Markers for direct measurement are very accurate but cumbersome to use on a routine basis. As such, they are generally employed only in situations where other estimates of GFR are inadequate.
Patients in whom direct measurement may be beneficial over routine estimation include (Clarke, 2016):
- Those that are very young or old
- Those that are malnourished, obese, or vegetarian/vegan
- Those with a disease that affects skeletal muscle
Other situations include patients being evaluated for kidney donation or missing large portions of muscle mass (e.g., paraplegia).
