Table 1.

Comparison of creatinine, Cystatin C, and β-trace protein as GFR markers

CreatinineCystatine Cβ-Trace Protein
Weight113 Da13,000 Da23,000–29,000 Da depending on the degree of glycosylation
StructureAmino acid derivativeNonglycosylated basic proteinGlycosylated protein
SynthesisMuscle mass, age, sex, diet, and pathologic factors can affect the circulating concentration of creatinine; lower in the elderly, women, and white peopleConstant by all nucleated cellsCerebrospinal fluid, brain, retina, melanocytes, heart, endothelial cells, and male genital organs; it is secreted into various body fluids, such as cerebrospinal fluid, plasma, seminal plasma, and urine
Presence in the serumIncreases at reduced GFRIncreases at reduced GFRIncreases at reduced GFR
AccuracySerum creatinine is increased only after a 50% reduction in GFRVery accurateVery accurate
Assay methodColorimetric and enzymatic assaysImmunonephelometric assayImmunonephelometric assay
Assay precisionVery good except in the presence of mild renal impairmentPrecise throughout the rangePrecise throughout the range
AdvantagesInexpensive and well characterizedMore precise and accurate than creatinineMore precise and accurate than creatinine
LimitationsNot only filtered at the glomerulus, but it is also excreted in the tubules; low precision at low renal impairmentAffected by C-reactive protein levels and thyroid function, not precise in the third trimester of pregnancy, and higher levels in tumor progression and metastasis; corticosteroid treatment falsely increases Cystatine C levels;Higher levels in meningiomas and hemangiopericytomas