Clinical Significance of Serum Cystatin C in SLE: A Potential Marker of Disease Damage Beyond Lupus Nephritis

Abstract

Objective: This work aimed to assess the serum level of cystatin C in systemic lupus erythematosus (SLE) patients and to determine the relation to disease characteristics and damage.   Methods: The study included 33 SLE patients presenting to the Internal Medicine and Rheumatology Department and Outpatient clinic, King Abdulaziz University, Saudi Arabia. The medical history, clinical examination, laboratory investigations and medications received by the patients were recorded. The systemic lupus international collaborating clinics damage index (SLICC-DI) was assessed. Serum cystatin C was measured using the immune-nephelometric method.   Results: The mean age of the patients was 35.3±10.7 years; 28 females and 5 males (F:M  5.6:1), disease duration 5.5±3.1 years and their age at onset was 27.9±10.6 years. Serum cystatin C level was significantly higher in patients with lupus nephritis (LN) (2.47±1.57 mg/L vs v mg/L, p=0.003) and diabetes (4.92±0.05 mg/L vs 1.93±1.34 mg/L; p<0.0001) and was lower in those with thyroid dysfunction (1.41±0.75 mg/L vs 2.3±1.59 mg/L, p=0.047). There was a significant correlation between the serum cystatin C level with proteinuria (r=0.57, p=0.011) and with the SLICC-DI (r=0.42,p=0.016). Serum cystatin C could discriminate patients with LN at cut-off value of 0.904 mg/L with area under the curve of 0.765, sensitivity 87% and specificity 50%; p=0.017.   Conclusion: The remarkable association between cystatin C and LN is confirmed and an emerging role is noted in reflecting the extent of disease damage. The likely association with diabetes and thyroid dysfunction should also be taken into consideration when deciding treatment regimens for LN patients.