Which Is a Better Predictor of GFR Decline: 24-h Urine Protein or 24-h Protein-Creatinine Ratio? An Exploration of the MDRD Study Data

Background

Proteinuria is a known risk factor for progression of chronic kidney disease. Proteinuria magnitude can be estimated by measuring spot urine protein-to-creatinine ratio (least accurate), 24-h urine collection for protein (24 P), or 24-h protein-creatinine ratio (24 PCR). The MDRD study found that 24 P measured at baseline was the strongest single predictor of the rate of GFR decline during study follow-up. However, predictive powers of 24 P and 24 PCR have not been compared in the literature. The current study addresses this question using the MDRD cohort data.

Methods

The study is a retrospective analysis of prospectively collected data from the MDRD cohort using simple and multiple regression models. Slope of measured GFR (mGFR) over time was used as the response and models that included baseline 24 PCR or 24 P were compared for the entire sample and for subgroups formed by restricting the values of 24-h creatinine and 24 P.

Results

Log 24 P and Log 24 PCR correlated almost equally with mGFR slope. However, in simple linear regression models and multivariable linear regression models adjusting for age and sex, the model with 24 PCR had a higher R 2 than the corresponding one that had 24 P except for the subgroup 24 P < 1 g.

Conclusion

We observe that 24 PCR may be a better marker of proteinuria magnitude in predicting decline in kidney function compared to 24 P in particular for patients with 24 P ≥ 1. This finding needs validation in prospective clinical trials.

Soluble Urokinase-Type Plasminogen Activator Receptor, Changes of 24-Hour Blood Pressure, and Progression of Chronic Kidney Disease

Background

Soluble urokinase‐type plasminogen activator receptor (suPAR) is associated with cardiovascular risks and poor renal outcomes. However, whether elevated suPAR levels are associated with 24‐hour blood pressure patterns or kidney disease progression in patients with chronic kidney disease (CKD) is unclear.

Methods and Results

A total of 751 patients with CKD stage 1 to 5 were recruited from CMERC‐HI (Cardiovascular and Metabolic Disease Etiology Research Center–High Risk) cohort study (2013–2018). The relationship of serum suPAR levels to 24‐hour blood pressure parameters and CKD progression was analyzed. The median serum suPAR level was 1439.0 (interquartile range, 1026.2–2150.1) pg/mL, and the mean estimated glomerular filtration rate was 52.8±28.5 mL/min per 1.73 m² at baseline. Patients with higher suPAR levels had significantly higher levels of office, 24‐hour, daytime, and nighttime systolic blood pressure and nighttime diastolic blood pressure than those with lower suPAR levels. The highest suPAR tertile was associated with an increased risk of a reverse dipping pattern (odds ratio, 2.93; 95% CI, 1.27–6.76; P=0.01). During a follow‐up of 43.2 (interquartile range, 27.0–55.6) months, the CKD progression occurred in 271 (36.1%) patients. The highest suPAR tertile was significantly associated with higher risk of CKD progression than the lowest tertile (hazard ratio [HR], 2.09; 95% CI, 1.37–3.21; P=0.001). When the relationship was reevaluated with respect to each dipping pattern (dipper, extreme dipper, nondipper, and reverse dipper), this association was consistent only in reverse dippers in whom the risk of CKD progression increased (HR, 1.43; 95% CI, 1.02–2.01; P=0.03) with every 1‐unit increase in serum suPAR levels.

Conclusions

Elevated suPAR levels are independently associated with CKD progression, and this association is prominent in reverse dippers.