IMPACT OF THYROID DYSFUNCTION ON SERUM CYSTATIN C AS A NOVEL ENDOGENOUS MARKER OF RENAL FUNCTION COMPARED WITH CREATININE CLEARANCE

Serum cystatin C is a novel marker for kidney function. The impact of thyroid dysfunction on serum concentrations of some renal markers such as cystatin C, β2-microglobulin and creatinine along with creatinine clearance (Ccr) (golden standard parameter) was investigated throughout a randomized prospective study to evaluate the changes which might be produced in serum cystatin C compared with serum concentrations of creatinine and β2-microglobulin when used as renal markers in thyroid patients. Subjects were classified into four groups: first group included 30 healthy person, group (II) included 30 kidney dysfunction patients who were at risk for developing chronic renal failure, group (III) included 30 patients of the hypothyroid states before and after treatment and group (IV) included 30 hyperthyroid patients before and after treatment. In kidney dysfunction group, a decline in Ccr was observed and associated with a significant increase in the levels of serum cystatin C (6.52±0.93), creatinine (3.1±0.7) and β2-microglobulin (2.66±0.81) when compared with the healthy control subjects. A highly significant correlation was found between Ccr and cystatin (r= 0.767, p 0.001) than that found with creatinine (r= 0.514, p 0.05) and 02-microglobulin (r= 0.476, p 0.05) in the kidney dysfunction group explaining the use of cystatin C as a sensitive endogenous marker of renal function and probably superior alternative to creatinine clearance, serum creatinine and serum β2-microglobulin when used to assess renal function. The obtained data within groups (III) and (IV) showed that there was an inverse relationship between both free thyroxine (FT4) and free triiodothyronine (FT3) with creatinine but a direct relationship was found with cystatin C and in both cases Ccr remained normal. β2-microglobulin was significantly increased in both cases of hypo- and hyperthyroid states so that it is not a good marker for kidney function in those patients. In conclusion, serum cystatin C was considered a sensitive marker for renal function when compared with other parameters but thyroid dysfunction should be taken in consideration to exclude thyroid dysfunction effects upon cystatin C. Also, estimated creatinine clearance remained a better estimate of glomerular filtration rate for the kidney than does cystatin C if thyroid dysfunction is suspected and in this case we recommend to determine cystatin C together with TSH and FT4 to exclude thyroid disorders.