Impact of Mild Renal Impairment on the Relationship Between Blood Pressure and Renal Fractional Excretion of Albumin in Primary Hypertension

BACKGROUND: In a prospective, cross-sectional study design, the impact of reduced renal function on the relationship between blood pressure and renal fractional excretion of albumin (FEalb; an index of albumin leak by the entire nephron) was investigated in primary hypertension. METHODS: By estimated glomerular filtration rate (eGFR), 217 untreated primary hypertensives were stratified into 94 subjects with normal GFR having eGFR ≥ 90 mL/min/1.73 m2 and 123 subjects with mildly impaired GFR having 60 ≤ eGFR < 90 mL/min/1.73 m2. Blood pressure monitoring and urinary sampling were performed simultaneously over a 24-h period. RESULTS: Although systolic and diastolic blood pressures did not differ significantly between the mildly impaired GFR group and the normal GFR group (143 ± 15 vs. 141 ± 15 mmHg and 89 ± 9 vs. 88 ± 12 mmHg, P = 0.456 and 0.231), log FEalb was significantly greater in the mildly impaired GFR group than in the normal GFR group (3.04 ± 1.07 × 10-7 vs. 2.72 ± 0.82 × 10-7 %, P = 0.049). Systolic blood pressure was independently associated with log FEalb in both groups, but the slope of the relationship was greater in the mildly impaired GFR group than in the normal GFR group (ANCOVA: P = 0.029). This impact of renal impairment on the relationship was confirmed by the finding that the group × systolic blood pressure interaction was significantly associated with log FEalb in all subjects (partial r = -0.149, P = 0.029). CONCLUSIONS: Our data indicate that renal impairment, even if its degree is mild, could enhance the influence of co-existent hypertension on albumin leak by the entire nephron in primary hypertension.