Estimating urine albumin to creatinine ratio from protein to creatinine ratio using same day measurement: validation of equations.

OBJECTIVES: Severity of chronic kidney disease is defined by glomerular filtration rate (GFR) and albuminuria (ACR) by the KDIGO and are related to cardiovascular outcomes and end-stage-kidney-failure. However, proteinuria (PCR) is more often available than ACR in records. Recently, equations were developed to estimate ACR from PCR. We investigated their performances in our population. METHODS: In the academic medical hospital of Liège, we retrospectively analysed same day measurement of ACR and PCR and staged them according to the KDIGO A1-A2-A3 categories. Analyser Roche Cobas (R) gathered 2,633 urinalysis (May 2018-May 2019) and analyser Abbott Alinity (A) 2,386 urinalysis (May 2019-March 2020). We compared the KDIGO staging of mACR and eACR obtained from Weaver's and Sumida's equations. RESULTS: Median age was 63 [52;71]/64 [53;72] years old, 43/42% were female; 78/74% had diabetes; proportion of mACR-A1 was 65.6%/64.2%, A2 was 25.5%/25.5% and A3 was 8.8%/10.3% (Method R/A, respectively). Both equations gave similar distribution of KDIGO staging of eACR. Overall agreements were higher than 88% regardless of the analyser or of the equation. Performances in between equations were equivalent according to the multi-level AUC (multinomial logistic regression model). CONCLUSIONS: Good concordance was observed between mACR and eACR regardless of the equation or of the analyser. No patient with an A3-measured ACR was estimated within the KDIGO A1 category. Though ACR should be measured when clinically needed, it may be reasonably estimated from the PCR through these equations, for epidemiologic retrospective studies or research purposes.

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).

Proteinuria in COVID-19: prevalence, characterization and prognostic role.

BACKGROUND: Proteinuria has been commonly reported in patients with COVID-19. However, only dipstick tests have been frequently used thus far. Here, the quantification and characterization of proteinuria were investigated and their association with mortality was assessed. METHODS: This retrospective, observational, single center study included 153 patients, hospitalized with COVID-19 between March 28th and April 30th, 2020, in whom total proteinuria and urinary α1-microglobulin (a marker of tubular injury) were measured. Association with mortality was evaluated, with a follow-up until May 7th, 2020. RESULTS: According to the Kidney Disease Improving Global Outcomes staging, 14% (n = 21) of the patients had category 1 proteinuria (< 150 mg/g of urine creatinine), 42% (n = 64) had category 2 (between 150 and 500 mg/g) and 44% (n = 68) had category 3 proteinuria (over 500 mg/g). Urine α1-microglobulin concentration was higher than 15 mg/g in 89% of patients. After a median follow-up of 27 [14;30] days, the mortality rate reached 18%. Total proteinuria and urinary α1-microglobulin were associated with mortality in unadjusted and adjusted models. This association was stronger in subgroups of patients with normal renal function and without a urinary catheter. CONCLUSIONS: Proteinuria is frequent in patients with COVID-19. Its characterization suggests a tubular origin, with increased urinary α1-microglobulin. Tubular proteinuria was associated with mortality in COVID-19 in our restropective, observational study.

Urinary strips for proteins: easy to do but difficult to read!

Urine is an easily accessible biological fluid. This availability makes it tempting for a direct analysis of urinary parameters by physicians. Urinary proteins, that are interesting markers for several pathologies, are detected by urinary strips, rapidly and at a low cost. However, to ensure an optimal use of urinary strips, one may be familiar to their characteristics and their limits. This paper details the available urinary strips used for the detection of urinary proteins and urinary albumin, as well as their analytical performances in clinical conditions such as pregnancy, chronic renal disease, diabetes or for the screening of general populations.

Urinary protein or albumin/creatinin ratio for reporting measurements results.

Urinary proteins or urinary albumin exhibit a high intra individual variability. Therefore, urine collected during 24 hours has been recognized as a reference biological fluid for usual values determination. However, urine collection during a day is difficult and numerous studies have been performed to replace the "gold standard" with measures on random samples and results given as protein/creatinine ratio or albumin/creatinine ratio, to decrease the variability. The paper presents the populations where ratios are well correlated with protein excretion, the cut-off values recommended in clinical settings and the limits of using ratio rather than 24 h excretion.