CST3 and chronic kidney disease: Considering the fact that at these stages of CKD there exists a high correlation between proteinuria and 99mTc-DTPA scyntigraphy, and higher correlations between proteinuria and cystatin C-related equations when compared to creatinine-based ones, a tempting hypothesis to explain this situation is that 99mTc-DTPA and cystatin C themselves are only filtered by the glomerulus.