospholipase A2 in human duodenal juice and in the ascites of necrotizing pancreatitis. However, pancreatic isoenzyme was absent in non-pancreatic inflammatory diseases. Therefore, elevated phospholipase activities in non-pancreatic inflammatory diseases cannot be attributed to the pancreas.

Osmolytes

The cells of the renal medulla osmotically adapt to chronic alterations in extracellular tonicity by appropriate changes in the intracellular contents of organic osmoeffectors. The major organic osmolytes are glycerophosphorylcholine, betaine, myo-inositol, sorbitol, and, possibly, taurine. When the concentrations of poorly permeant external solutes are acutely reduced, cells that have been adapted to high tonicities rapidly release organic osmolytes via specific transmembrane transport pathways. In contrast, when medullary cells are depleted of organic osmolytes, osmolyte accumulation on acute elevation of external tonicity is slow and involves stimulation of uptake, intracellular de novo synthesis, or inhibition of intracellular degradation, and is preceded by increased intracellular electrolyte concentrations. The available evidence suggests that this rise in intracellular ionic strength plays an important role in the initiation of those processes responsible for full adaptation of renal medullary cells to high tonicities. Recently, complementary DNAs encoding a myo-inositol and a betaine transporter have been isolated.

A new strategy for characterizing proteinuria and haematuria from a single pattern of defined proteins in urine

Prerenal, glomerular, tubulointerstitial and postrenal proteinurias and haematurias are usually differentiated by a number of non-invasive and invasive diagnostic procedures. We have applied a new analytical strategy based on the observation that different urine protein patterns are excreted in normal, prerenal, renal and postrenal proteinurias and haematurias. When analysed by turbidimetric procedures urine albumin, IgG, alpha 1-microglobulin and alpha 2-macroglobulin can be used as marker proteins to characterize the degree of glomerular permeability, tubular protein reabsorption and postrenal bleeding respectively. Primary glomerulopathies (selective and non-selective) and tubulointerstitial nephropathies can be differentiated by plotting the excretion rates of IgG or alpha 1-microglobulin against that of albumin. Postrenal contaminations are detected by quantitative turbidimetric assay of the high molecular weight proteins, alpha 2-macroglobulin and IgG. In postrenal bleeding, with albumin concentrations above 100 mg/l, the relative excretion rates of these proteins were proportional to their plasma concentrations. In glomerular haematurias, however, the ratios to albumin were much lower. The optimal discriminating ratio was found to be 2.0 x 10(-2) for alpha 2-macroglobulin/albumin and 2 x 10(-1) for IgG/albumin. Tubulointerstitial involvement in haematuria is characterized by elevated alpha 1-microglobulin excretion rates, with alpha 2-macroglobulin/albumin ratios below 2.0 x 10(-2) and IgG/albumin ratios above 2 x 10(-1). The reported procedure allows the exclusion and differentiation of clinically relevant proteinurias and haematurias in a single urine specimen.

Carbohydrate and lipid metabolism of the renal tubule in diabetes mellitus

Diabetic nephropathy not only involves vascular and glomerular changes but also affects tubular metabolism, structure and function. Under acute insulin withdrawal the tubular size increases with glomerular hyperfiltration. Insulin like growth factor 1 (IGF1) has been found to be a candidate mediator involved under these conditions. Tubular carbohydrate metabolism is characterized by gluconeogenesis in the proximal tubule, glycolytic enzymes in the distal segments and high aldose reductase activity in the structures of the renal papilla. In the diabetic state, gluconeogenesis is stimulated by changes of the acid base status. Mitochondrial glucose oxidation is decreased by inhibition of pyruvate dehydrogenase activity through preferential oxidation of fatty acids and ketone bodies. The increase in glycogen in distal tubule cells and sorbitol accumulated in papillary structures can be explained by the high extracellular glucose supply under diabetic conditions. Fatty acids taken up in excess of tubular energy needs accumulate in the nephron as triacylglycerols, mainly in the proximal convoluted tubule. Fatty acid oxidation is inhibited by ketone bodies in proximal and outer medullary tubules, leading to preferential oxidation of the latter under ketotic conditions. Ammonia formed during tubular metabolism of glutamine increases in metabolic acidosis but is suppressed by ketone bodies, leading to a nitrogen sparing effect of ketone bodies. All acute metabolic derangements are abolished, and normal metabolism reestablished by adequate insulin treatment in vivo.

Renal sorbitol, myo-inositol and glycerophosphorylcholine in streptozotocin-diabetic rats

The polyols, sorbitol and myo-inositol, seem to be involved in the development of diabetic complications of different organs. High concentrations of both polyols were found in kidney medulla in addition to trimethylamines. To investigate the influence of diabetes mellitus on the regulation of both polyols and glycerophosphorylcholine in kidney, these osmolytes were quantitated enzymatically along the corticopapillary axis in untreated, streptozotocin-diabetic and insulin-treated streptozotocin-diabetic rats. In control animals three individual osmolyte patterns were found: a steep gradient of sorbitol in the papilla, increasing amounts of glycerophosphorylcholine from the outer medulla to the papilla, and nearly equal amounts of myo-inositol in the renal medulla, decreasing towards the cortex. Diabetic rats exhibit an up to fourfold increase of inner medullary sorbitol, whereas myo-inositol was only elevated in the outer medulla. Glycerophosphorylcholine was lowered in the papillary tip and elevated in the outer medulla and cortex. Insulin treatment reduced sorbitol to a concentration between those of diabetic and control rats, caused a restoration of glycerophosphorylcholine in the papillary tip and outer medulla to control values, and increased cortical myo-inositol. These data confirm previous in vitro data, which show that papillary sorbitol specifically increases in hyperglycaemic states, thereby counteracting the increased extracellular tonicity due to elevated tissue glucose concentrations. Imbalance of extra- vs intracellular osmolality during insulin treatment may be involved in the pathomechanism of renal papillary necrosis.