From the Guidelines
Inulin clearance and PAH clearance are used to estimate glomerular filtration rate (GFR) and renal plasma flow (RPF), respectively, providing valuable insights into kidney function. These tests are considered the gold standard for measuring kidney function, as they offer more accurate measurements than routine clinical tests like creatinine clearance 1. Inulin clearance measures GFR, which represents how efficiently the kidneys filter blood through their glomeruli, while PAH clearance estimates RPF, indicating the volume of blood plasma flowing through the kidneys per unit time.
Key aspects of inulin and PAH clearance:
- Inulin is ideal for GFR measurement because it's freely filtered at the glomerulus without being secreted, reabsorbed, or metabolized by the kidneys.
- PAH is almost completely extracted from blood during a single pass through the kidneys, making it suitable for RPF estimation.
- These measurements help clinicians assess overall kidney function, diagnose kidney diseases, evaluate disease progression, and monitor treatment effectiveness.
Limitations and alternatives:
- While inulin and PAH clearance tests are highly accurate, they're typically reserved for research settings or specialized clinical situations due to their complexity and invasive nature.
- Estimated GFR calculations, such as those using plasma iohexol clearance, are more common in everyday practice, as they are less invasive and more convenient 1.
- The European Kidney Function Consortium (EKFC) has established an international consensus initiative to standardize plasma iohexol clearance as a method for measuring GFR, which may become a more widely used alternative to inulin and PAH clearance in the future 1.
From the Research
Inulin Clearance and PAH Clearance
Inulin clearance and PAH (para-aminohippuric acid) clearance are used to estimate glomerular filtration rate (GFR) and renal plasma flow (RPF), respectively.
- Inulin clearance is considered the gold standard for measuring GFR, as it is freely filtered by the glomeruli and neither reabsorbed nor secreted by the renal tubules 2.
- PAH clearance, on the other hand, is used to estimate RPF, as PAH is almost completely secreted by the renal tubules 2.
Estimation of Renal Function
These clearance tests are used to estimate renal function, which is essential for diagnosing and managing kidney disease.
- Inulin clearance is used to determine 'true' GFR in healthy adults, and its results are compared with other clearance techniques and prediction equations 3.
- PAH clearance is used to measure effective renal plasma flow (ERPF), which is an important parameter in evaluating renal function 4.
Advantages and Limitations
The advantages of using inulin and PAH clearance include:
- Accurate measurement of GFR and RPF 2.
- No need for urine collection, making the procedure less invasive and easier to perform 5. However, there are also some limitations, such as:
- The need for continuous intravenous infusion and blood sampling 2.
- The potential for errors in measurement and calculation 6.
Clinical Applications
Inulin clearance and PAH clearance have several clinical applications, including: