Background: The estimation of the glomerular filtration rate (GFR) is an important part of the clinical evaluation of renal function. In clinical practice serum creatinine and creatinine clearance are the most commonly used methods for estimating GFR, but their use as a markers of GFR is connected with several problems. Cystatin C is a basic protein produced by nucleated cells. The low molecular mass and the basic nature of cystatin C, in combination with its stable production rate, suggested that the glomerular filtration rate (GFR) is the major determinant of cystatine C concentration in the peripheral circulation.
Objectives: The aim of the study was to evaluate serum cystatin C as a new marker of the glomerular filtration rate (GFR) in children with various renal diseases in comparison with serum creatinine and β2-microglobulin the most commonly used markers of the GFR.
Methods: Fifty subjects were included in this study and were divided into a control group and a patient group. The control group comprised 20 healthy infants and children with normal renal functions. The patients group comprised 30 patients with various renal diseases. The two groups were subjected to full clinical history, through clinical examination, routine investigations to confirm the etiology of renal diseases, kidney function tests (serum urea and creatinine levels), serum β2-microglobulin level, isotope renogram using 99 m TC-DTPA-clearance (for measuring GFR) and estimation of serum cystatin C level by particle-enhanced turbidimetric assay.
Results: The levels of serum creatinine, β2-microglobulin and serum cystatin C were significantly higher with the reduction of GFR in patients than control group. There was highly significant negative correlation of GRF with serum creatinine, serum β2-microglobulin and serum cystatin C (r = -0.69, -0.71, -0.89 respectively) and a highly significant positive correlation between serum cystatin C and both of serum creatinine and serum β2-microglobulin(r = 0.81, 0.67 respectively). Serum creatinine showed significant positive correlation with age and body mass index but no significant correlation with gender of Patients, while no correlation was found between serum cystatin C and serum β2-microglobulin and age, gender and body mass index. This study showed that serum cystatin C was more sensitive and specific (90.9% and 88.8% respectively) than serum creatinine (54.5% 75% respectively) and serum β2-microglobulin (86.7%, 75% respectively) as markers of GFR. Serum cystatine C level started to increase to greater than normal values when GFR value was (90 ml/min/1.73 m²), while serum β2-microglobulin and serum creatinine levels began to increase when GFR value was (80.1ml/min/1.73 m² and 76.7 ml/min/1.73 m² respectively).
Conclusions: These data suggest that measurements of serum cystatin C is superior to serum creatinine and serum β2-microglobulin to detected mild reduction of GFR in children, and therefore may be important in the detection of early renal insufficiency in a variety of renal diseases for which early treatment is critical.