Comparison of instrument-read dipsticks for albumin and creatinine in urine with visual results and quantitative methods

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).

A versatile probe for serum albumin and its application for monitoring wounds in live zebrafish

A versatile probe for serum albumin and its application in monitoring wounds in live zebrafish.

Diagnostic accuracy of urine dipstick testing in screening for microalbuminuria in type 2 diabetes: a cohort study in primary care

BACKGROUND

Clinical guidelines recommend annual screening for microalbuminuria in diabetes. Detection of microalbuminuria is important because it is associated with increased morbidity and mortality. Dipstick tests for microalbuminuria may be convenient, but their accuracy is uncertain.

OBJECTIVE

To assess the utility of urine dipstick testing for microalbuminuria in type 2 diabetes.

METHODS

In a 6-week cohort study in four general practices in Oxfordshire, UK, first-pass urine samples were obtained at two weekly intervals from patients with type 2 diabetes and tested in the practice using Micral-Test and Microalbustix urine dipsticks. Parallel samples were sent for laboratory albumin-creatinine ratio (ACR) assay. Results of single dipstick tests and sequences of dipstick and laboratory tests were compared with a clinical testing strategy based on current guidelines to assess the accuracy and estimate costs of testing.

RESULTS

The prevalence of microalbuminuria was 12.5% (n = 88). Mean (standard deviation) age was 68 (10) years, 56 (57%) were men. Median (interquartile range) diabetes duration was 6.2 (2.0-10.0) years. The sensitivity and specificity, respectively, of a single Micral-Test were 91.7% and 44.0% and of a Microalbustix test 33.3% and 92.0%. Testing strategies involving dipstick and laboratory ACR measurements or dipstick tests had similar accuracy. The costs of using dipstick tests were overall lower than laboratory ACR-based testing.

CONCLUSIONS

Dipstick testing in this study did not reliably identify diabetes patients with microalbuminuria. Although dipstick testing would decrease testing costs, it could either fail to diagnose most patients with microalbuminuria or increase the numbers of patients retested depending on the dipstick used.

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

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

Renal safety of intensive cholesterol-lowering treatment with rosuvastatin: a retrospective analysis of renal adverse events among 40,600 participants in the rosuvastatin clinical development program

OBJECTIVE

Intensive lowering of low-density lipoprotein cholesterol (LDL-C) with statins reduces cardiovascular risk but can cause liver-, muscle-, and possibly renal-related adverse events (AEs). We assessed the effects of rosuvastatin on the risk of developing renal impairment or renal failure among participants in the rosuvastatin clinical development program.

METHODS

The analysis was based on AE data reported by investigators from 36 studies that included 40,600 participants who did not have advanced, pre-existing renal disease. Rates of renal AEs were determined based on time to first occurrence of renal impairment or renal failure.

RESULTS

Renal impairment or renal failure was reported in 536 study participants during 72,488 patient-years of follow-up. Renal event rates were higher in patients with history of heart failure (n = 5011), hypertension (n = 21,864), diabetes (n = 5165), or estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m(2) (n = 9507) at baseline but did not differ with rosuvastatin compared with placebo or with rosuvastatin 40 mg compared with rosuvastatin 10mg. Relative risk (RR) estimates obtained from pooled analysis of placebo-controlled trials were RR: 1.03 (95% CI: 0.86-1.23, p = 0.777) for any reported renal impairment or renal failure event, RR: 1.02 (95% CI: 0.76-1.37, p = 0.894) for serious renal AEs, and RR: 0.70 (95% CI: 0.36-1.35, p = 0.282) for renal AEs leading to death.

CONCLUSION

These findings suggest that intensive LDL-C-lowering treatment with rosuvastatin does not affect the risk of developing renal insufficiency or renal failure in patients who do not have advanced, pre-existing renal disease.

Influence of the Ginkgo extract EGb 761 on rat liver cytochrome P450 and steroid metabolism and excretion in rats and man

Extracts from leaves of Ginkgo biloba L. are among the most used herbal medicinal products worldwide. Based on in-vitro tests and studies in rats, concern has been expressed that intake of Ginkgo extracts may affect hepatic metabolism of xenobiotics and cause drug interactions, although no evidence for modulation of cytochrome P450 (CYP450) enzyme activity was obtained in human trials. Because of these contradictory findings, we investigated the effects of the standardised extract EGb 761 on hepatic CYP450 in rats. EGb 761 (100 mg kg−1 daily, p.o., for 4 days) strongly increased liver CYP450 content and altered the ex-vivo biotransformation of androstendione, as well as metabolism of endogenous steroids. However, in human subjects no effect on the urinary steroid profile was observed after intake of EGb 761 for 28 days (240 mg daily). These results indicate that the effects of EGb 761 on drug metabolising enzymes are specific for rats and may not be extrapolated to man.

Biomonitoring human exposure to organohalogenated substances by measuring urinary chlorophenols using a high-throughput screening (HTS) immunochemical method

The widespread contamination of the environment by persistent organochlorinated substances is well-known. High-throughput immunochemical methods may improve routine assessment of the exposure of the population to these chemicals by analyzing urinary biomarkers. Trichlorophenols (TCP) have often been considered as biomarkers of many organochlorinated compounds. With the aim to assess exposure of the population to these substances a high-throughput immunosorbent solid-phase extraction (HTS-IS-SPE) procedure coupled to ELISA for simultaneous analyses of 2,4,6-TCP immunoreactivity equivalents (2,4,6-TCP-IR equiv) in multiple hydrolyzed urine samples has been developed. Around 100 urine samples can be processed simultaneously with an inter- and intraassay precision lower than 23% CV and a limit of detection of 0.3 microg L(-1). The analyses by HTS-IS-SPE-ELISA and HTS-IS-SPE-GC/MS of urine samples (N = 117) collected from three different population groups point to a broad exposure of the Catalonian population to organohalogenated substances including the recently emerging organobrominated pollutants. Environment and edible products seem to be the most likely sources of exposure, since excretion of 2,4,6-TCP-IR equiv has been found to be independent from the occupational sector. An excellent correlation was observed between the 2,4,6-TCP-IR equiv determined by HTS-IS-SPE-ELISA and the concentrations measured by HTS-IS-SPE-GC/MS (R2 = 0.912). The results show that immunochemical screening methods, based on the quantification of urinary biomarkers, can be excellent tools for exposure assessment. The HTS-IS-SPE-ELISA presented here has proved to be efficient, precise, accurate, rapid, and specific, which opens up the possibility for a broad variety of applications where routine testing of large number of samples is required.

Using protein/creatinine ratios in random urine

We assessed the new test paper Multistix PRO IOLS, in which the +/-region of the conventional test for protein was altered so that creatinine correction became possible. Urinary samples from 235 patients with various renal diseases were obtained from the Juntendo University Hospital. We examined 1) the correlation between qualitatively measured values of urinary protein by the new test paper and the conventional test paper, and 2) the correlation between qualitative and quantitative values of protein (P), creatinine (C), and the P/C ratio measured by the new test paper. There was a good correlation between the P/C ratio observed with the new test paper and that observed by quantitative analysis. There was also a good correlation of the P/C ratio between 24-hr urine and urinary samples obtained at any time of day. Thus, it appears that the results obtained from urinary samples any time of day can predict the amount of protein excreted during the day.

Diabetes Mellitus Non-Glucose Monitoring: Point-of-Care Testing

OBJECTIVE:

To review and evaluate reimbursable point-of-care testing devices yielding immediate results, other than glucometers, that are available to evaluate and monitor diabetes and its complications and to describe how pharmacists may use these devices.

DATA SOURCES:

A MEDLINE search (1966-March 2003) was performed using the following search terms: point-of-care systems, clinical diabetes monitoring, decision support systems, glycosylated hemoglobin, and microalbumin. Pertinent company and product Web sites and customer service departments were accessed for information about point-of-care devices and supplies.

STUDY SELECTION AND DATA EXTRACTION:

All descriptive, evaluative, and comparative articles and product information were reviewed, and relevant information was included.

DATA SYNTHESIS:

Diabetes mellitus is a complex, chronic metabolic disease that is a challenging management problem and requires routine monitoring for disease control and screening for complications. Point-of-care tests are available to monitor hemoglobin A1c, glucose, fructosamine, ketones, lipid profiles, urinary microalbumin concentrations, and alanine aminotransferase concentrations. Many of these tests are Clinical Laboratory Improvement Amendments (CLIA)—waived and, therefore, practical for pharmacists to use in a variety of settings. Tests for measuring sensation are also discussed. Pharmacists should consider each of these tests in the establishment of a comprehensive diabetes care service.

CONCLUSIONS:

The availability of many new point-of-care testing methods creates new opportunities for pharmacists to monitor drug therapy and screen for complications in patients with diabetes. Reimbursement is possible since many of these tests are CLIA-waived.

Rosuvastatin-induced arrest in progression of renal disease

Preclinical and limited clinical data suggest that statins decrease the progressive decline in renal function that occurs in patients with renal disease. Pooled analysis of data obtained from a population of hyperlipidemic patients enrolled in the rosuvastatin (Crestor) clinical development program permitted assessment of its effects on renal function both early and later in the course of treatment. Study participants were initially included in controlled clinical trials that evaluated the lipid-lowering efficacy and safety of rosuvastatin when compared with placebo or other lipid-lowering agents (i.e., atorvastatin, simvastatin, pravastatin, cholestyramine, fenofibrate or extended-release niacin). The median duration of treatment with the various doses of statins in these trials was approximately 8 weeks. Following completion of a controlled clinical trial, patients were permitted to enter an open-label extension trial and received rosuvastatin treatment. These data permitted assessment of renal function in a diverse group of over 10,000 patients who received rosuvastatin in its recommended dose range (5-40 mg) for up to 3.8 years. Mean serum creatinine concentrations were lower when compared with baseline both early and later in the course of rosuvastatin treatment. In contrast, no change in mean serum creatinine was observed with placebo. Mean glomerular filtration rates (GFR) predicted from the Modification of Diet in Renal Disease (MDRD) equation were higher when compared with baseline both early and later in the course of rosuvastatin treatment. No change in GFR was observed in the placebo group. Among patients who received long-term rosuvastatin treatment (> or =96 weeks), GFR was unchanged or tended to increase, rather than decrease, when compared with baseline irrespective of age, gender, hypertensive or diabetic status, level of renal function (GFR > or =60 vs. <60 ml/min/1.73 m(2)) at entry or urine dipstick protein status prior to or during the period of treatment. These findings suggest that rosuvastatin may arrest the progression of renal disease.

Albuminuria and proteinuria in hospitalized patients as measured by quantitative and dipstick methods

We tested patients' urines for albumin, protein, and creatinine by quantitative and dipstick methods. The concentrations of these analytes were established by quantitative, cuvet-based chemistry methods that we assumed gave the "correct" values. There was good to excellent agreement of the dipstick results with the quantitative methods for the above three analytes. We found many patients who excreted pathological amounts of albumin and/or protein who did not have a diagnosis of kidney disease or other likely causes of proteinuria, suggesting that albuminuria and/or proteinuria were underdiagnosed in our group of patients. Those with cardiovascular disease, kidney disease, or diabetes showed the greatest predictive value of a positive test for albumin or protein by dipstick. Dipstick testing for albumin, protein, and creatinine had good or excellent agreement with quantitative methods. The dipstick tests were easy to use, simple, and low in cost, and can serve well for point-of-care testing.

Rapid diagnosis of infectious pleural effusions by use of reagent strips

Reagent strips have not yet been tested for use in the diagnosis of infectious pleural effusions. A reagent strip was used to evaluate 82 patients with pleural effusions: 20 patients had transudative effusions, 35 had infectious exudative effusions (empyema in 14 and parapneumonic effusion in 21), and 27 had noninfectious exudative effusions. Pleural fluid protein, as evaluated by the reagent strip, proved accurate for the detection of exudative effusions (sensitivity, 93.1%; specificity, 50%; positive predictive value, 84.3%; negative predictive value, 71.5%; odds ratio [OR], 6.77; and 95% confidence interval [CI], 1.87-24). The reagent strip leukocyte esterase test effectively detected infectious exudative effusions (sensitivity, 42.8%; specificity, 91.3%; positive predictive value, 88.2%; negative predictive value, 51.2%; OR, 4.46; and 95% CI, 1.2-16.4). Pleural pH was significantly predicted by the reagent strip but was of no assistance in categorization of exudative effusions as infectious or noninfectious. Compared with physical, laboratory, and microbiological data, the reagent strip was as accurate for estimation of percentages of infectious and noninfectious exudative effusions. Thus, reagent strips may be a rapid, easy-to-use, and inexpensive technique for discriminating transudative from exudative pleural effusions and for categorizing exudative pleural effusions as infectious or noninfectious.

Urinary protein and albumin excretion corrected by creatinine and specific gravity

Timed urine collections are difficult to use in clinical practice owing to inaccurate collections making calculations of the 24-h albumin or protein excretion questionable. One of our goals was to assess the 'correction' of urinary albumin and (or) protein excretion by dividing these by either the creatinine concentration or the term, (specific gravity-1)x100(1). The 24-h creatinine excretion can be estimated based on the patients' gender, age and weight. We studied the influence of physiological extremes of hydration and exercise, and protein and creatinine excretion in patients with or suspected kidney disorders. Specimens were collected from healthy volunteers every 4 h during one 24-h period. We assayed the collections individually to give us an assessment of the variability of the analytes with time, and then reassayed them after combining them to give a 24-h urine. For all volunteers, the mean intra-individual CVs based on the 4-h collections expressed in mg/24 h were 80.0% for albumin and 96.5% for total protein (P0.2). The CVs were reduced by dividing the albumin or protein concentration by the creatinine concentration or by the term, (SG-1)x100. This gave a CV for mg albumin/g creatinine of 52% (P<0.1 vs. albumin mg/g creatinine); mg protein/g creatinine of 39% (P<0.05 vs. mg protein/g creatinine); mg albumin/[(SG-1)x100] of 49% (P<0.1 vs. albumin)/[(SG-1)x100]; and mg protein/[(SG-1)x100] of 37% (P<0. 05 vs. mg protein)/[(SG-1)x100]. For the 68 subjects in the study, the strongest correlation was between the creatinine concentrations and the 24-h urine volume: r=0.786, P<0.001. The correlation of (SG-1)x100 vs. the 24-h urine volume was: r=0.606, P<0.001; for (SG-1)x100 and the creatinine concentration, the correlation was: r=0.666, P<0.001. Compared to the volunteers, the albumin and protein excretion in mg/24 h were more variable in the patients. The same was true if the albumin or protein concentrations were divided by the creatinine concentration or by (SG-1)x100. Protein and albumin concentrations were lower in dilute urines. Dividing the albumin or protein concentrations by the creatinine concentration reduced the number of false negative protein and albumin results. Dividing the albumin or protein values in mg/24 h by (SG-1)x100 eliminated fewer false negatives. Albumin concentrations increased significantly after vigorous exercise. The increase was almost eliminated when the albumin result was divided by the creatinine concentration suggesting that a decreased urine flow and not increased glomerular permeability causes an increase of post-exercise albuminuria. The same was true for proteinuria. A dipstick test plus an optical strip reader that can measure urine protein, albumin, and creatinine and calculate the appropriate ratios provides a better screening test for albuminuria or proteinuria than one measuring only albumin or protein.

High-sensitivity dye binding assay for albumin in urine

We developed a dye-binding method for albumin in urine based on bis (3',3"-diiodo4'4"-dihydroxy-5'5"-dinitrophenyl)-3,4,5,6-tetrabr omosulfonphthalein (DIDNTB), a dye that has a higher chemical sensitivity and specificity for albumin when compared to two other commonly used dyes. We prepared urine dipsticks with DIDNTB and certain other compounds to prevent "nonspecific" binding to the dipstick matrix. The detection limit for albumin with DIDNTB as the dye is about 10 mg/L. The extent of dye binding to proteins and other compounds was studied using ultracentrifugation and a selectively permeable membrane that permitted the passage of free but not bound dye; we believe this method is superior to photometric titration. The affinity of the dyes for albumin was found to be pH dependent with stronger binding at pH 1.8 than at pH 7.0. At pH 1.8, DIDNTB had a ca.10-fold greater binding coefficient to albumin when compared to the widely used dyes, tetrabromophenol blue (CI 4430-25-5) or bromophenol blue (CI 115-39-9). We developed a system that minimized nonspecific binding by the dye through the use of polymethyl vinyl ethers and bis-(heptapropylene glycol) carbonate. DIDNTB showed a greater chemical specificity for albumin when compared to most other proteins. The new albumin dipsticks are resistant to many potential interferences at substantial concentrations, making the dipsticks suitable to screen for albuminuria.

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.