Diagnostic accuracy of point-of-care tests for detecting albuminuria: a systematic review and meta-analysis.

BACKGROUND: Experts recommend screening for albuminuria in patients at risk for kidney disease. PURPOSE: To systematically review evidence about the diagnostic accuracy of point-of-care (POC) tests for detecting albuminuria in individuals for whom guidelines recommend such detection. DATA SOURCES: Cochrane Library, EMBASE, Medion database, MEDLINE, and Science Citation Index from 1963 through 5 December 2013; hand searches of other relevant journals; and reference lists. STUDY SELECTION: Cross-sectional studies, published in any language, that compared the accuracy of machine-read POC tests of urinary albumin-creatinine ratio with that of laboratory measurement. DATA EXTRACTION: Two independent reviewers extracted study data and assessed study quality using the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2) tool. DATA SYNTHESIS: Sixteen studies (n = 3356 patients) that evaluated semiquantitative or quantitative POC tests and used random urine samples collected in primary or secondary ambulatory care settings met inclusion criteria. Pooling results from a bivariate random-effects model gave sensitivity and specificity estimates of 76% (95% CI, 63% to 86%) and 93% (CI, 84% to 97%), respectively, for the semiquantitative test. Sensitivity and specificity estimates for the quantitative test were 96% (CI, 78% to 99%) and 98% (CI, 93% to 99%), respectively. The negative likelihood ratios for the semiquantitative and quantitative tests were 0.26 (CI, 0.16 to 0.40) and 0.04 (CI, 0.01 to 0.25), respectively. LIMITATION: Accuracy estimates were based on data from single-sample urine measurement, but guidelines require that diagnosis of albuminuria be based on at least 2 of 3 samples collected in a 6-month period. CONCLUSION: A negative semiquantitative POC test result does not rule out albuminuria, whereas quantitative POC testing meets required performance standards and can be used to rule out albuminuria. PRIMARY FUNDING SOURCE: None.

Investigation of apparent non-albuminuric proteinuria in a primary care population.

BACKGROUND: There is debate as to whether using the urinary albumin- or protein-to-creatinine ratio (ACR or PCR) should be the primary test for proteinuria. Whilst albuminuria (increased ACR) in the absence of proteinuria (increased PCR) may be expected in some patients, the converse (i.e., proteinuria in the absence of albuminuria) is more unusual and its cause and significance are unclear. We investigated the nature of such apparent non-albuminuric proteinuria in a primary care population of patients. METHODS: ACR and PCR were measured in 569 urine samples from patients who either had chronic kidney disease or were at increased risk of the condition. Samples with apparent proteinuria (PCR ≥23 mg/mmol/≥200 mg/g) but no albuminuria (ACR <3.4 mg/mmol/<30 mg/g) were classified as 'discrepant' (37% of proteinuric samples, 6% of all samples); 27 of these samples were available for further analyses. The further analyses included electrophoresis, repeat measurement, immunoassays for markers of tubular proteinuria and use of alternative albumin and total protein methods. RESULTS: Electrophoresis did not identify significant proteinuria in the discrepant samples. The only evidence of tubular proteinuria following measurement of three urinary markers of the condition was a mildly increased α1-microglobulin-to-creatinine ratio in 10 of the 27 discrepant samples analysed, four of which also had a raised ß-trace protein-to-creatinine ratio. Use of an alternative urinary total protein method resulted in significantly lower PCRs and 17 of the 27 samples were no longer classified as proteinuric. CONCLUSIONS: We were unable to confirm the cause of a raised PCR without albuminuria in these patients and suspect that in most cases it is artefactual.

The diagnostic accuracy of a urine albumin-creatinine ratio point-of-care test for detection of albuminuria in primary care.

BACKGROUND: Albuminuria is an important sign of chronic kidney disease and is detected routinely by measurement of urinary albumin-creatinine ratio (ACR). A Siemens CLINITEK test designed for use at the point of care is available that can semiquantitatively measure ACR. STUDY DESIGN: Diagnostic accuracy study evaluating a urinary ACR point-of-care test. SETTING & PARTICIPANTS: The semiquantitative ACR test was evaluated at the point of care in a representative primary care population (those with or at increased risk of chronic kidney disease) of 642 patients under standard operational conditions and compared with the reference standard of ACR measurement in the clinical laboratory. INDEX TEST: The point-of-care CLINITEK semiquantitative ACR test. This test uses dye-binding and catalytic assays for albumin and creatinine, respectively, on a Microalbumin 9 strip, which is read by the CLINITEK Status Analyzer, and ACR is calculated automatically. REFERENCE TEST: Laboratory measurement of albumin and creatinine on an Abbott Architect analyzer by immunoturbidimetric and enzymatic assays, respectively, and calculation of ACR. RESULTS: The prevalence of albuminuria (laboratory ACR≥30 mg/g) in the study population was 20.2%. Sensitivity and specificity of the point-of-care test for detecting albuminuria were 83.2% and 80.0%, respectively. Positive and negative predictive values were 51.2% and 95.0%, respectively; positive and negative likelihood ratios were 4.16 and 0.21, respectively. Twenty-three (3.6%) samples measured at the point of care were not analyzed in the central laboratory for a variety of reasons, including laboratory reception data entry errors. LIMITATIONS: Our sensitivity calculation is accurate to an approximately 8% CI. CONCLUSIONS: The instrument-read reagent strip test was a poor rule-in test for albuminuria at the point of care, as evidenced by the low positive predictive value, but was a reasonable rule-out test. Observed sensitivity was lower than reported in earlier laboratory-based studies. This decreased diagnostic accuracy needs to be balanced against the potential advantages of a point-of-care testing approach.

Protein and albumin-to-creatinine ratios in random urines accurately predict 24 h protein and albumin loss in patients with kidney disease.

BACKGROUND: Random urine protein-to-creatinine (PCR) and albumin-to-creatinine (ACR) ratios have been proposed as alternatives to 24 h urine measurements to simplify sample collection and overcome errors. The aim of this study was to examine the ability of PCR and ACR to predict urinary 24 h protein and albumin loss, respectively, in patients with kidney disease, and determine the most appropriate time of collection. METHODS: Eighty-three patients were recruited from a renal outpatient clinic. In a 24 h period, each collected an early-morning urine (EMU), second and third voids, and the remaining urine passed that day. PCR and ACR were determined in random urines and compared with the 24 h loss of protein and albumin, respectively. RESULTS: For all patients, median (range) 24 h urine protein and albumin losses were 220 (30-15600) and 60 (<8-10,557) mg, respectively. Ratios derived from each of three random urines correlated well with 24 h protein or albumin loss (Spearman's r(s) > 0.87, P < 0.0001). Receiver operator characteristic (ROC) curve analysis showed PCR accurately predicted both an abnormal 24 h urine protein > or =150 mg/24 h (areas under curves [AUC] 0.90-0.92) and significant proteinuria above 300 mg/24 h (AUC between 0.97 and 1.00). ACR accurately predicted both an abnormal 24 h urine albumin > or =30 mg/24 h (AUC 0.98 to 0.99) and frank albuminuria at > or =300 mg/24 h or > or =700 mg/24 h (AUC between 0.99 and 1.00). EMU and random urines performed equally well in predicting proteinuria and albuminuria from PCR and ACR, respectively. CONCLUSIONS: By careful choice of cut-offs, both PCR and ACR can be used in patients with kidney disease to rule in or rule out abnormal 24 h losses of protein and albumin. EMU and, importantly, random samples can be used as surrogates for 24 h urine collections.

Use of protein:creatinine ratio measurements on random urine samples for prediction of significant proteinuria: a systematic review.

BACKGROUND: Proteinuria is recognized as an independent risk factor for cardiovascular and renal disease and as a predictor of end organ damage. The reference test, a 24-h urine protein estimation, is known to be unreliable. A random urine protein:creatinine ratio has been shown to correlate with a 24-h estimation, but it is not clear whether it can be used to reliably predict the presence of significant proteinuria. METHODS: We performed a systematic review of the literature on measurement of the protein:creatinine ratio on a random urine compared with the respective 24-h protein excretion. Likelihood ratios were used to determine the ability of a random urine protein:creatinine ratio to predict the presence or absence of proteinuria. RESULTS: Data were extracted from 16 studies investigating proteinuria in several settings; patient groups studied were primarily those with preeclampsia or renal disease. Sensitivities and specificities for the tests ranged between 69% and 96% and 41% and 97%, respectively, whereas the positive and negative predictive values ranged between 46% and 95% and 45% and 98%, respectively. The positive likelihood ratios ranged between 1.8 and 16.5, and the negative likelihood ratios between 0.06 and 0.35. The cumulative negative likelihood ratio for 10 studies on proteinuria in preeclampsia was 0.14 (95% confidence interval, 0.09-0.24). CONCLUSION: The protein:creatinine ratio on a random urine specimen provides evidence to "rule out" the presence of significant proteinuria as defined by a 24-h urine excretion measurement.