Background: Serum creatinine is not a satisfactory marker of glomerular
filtration rate (GFR) in patients with spinal cord injury (SCI) who have varying
degrees of muscle atrophy. In contrast to serum creatinine, serum cystatin C, a
13-kDa protein, is not affected by muscle mass and is therefore potentially a useful
marker of GFR in patients with SCI. In addition, cystatin C is not dependent on sex
or age and is not secreted by the renal tubule.
Aim: We assessed serum cystatin C as a surrogate marker of GFR in SCI
patients.
Methods: Cystatin C was analysed using a particle-enhanced
immunonephelometric assay (Dade Behring) in serum samples sent for routine
measurement of creatinine (64 patients) and creatinine clearance (27 patients) from
patients in the Spinal Unit of the Austin Health. We compared these results with
serum cystatin C of 57 non-SCI patients who had had a creatinine clearance
measurement during the study period.
Results: In patients with SCI, the reciprocal of cystatin C had a
stronger correlation (r = 0·48, P<0·01) with creatinine clearance than the
reciprocal of serum creatinine (r = 0·25, P<0·19). Further, the value of serum
creatinine was much lower for a given creatinine clearance in SCI patients than in
non-SCI patients; the serum cystatin C concentrations were equivalent.
Conclusion: The serum cystatin C is a convenient and more reliable
surrogate marker of GFR than serum creatinine and will enable early detection of
renal impairment. We need to confirm this finding with a larger study, including
comparison with an accepted gold standard for GFR.
