Difference of urinary protein components and the correlation between urinary protein quantification and glomerular filtration rate in pregnant women with pre-eclampsia

Abstract

Objective: To investigate the difference of urinary protein components in pregnant women with pre-eclampsia (PE) with different degrees of proteinuria and the correlation between 24-hour urinary protein quantification and estimated glomerular filtration rate (eGFR). Methods: Clinical data of 101 PE pregnant women who were delivered in Renji Hospital, Shanghai Jiao Tong University School of Medicine from July 2018 to June 2022 were retrospectively analyzed. According to 24-hour urinary protein quantification, they were divided into 3 groups, including 40 cases of mild proteinuria group (24-hour urinary protein quantification ≤2.0 g), 21 cases of moderate proteinuria group (2.0 g<24-hour urinary protein quantification ≤5.0 g), 40 cases of severe proteinuria group (24-hour urinary protein quantification >5.0 g). The general clinical data, urinary protein index and renal function index of PE pregnant women in 3 groups were compared. The eGFR was calculated based on age, serum creatinine (sCr), blood urea nitrogen (BUN) and serum albumin (sAlb). Correlation analysis was conducted between 24-hour urinary protein quantification and each index of eGFR. Results: (1) General clinical data: the median PE onset week (31 weeks) and delivery gestational week [(36.4±3.6) weeks] of PE pregnant women in the mild proteinuria group were later than those in the moderate proteinuria group [median PE onset: 22 weeks, delivery: (32.2±4.2) weeks] and severe proteinuria group [median PE onset: 25 weeks, delivery: (29.6±3.4) weeks]; systolic blood pressure, diastolic blood pressure, alanine aminotransferase, aspartate aminotransferase levels and the incidence of fetal growth restriction were lower than those in the moderate and severe proteinuria groups; median newborn birth weight (3 150 g) was higher than those in the moderate proteinuria group (1 305 g) and the severe proteinuria group (1 042 g), respectively. The differences were statistically significant (all P<0.05). (2) Urinary protein index: the 24-hour urinary protein quantification, urinary microalbumin (mAlb) and urinary transferrin (TRF) levels of PE pregnant women in the mild proteinuria group, moderate proteinuria group and severe proteinuria group were increased successively, and the differences were statistically significant (all P<0.05). The median urinary α1-microglobulin (α1-MG) level of PE pregnant women in the severe proteinuria group (50 mg/L) was significantly higher than those in the mild proteinuria group (17 mg/L) and moderate proteinuria group (22 mg/L; all P<0.05), but there was no significant difference between the mild proteinuria group and the moderate proteinuria group (P>0.05). There was no significant difference in the median urinary β2-microglobulin (β2-MG) level among the 3 groups (P=0.632). (3) Renal function index: sAlb and eGFR of PE pregnant women in the mild proteinuria group, moderate proteinuria group and severe proteinuria group were successively decreased, and BUN was successively increased, respectively, and the differences were statistically significant (all P<0.05). The sCr level of PE pregnant women in the severe proteinuria group was significantly higher than those in the mild proteinuria group and the moderate proteinuria group (all P<0.05), but there was no significant difference between the mild proteinuria group and the moderate proteinuria group (P>0.05). (4) Correlation analysis: the 24-hour urinary protein quantification of PE pregnant women was significantly negatively correlated with eGFR (r=-0.645, P<0.001), and was correlated with the variables sAlb (r=-0.549, P<0.001), sCr (r=0.582, P<0.001) and BUN (r=-0.657, P<0.001) in the eGFR calculation formula. The 24-hour urinary protein quantification were significantly negatively correlated with the gestational weeks of PE onset, gestational weeks of termination of pregnancy and newborn birth weight (all P<0.05). Conclusions: The protein composition in the urine of PE pregnant women with different degrees of proteinuria is not different, but the protein level is significantly different. There is a significant negative correlation between the increase of 24-hour urinary protein quantification and the decrease of eGFR.