Measurement of the albumin content of urinary protein using dipsticks

Urinary strips for protein assays: easy to do but difficult to interpret!

Urine samples can be readily obtained from patients in everyday clinical practice. Therefore, the availability of urine allows physicians to obtain relevant clinical information in a timely manner. Since the measurement of urinary protein levels is essential in diagnosing and treating a host of diseases, the potential detection of urinary proteins by urinary strips in an easy, quick, and cheap way is very attractive. However, to ensure optimal use of urinary strips, one needs to be aware of their characteristics and their limitations. In this review, we discuss the characteristics of the urinary strips available for testing urinary protein levels and for detecting urinary albumin. We then consider their analytical performances in their most widely used clinical applications (e.g., in pregnancy, chronic kidney disease, diabetes, and screening of the general population).

Fabrication of paper microfluidic devices using a toner laser printer

This paper describes a method to fabricate microfluidic paper-based analytical devices (μPADs) using a toner laser printer. Multiple methods have been reported for the fabrication of μPADs for point-of-care diagnostics and environmental monitoring. Despite successful demonstrations, however, existing fabrication methods depend on particular printers, in-house instruments, and synthetic materials. In particular, recent discontinuation of the solid wax printer has made it difficult to fabricate μPADs with readily available instruments. Herein we reported the fabrication of μPADs using the most widely available type of printer: a toner laser printer. Heating of printed toner at 200 °C allowed the printed toner to reflow, and the spreading of the hydrophobic polymer through the filter paper was characterized. Using the developed μPADs, we conducted model colorimetric assays for glucose and bovine serum albumin (BSA). We found that heating of filter paper at 200 °C for 60 min caused the pyrolysis of cellulose in the paper. The pyrolysis resulted in the formation of aldehydes that could interfere with molecular assays involving redox reactions. To overcome this problem, we confirmed that the removal of the aldehyde could be readily achieved by washing the μPADs with aqueous bleach. Overall, the developed fabrication method should be compatible with most toner laser printers and will make μPADs accessible in resource-limited circumstances.

We developed a method to fabricate microfluidic paper-based analytical devices (μPADs) using a toner laser printer. We addressed a potential problem of pyrolysis that resulted from long duration of heating required for the penetration of the toner.

Methods of albumin estimation in clinical biochemistry: Past, present, and future

Estimation of serum and urinary albumin is routinely performed in clinical biochemistry laboratories. In the past, precipitation-based methods were popular for estimation of human serum albumin (HSA). Currently, dye-binding or immunochemical methods are widely practiced. Each of these methods has its limitations. Research endeavors to overcome such limitations are on-going. The current trends in methodological aspects of albumin estimation guiding the field have not been reviewed. Therefore, it is the need of the hour to review several aspects of albumin estimation. The present review focuses on the modern trends of research from a conceptual point of view and gives an overview of recent developments to offer the readers a comprehensive understanding of the subject.

The prevalence and risk factors of microalbuminuria in hypertensive patients under current medical treatment

OBJECTIVE

A link between urinary albumin excretion and an increased incidence of cardiovascular mortality has already been demonstrated. However, the reported prevalence of microalbuminuria (MAU) in patients with hypertension is highly variable. We therefore aimed to conduct a cross-sectional multicenter study to investigate the prevalence of urinary albumin excretion in treated hypertensive patients in our current practice.

METHODS

A total of 1,258 hypertensive patients were enrolled in this study. Patients with macroalbuminuria were excluded. The concentrations of urinary microalbumin and creatinine were measured. Urinary albumin excretion was expressed as the ratio of albumin to creatinine excretion.

RESULTS

The mean systolic and diastolic blood pressures were 130.9±12.7 mmHg and 74.7±8.9 mmHg, respectively. The overall prevalence of MAU was 42.8%, and it was observed in 35.8% of patients treated with a single medication. Patients with polyvascular disease exhibited a higher prevalence of MAU compared with patients with monovascular disease. The factors related to the presence of MAU included the estimated glomerular filtration rate (eGFR), systolic blood pressure, and glycated hemoglobin (HbA1c) level (odds ratios [ORs] of 0.988, 1.026, and 1.371, respectively).

CONCLUSION

The present study showed that the prevalence of MAU among hypertensive patients was 42.8%, even in patients whose blood pressure was relatively well controlled. Additionally, the eGFR, systolic blood pressure, and HbA1c level are risk factors for the development of MAU. These findings suggest that a substantial number of hypertensive patients have MAU and highlight the importance of strictly controlling these factors to improve patient prognosis.

Variation in the Urinary Protein/Creatinine Ratio at Four Different Periods of the Day in Hypertensive Pregnant Women

OBJECTIVE

To assess the urine protein/creatinine ratio in urine samples of pregnant women with hypertension in regard to: 1) the presence of significant variation at different periods of the day; 2) the differences if they exist, to identify the most reliable period of the day for sampling; and 3) whether the first sample, obtained when the patient arrives at the clinic, correlates with the same accuracy, with the 24-hour proteinuria.

DESIGN

Cross-sectional study.

PLACE

Obstetrics Emergency Department, Hospital de Clínicas de Porto Alegre, a teaching hospital in Porto Alegre, Brazil.

POPULATION

Seventy-five women with hypertension with 20-week gestation or over.

METHODS

Urine samples for determination of the protein/creatinine ratio were obtained on arrival (first specimen) and every 6 hours thereafter, totaling four samples in 24 hours. Four sampling periods were established: 1) from 8 am to 2 pm, 2) from 2 pm to 8 pm, 3) from 8 pm to 2 am, and 4) from 2 am to 8 am. The protein/creatinine ratio in the four different day periods were compared with the 24-hour proteinuria obtained simultaneously. The results were analyzed by the Spearman correlation and the receiver-operator characteristic (ROC) curve.

RESULTS

The urine protein/creatinine ratio is strongly correlated (Spearman correlation equal to 0.8 or greater) with the 24-hour proteinuria at all four periods of the day (p<0.001), as well as the first sample obtained on arrival (p=0.003). These findings were corroborated by the ROC curve in which the values of four day periods and that of the first sample were equal to or greater than 0.930.

CONCLUSION

In hypertensive pregnant women, the single voided urine sample protein/creatinine ratio, irrespective of sampling time, is strongly correlated with the 24-hour proteinuria, as is the sample obtained on arrival.

Low-cost printing of poly(dimethylsiloxane) barriers to define microchannels in paper

This paper describes the use of a modified x,y-plotter to generate hydrophilic channels by printing a solution of hydrophobic polymer (pol(dimethylsiloxane; PDMS) dissolved in hexanes onto filter paper. The PDMS penetrates the depth of the paper and forms a hydrophobic wall that aqueous solutions cannot cross. The minimum size of printed features is approximately 1 mm; this resolution is adequate for the rapid prototyping of hand-held, visually read, diagnostic assays (and other microfluidic systems) based on paper. After curing the printed PDMS, the paper-based devices can be bent or folded to generate three-dimensional systems of channels. Capillary action pulls aqueous samples into the paper channels. Colorimetric assays for the presence of glucose and protein are demonstrated in the printed devices; spots of Bromothymol Blue distinguished samples with slightly basic pH (8.0) from samples with slightly acidic pH (6.5). The work also describes using printed devices that can be loaded using multipipets and printed flexible, foldable channels in paper over areas larger than 100 cm2.

Inefficacité des bandelettes urinaires dans la recherche de néphropathie incipiens chez les diabétiques

INTRODUCTION

Microalbuminuria is an early indication of diabetic nephropathy in patients with Type 1 diabetes and a marker of cardiovascular in patients with type 2 diabetes. It must therefore be assessed annually in these patients. We sought to determine whether semiquantitative determination of proteinuria with urinary dipsticks was useful for this purpose.

METHOD

This analysis of consecutive urinary samples among diabetic patients excluded those with dipstick results positive either for leukocyturia or nitrituria, to avoid false positives due to urinary infection. We assessed the reliability of the dipsticks in comparison with conventional microalbuminuria and proteinuria assays.

RESULTS

The study included 230 patients. Positive dipstick results had good positive (95.7%) and negative (93.9%) predictive values. Low levels of microalbuminuria, however - those that lead to early adjustment of treatment, were much more difficult to identify: the negative predictive value was only 73.7% and proteinuria was no longer correlated with microalbuminuria.

DISCUSSION

Urinary dipsticks cannot replace conventional assays for microalbuminuria or proteinuria.

Surface-enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS): a new proteomic urinary test for patients with urolithiasis

SELDI-TOF-MS is a highly sensitive protein-analysis tool capable of detecting minute protein profile differences between biological samples. As proteins have been associated with urinary tract calculi, protein-based urinalysis may offer insights into their diagnosis. The purpose of this study was to evaluate SELDI-TOF-MS as a potential method for identifying urinary biomarkers of urolithiasis. Midstream sterile urine samples were obtained from 25 male patients with a confirmed diagnosis of urolithiasis (test group) and 25 male subjects with no known history of the disease (controls). Urinary levels of oxalate, total protein, albumin, and osteopontin were determined. Protein profiles were generated using SELDI-TOF-MS.SELDI-TOF-MS profiling revealed a relationship between protein peak intensities at 67 and 24 kDa that differed between the two groups. The ratio of p67:p24 was found to be less than 1.0 in all of the control samples (mean 0.26), while 18 out of 25 (72%) of the test group samples displayed a ratio greater than 1.0 (total group mean 4.75, P<0.001). Albumin, total protein, and oxalate levels were higher in the test group than the controls. Although SELDI-TOF-MS is not yet in widespread use in hospital and diagnostic laboratories, this system represents a promising new method for rapidly identifying patients with urolithiasis.