Serum cystatin C is independently associated with renal impairment and high sensitivity C-reactive protein in systemic lupus erythematosus.

OBJECTIVES:
In systemic lupus erythematosus (SLE) patients, glomerular filtration rate (GFR) is usually estimated using the modified Cockcroft-Gault (mCG) and Modification of Diet in Renal Disease (MDRD) equations. We aimed to study cystatin C (sCysC) in SLE to assess its agreement with standard renal indices and investigate factors affecting sCysC in SLE.

METHODS:
SLE patients (≥4 ACR criteria) and healthy women from Greater Manchester were recruited and clinical assessments were undertaken. SCysC was measured using R & D Systems` ELISA. Agreement between renal measures was assessed using Deming plots and factors associated with sCysC in SLE were examined by multiple linear regression analyses.

RESULTS:
178 patients and 68 controls had median (IQR) ages of 53 (46–61) and 50 (39–60) years, respectively. In an age-adjusted analysis, SLE patients had higher sCysC (1.16 [0.98–1.36] vs. 0.950 [0.73–1.13] mg/l; p<0.0001) and within SLE those with a history of lupus nephritis had higher sCysC (1.31 [1.10–1.66] vs. 1.11 [0.95–1.29] mg/l; p<0.005). SCysC correlated positively with serum creatinine, and inversely to renal measures (r=-0.530; p<0.0001 [mCG], and r=-0.620; p<0.0001 [MDRD]). There was closer agreement between the two eGFR measures than between either eGFR measures and sCysC. In addition to age and serum creatinine, a multivariate analysis (β, p) found that high-sensitivity C-reactive protein (hs-CRP) (0.03, 0.026) was also independently associated with sCysC in SLE.

CONCLUSIONS:
In SLE, sCysC may be influenced by low grade inflammation as well as by renal dysfunction. Therefore, SCysC should not supplant current assessment of renal dysfunction in SLE.