Non-GFR determinants of creatinine and cystatin C
| Increase serum creatinine concentration |
| Muscle mass |
| Protein intake |
| Rhabdomyolysis |
| Increase serum cystatin C |
| Male |
| Older age |
| Obesity |
| Smoking |
| Hyperthyroidism (hypothyroidism decreases it) |
| Glucocorticoid therapy |
| Inflammatory markers (C-reactive protein) |
| Malignancy |
| Consider ordering serum cystatin C GFR |
| In patients at the extremes of muscle mass or cachexia |
| When the serum creatinine concentration is elevated without urinary or radiologic evidence of kidney damage |
| When a more precise GFR measurement will change treatment decisions |
GFR = glomerular filtration rate