A recent brief in Nature Reviews Nephrology describes a study by Vart Scholars at the University Medical Center Groningen in the Netherlands on AJKD focusing on urinary albumin to creatinine ratio (ACR) and 24-hour urinary albumin excretion (24 h UAE) in the staging of proteinuria in chronic kidney disease (CKD). Increased urinary protein as a valuable risk marker for renal and cardiovascular (CV) complications has a number of methods to assess it. For a long time, 24-h UAE measurement was considered the gold standard for proteinuria assessment. However, the KDIGO 2012 edition guidelines state that ACR is superior to 24 h UAE for the assessment of proteinuria and recommend the use of ACR of morning urine as an assessment method. However, opponents argue that individuals with an elevated ACR may not have an elevated 24 h UAE. There are three main contradictions between ACR and 24 h UAE in urine protein staging: 1. It is possible that the increase in ACR is not due to an increase in urine protein, but rather to a decrease in urine creatinine concentration because creatinine, a product of muscle catabolism, is related to factors such as muscle mass, age and gender. 2, Proteinuria has a circadian rhythm and the assessment of ACR uses morning urine, which may differ from 24 h urine. 3, 24 h UAE is subject to urine collection errors. To assess the importance of classification errors when using morning urine ACR instead of 24 h UAE to assess proteinuria, Priya Vart et al. from the University Medical Center Groningen, The Netherlands, reassessed the classification of 7683 respondents in the PREVEND and RENAAL studies. When morning urine ACR was used instead of 24 h UAE assessment, 88% of the respondents were classified accordingly, only 4% were classified as high protein urinary excretion and 7.9% were classified as low protein urinary excretion. These patients reclassified as high ACR had an increased risk of cardiovascular morbidity and mortality compared to those who did not receive reclassification. In conclusion, there was a high concordance between early morning random urine ACR and 24 h UAE classification results. The number of individuals reclassified is limited, but when present, it also usually indicates a higher CV risk. Therefore, the authors’ study supports the recommendation of the KDIGO guidelines: use of morning urine or random urine ACR for CKD staging.