Hypertension and Afro-descendant ethnicity: a bad interaction for lupus nephritis treated with cyclophosphamide?

Hypertension and ethnicity are important prognostic factors in evolution of lupus nephritis. A cohort of 75 patients with lupus nephritis treated with cyclophosphamide was conducted to investigate the evolution of creatinine levels between Caucasians and Afro-descendants. A multiple linear model was used to evaluate the combined effects of ethnicity and hypertension over delta creatinine controlling confounders. Sample characteristics were: 85% females; mean (+/-SD) age of 33.6 +/- 12.0 years; 77% Caucasians; 40% hypertensive at renal biopsy; 91% WHO class IV; mean basal creatinine: 1.5 +/- 1.3 mg/dL; mean final creatinine: 2.1 +/- 2.5 mg/dL; 40% anaemia; proteinuria: 5.4 +/- 4.8 g/day. Comparing Caucasians and Afro-descendants, it was found: 28.1% versus 72.2% for hypertension (P = 0.002); 31.6% versus 66.7% for anaemia (P = 0.018); 5.9 +/- 5.0 versus 3.8 +/- 4.0. g/day (P = 0.02) for proteinuria. Other comparisons including basal creatinine did not reach statistical significance. Comparing outcomes between Caucasians and Afro-descendants, it was found: 10.5% versus 22.2% for doubling of creatinine (P = 0.24); 0.41 +/- 2.03 versus 1.05 +/- 2.41 for delta creatinine ( P = 0.29); 8.8% versus 22.2% for haemodialysis (P = 0.21) and 3.5% versus 5.6% for death (P = 0.99). Analysing delta creatinine with multiple linear regression showed that hypertension had a significant overall effect (b = 0.80; SE = 0.32; P = 0.015), ethnicity alone was not significant (b = 0.35; SE = 0.29; P = 0.228); however, the effect of hypertension on delta creatinine was more intense among Afro-descendants than among Caucasians (interaction term b = - 0.83; SE = 0.37; P = 0.027). Afro-descendants lupus patients experience worst prognosis of renal function probably due to the effect of hypertension and not ethnicity per se.