The correlation analysis between renal artery resistance index and renal function in patients with thrombotic microangiopathy

Abstract

Objective To explore the correlations between renal artery resistance index(RRI)and renal function in patients with thrombotic microangiopathy (TMA)so as to provide the clinical basis for predictable diagnosis and treatment in patients with acute kidney injury(AKI). Methods Patients diagnosed with thrombotic microangiopathy admitted to department of emergency of Peking Union Medical College Hospital between August 1st, 2014 and March 31th, 2015 were enrolled. Intrarenal arteries resistive index of right kidney was detected in all cases on admission by color Doppler flow image. The serum creatinine(SCR) and glomerular filtration rate(GFR)were measured at the same time. According to the diagnostic criteria of the guideline ofKidney Disease: Improving Global Outcomes 2012(KDIGO-AKI 2012), patients were divided into non-AKI group and AKI group. The intergroup difference was compared and the correlation between RRI and SCR as well as between RRI and GFR were assessed. RRI, SCR and GFR were measured again at the most severe stage of kidney injury. The above index were marked as RRI*, SCRmax and GFRmin. At the same time, ΔRRI(RRI*-RRI), ΔSCR(SCRmax-SCR)and ΔGFR(GFR-GFRmin)were calculated. According to the stage classification of KDIGO-AKI 2012, 36 patients diagnosed with AKI during their hospitalization were divided into KDIGO-1 group(n=10), KDIGO-2 group(n=10) or KDIGO-3 group(n=16). The intergroup difference of RRI* was compared and the correlation between ΔRRI and ΔSCR as well as between ΔRRI and ΔGFR were assessed. Results When RRI>0.7 was used as the diagnostic threshold for AKI, the sensitivity was 92.3% and the specificity was 80.1%. RRI was positively correlated with SCR(r1=-0.728, P<0.01; r2=-0.709, P<0.01)and negatively correlated with GFR(r1=-0.728, P<0.01; r2=-0.709, P<0.01)in all patients at the time of admission and the most severe stage of kidney injury. While there was a significant difference in the RRI* among KDIGO-1, KDIGO-2 and KDIGO-3 groups(F=37.979, P=0.001), and there was no significant difference in ΔRRI (F=0.634, P=0.537). The ΔRRI was not correlated with ΔGFR or ΔSCR. Conclusions RRI can be used as a marker for diagnosis of AKI and the evaluation of renal function in patients with TMA, but it is not helpful to reflect the trends of renal injury especially for the critically ill patients. Key words: Thrombotic microangiopathy; Renal resistive index; Acute kidney injury; Diagnosis; Correlation