Cystatin C deficiency is associated with the progression of small abdominal aortic aneurysms

Background: The cysteine protease inhibitor cystatin C may play a role in t he development and progression of abdominal aortic aneurysms (AA-As). Methods: From a mass screening trial of men aged 65-73 years, 151 small AAA s were followed for a mean of 2.9 years. Of these patients, 142 had serum s amples taken to determine the levels of cystatin C, creatinine and C-reacti ve protein (CRP). Results: Serum cystatin C concentration correlated negatively with AAA size (r = -0.22 (95 per cent confidence interval (c.i.) -0.59 to -0.02)) and an nual expansion rate (r = -0.24 (95 per cent c.i. -0.75 to -0.05)), persisti ng after adjustment for renal function, smoking, diastolic blood pressure, CRP, age and AAA size. Creatinine clearance and CRP did not correlate with size or expansion rate. Thirty-one AAAs had expanded to over 50 mm, when op eration was recommended. The serum level of cystatin C was a significant pr edictor of this occurrence, with a sensitivity and specificity of 61 and 57 per cent respectively. However, initial AAA size had the optimal sensitivi ty and specificity (both 81 per cent) in this regard. Conclusion: Deficiency of cystatin C was associated with increased aneurysm size and expansion rate, possibly due to lack of inhibition of cysteine pr oteases.