Automated determination of urine and cerebrospinal fluid proteins with Coomassie Brilliant Blue and the Abbott ABA-100

Peritoneal Equilibration Test

Peritoneal transfer rates of urea, creatinine, glucose, protein potassium, and sodium as well as drain and residual volumes were measured during 103 equilibration tests performed in 18 diabetic and 68 nondiabetic patients. Equilibration test was performed over a 4-hour dwell exchange with 2 L of 2.5% Dianeal solution. Excellent reproducibility was seen after tests were standardized for length of preceding exchange, times of inflow and drainage, patient position, methods of obtaining and processing samples and laboratory assays. Diabetics did not have lower peritoneal solute transfers than nondiabetics. Wide variations were found in the study population.

Measurements of creatinine, glucose and sodium transfer were particularly useful in predicting the patient's response to the standard CAPO. The patients with highaverage peritoneal solute transport did well on standard CAPO even after losing residual renal function. Patients with high peritoneal solute transfer rates were likely to have inadequate ultrafiltration on standard CAPO. These patients did much better on dialysis modalities with short dwell exchanges, i.e. nightly peritoneal dialysis (NPO) or daytime ambulatory peritoneal dialysis (OAPO). Patients with low average, and particularly low peritoneal transport rates were likely to develop symptoms and signs of inadequate dialysis as their residual renal function became negligible, particularly in individuals with high body surface area.

Repeated tests were helpful in evaluating causes of insufficient ultrafiltration and/or inadequate dialysis.

Absent circadian rhythm of proteinuria in hospitalized patients with preeclampsia

OBJECTIVE

To study the variation of protein excretion in short-interval day-and-night collections in hospitalized preeclamptic patients on continuous bed rest.

METHODS

We prospectively studied 50 patients admitted to the hospital with the diagnosis of preeclampsia. Urine volumes in 2-, 4-, 12-, and 24-h durations were recorded. Protein concentrations in different volumes of urine were measured. Paired t-test was used to compare the volumes, concentrations, and the total amounts of protein in these samples of different durations.

RESULTS

There was no significant difference in the volume of urine and the concentration of proteinuria in the day when compared to night (12-h samples) (p > 0.05). The total amount of protein excreted was comparable for the two durations of samples. For shorter-duration collections (4- and 2-h), the difference in proteinuria between day and night samples remained blunted.

CONCLUSION

This study concludes that there is blunting of variation in protein excretion as observed in short-interval urine collections at different times of the day in hypertensive pregnant patients on continuous bed rest.

How should proteinuria be detected and measured?

Proteinuria is a classic sign of kidney disease and its presence carries powerful prognostic information. Although proteinuria testing is enshrined in clinical practice guidelines, there is surprising variation among such guidelines as to the definition of clinically significant proteinuria. There is also poor agreement as to whether proteinuria should be defined in terms of albumin or total protein loss, with a different approach being used to stratify diabetic and non-diabetic nephropathy. Further, the role of reagent strip devices in the detection and assessment of proteinuria is unclear. This review explores these issues in relation to recent national and international guidelines on chronic kidney disease (CKD) and epidemiological evidence linking proteinuria and clinical outcome. The authors argue that use of urinary albumin measurement as the front-line test for proteinuria detection offers the best chance of improving the sensitivity, quality and consistency of approach to the early detection and management of CKD.

Urinary proteomics: a tool to discover biomarkers of kidney diseases

There is intense interest in applying proteomics to urine analysis in order to promote a better understanding of kidney disease processes, develop new biomarkers for diagnosis and detect early factors that contribute to end-stage renal diseases. This interest creates numerous opportunities as well as challenges. To fulfill this task, proteomics requires, in its different stages of realization, various technological platforms with high sensitivity, high throughput and large automation ability. In this review, we will give an overview of promising proteomic methods that can be used for analyzing urinary proteome and detecting biomarkers for different kidney diseases. Furthermore, we will focus on the current status and future directions in investigating kidney diseases using urinary proteomics.

Protein concentration of cerebrospinal fluid by precipitation with Pyrogallol Red prior to sodium dodecyl sulphate-polyacrylamide gel electrophoresis

The Pyrogallol Red Molybdate (PRM) and Coomassie Brilliant Blue (CBB) protein dye-binding assays have been applied to samples of cerebrospinal fluid (CSF) to investigate protein concentration by dye precipitation prior to sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The protein concentration values of the CSF samples (N=62) showed good agreement between the PRM and CBB assays as indicated by linear regression analysis (y(PRM)=1.033x(CBB)+1.004 in units of mg/l, r=0.99) but the PRM assay was optimal for protein concentration as the PRM protein-dye complex was less soluble allowing protein recovery over a wider working range. Dye precipitation using PRM is recommended as a simple, rapid and economic method for protein concentration of samples of CSF prior to SDS-PAGE.

Two-hour urine collection for evaluating renal function correlates with 24-hour urine collection in pregnant patients

OBJECTIVE

We sought to determine if 2-h urine collection for the assessment of urine protein excretion and creatinine clearance correlates with 24-h urine collection in pregnant patients with renal disease.

METHODS

We enrolled patients of gestational ages ranging from 8-41 weeks, admitted as inpatients and having undergone evaluation for renal function (n = 59). We obtained the following samples: 1) 2-h urine, and 2) 24-h urine. We measured serum creatinine concentration, urinary protein, creatinine concentration, and creatinine clearance. The data was analyzed using descriptive analysis, two-way ANOVA, univariate linear regression analysis, and Bland-Altman plot comparing the efficacy of 2-h urine results with 24-h urine results.

RESULTS

We analyzed the data on 51 patients. Total proteinuria calculated by protein/creatinine (P:C) ratio in the 2-h group correlated with the total protein measured in the 24-h group (1,840.8 +/- 786 and 1,944 +/- 1,060 mg [mean +/- SE], respectively, r2 = 0.95, P < 0.0001). Creatinine clearance correlated in the 2- and 24-h groups (111 +/- 42 and 122.5 +/- 50 ml/min, respectively; r2 = 0.73, P < 0.001).

CONCLUSION

Two-hour urine sampling offers the same clinical information as 24-h urine collection for the evaluation of renal function. Use of 2-h urine collection reduces the time of evaluation and diagnosis, whereby increasing patient compliance and reducing errors in performance of the tests.

Total Protein Determination in Urine: Elimination of a Differential Response between the Coomassie Blue and Pyrogallol Red Protein Dye-binding Assays

Background: The total protein content of urine is a good index of renal function, but its determination is unreliable. Protein dye-binding assays are simple, but they characteristically lack a uniform response to different proteins.

Methods: We investigated a differential response of the Sigma Microprotein Coomassie Brilliant Blue (CBB) and Pyrogallol Red-molybdate (PRM) protein dye-binding assays to urine, using human albumin, albumin/globulin, or urinary protein as calibrator.

Results: The urine protein values (n = 60) obtained with the CBB assay were 110–13 500 mg/L (mean, 2390 mg/L) compared with 160–18 300 mg/L (mean, 3470 mg/L) obtained with the PRM assay (CBB:PRM protein concentration ratio, 0.46–0.88, mean, 0.69 ± 0.10). The differential response was highly reproducible as indicated by Sigma urine control Level 1 (within-day CBB:PRM ratio, 0.68 ± 0.02; between-day CBB:PRM ratio, 0.67 ± 0.04) and Sigma urine control Level 2 (within-day CBB:PRM ratio, 0.60 ± 0.01; between-day CBB:PRM ratio, 0.59 ± 0.02). The use of urinary protein as a calibrator (rather than human albumin) greatly improved the agreement between the assays when applied to urine (yCBB = 0.972xPRM − 16 vs yCBB = 0.685xPRM + 17). In studies using urine controls, this calibrator also improved agreement between the CBB, PRM, trichloroacetic acid (TCA), and benzethonium chloride protein methods and, to a lesser extent, agreement with the TCA-Ponceau S method.

Conclusion: The use of a urinary protein calibrator improves the agreement between different methods used to determine total protein in urine.

Electrophoretic analysis of Bence Jones proteinuria

The electrophoresis of Bence Jones proteinuria (BJP) by urinary protein electrophoresis (UPE), immunoelectrophoresis (IE), immunofixation electrophoresis (IFE), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing (IEF), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) is described. UPE, IE and IFE are briefly discussed as clinical laboratory methods for the detection and typing of free light chain (LC) whilst the high resolution electrophoretic methods (SDS-PAGE, IEF, 2-DE and CE) are considered in greater detail as research tools for molecular characterisation of free LC and its association with nephrotoxicity. Refinements of sample processing designed to improve the standardisation of analysis of BJP by high resolution electrophoretic methods are reported.

Infusion of plasma expanders may lead to unexpected results in urinary protein assays

Overt proteinuria was detected in the urine of a potential kidney donor, ultimately leading to the refusal of the kidneys for transplantation purposes. Histological examination of the kidneys did not reveal any abnormalities. Searching for substances that could have interfered with the urinary total protein assay, the role of infused, modified gelatin plasma expanders was investigated. We therefore measured the concentration of protein before and after the addition of various artificial plasma expanders to urine. Only when Biuret reagent or Pyrogallol Red dye were used did we find elevated concentrations of protein. Other methods, including the turbidimetric assays, did not detect additional amounts of protein in the spiked urine. We conclude that the infusion of modified gelatin solutions may cause apparent proteinuria. This effect is not observed with starch-based plasma expanders. Clinical chemists and clinicians should be aware of this phenomenon and possibly repeat the analysis with a different technique.

Clinical analysis of human urinary proteins using high resolution electrophoretic methods

The application of isoelectric focusing (IEF), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) for high resolution electrophoretic analysis of human urinary proteins is reviewed. In each case, the information is tabulated chronologically with details of sample preparation, electrophoretic system, detection method and clinical application. The text includes an historical perspective of the use of each method for urinalysis and a detailed review of the application of the methods to the investigation of renal disease, renal transplantation, Bence Jones proteinuria (BJP), diabetes mellitus, cadmium toxicity, nephrolithiasis and cancers of the urogenital tract.

Automated quantitation of total protein in cultured skin fibroblasts

An automated Coomassie Blue method of measuring total protein in cultured skin fibroblasts using a random access analyzer, the Roche MIRA, was compared to a manual dye binding method using bicinchoninic acid. The automated Coomassie Blue method is in common use in many routine laboratories for measurement of total protein in urine and CSF, and was found by us to be significantly faster than a manual protein method, with an average assay time of 2 min per sample. In addition, intra- and inter-run precision were comparable for the automated and manual methods, and compared favourable with other automated methods. We recommend that where the MIRA apparatus is available, consideration be given to its use for protein quantitation of cell or tissue extracts.

Assessment of renal function during pregnancy using a random urine protein to creatinine ratio and Cockcroft-Gault formula

The current standard for assessment of renal function in pregnant women is a 24-hour urine collection to determine creatinine clearance and proteinuria. It is easier to use the random urine protein to creatinine (P:C) ratio and the Cockcroft-Gault (CG) formula to estimate protein excretion and glomerular filtration rate, but the reliability of these formulae in combination for assessing renal function in pregnant women with renal disease is unknown. We compared the results of the P:C ratio with the 24-hour urinary protein excretion and the results of the CG clearance estimate with the 24-hour urine creatinine clearance in 34 pregnant women with underlying renal disease. Comparisons were made once in each trimester and postpartum. Prepregnancy weights were used in the CG formula: (140 - age x weight [kg] x 0.85)/72 x serum creatinine (mg/dL). Twenty-six first trimester, 33 second trimester, 21 third trimester, and 15 postpartum comparisons were made for creatinine clearance and 16 first trimester, 29 second trimester, 15 third trimester, and 15 postpartum comparisons were made for protein excretion. Measured creatinine clearance for the three trimesters combined (105 +/- 40 mL/min [mean +/- SD]) correlated significantly with CG clearances (113 +/- 52 mL/min; r = 0.87). The mean P:C values (2.03 +/- 3.15) for the three trimesters combined correlated significantly with 24-hour urine protein (2.25 +/- 4.21 g; r = 0.92). Our study demonstrates excellent correlations between the CG formula using prepregnancy weights and 24-hour creatinine clearance and between the P:C and 24-hour urinary protein in this population.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteinuria--what value is the dipstick?

The value of the urinary dipstick in the assessment of proteinuria was investigated in a study correlating laboratory measurements of protein and albumin against the dipstick protein in the same samples of urine; 94 patients (100 admissions) were studied at the Royal Air Force Renal Unit, each patient collecting two 24-h urine samples. Along with each 24-h sample, 10-ml aliquots of urine were obtained at 3 designated times during the day for both ward dipstick testing and laboratory assay; + or more on the dipstick correlated with abnormal proteinuria (greater than or equal to 150 mg/24 h) in 88% of cases, whilst trace values straddled the level of significant proteinuria. Further differentiation of trace was possible by repeat testing during the day. The subsequent presence of a dipstick negative during that day correlated with normality in all but 5% of cases. In order to ensure detection of renal disease presenting as isolated orthostatic proteinuria, assay of the mid-morning sample is recommended.