How can Renal Plasma Flow (RPF) be measured?

From the Guidelines

Renal plasma flow can be accurately measured using the iohexol plasma clearance method, which is a standardized and widely available technique. This method involves administering iohexol, a non-radioactive contrast agent, and then collecting plasma samples to measure its clearance, which reflects renal plasma flow 1. The iohexol plasma clearance method is based on pharmacokinetic models that assume one or two compartments of distribution of the exogenous marker in the human body. The European Kidney Function Consortium (EKFC) has established an international consensus initiative to standardize iohexol plasma clearance as a method for measuring renal plasma flow, making it a reliable and accessible technique for clinical use 1.

Some of the key advantages of the iohexol plasma clearance method include:

• It does not require a timed urine sample collection, making it easier to perform in outpatient settings
• It is not impacted by urinary retention, which can affect the accuracy of other measurement methods
• Plasma samples can be collected and stored frozen for later analysis, allowing for greater flexibility in testing
• The method is based on widely available and non-radioactive materials, making it safer and more accessible than other techniques

The iohexol plasma clearance method has been validated against other measurement techniques, such as urinary clearance methods, and has been shown to provide accurate and reliable results 1. As such, it is a valuable tool for assessing kidney function and monitoring disease progression in patients with suspected renal disease.

In comparison to other methods, such as the para-aminohippuric acid (PAH) clearance method, the iohexol plasma clearance method offers several advantages, including greater ease of use and wider availability 1. While PAH clearance is considered the gold standard technique, it requires intravenous administration of PAH and timed urine collections, which can be more cumbersome and less accessible than the iohexol plasma clearance method.

Overall, the iohexol plasma clearance method is a reliable and accessible technique for measuring renal plasma flow, and its standardization by the EKFC has made it a valuable tool for clinical use 1.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Measurement of Renal Plasma Flow

Renal plasma flow can be measured using various methods, including:

• Para-aminohippuric acid (PAH) clearance, which is considered the gold standard for estimating effective renal plasma flow 2, 3, 4, 5
• PAH clearance can be measured using a microplate-based assay 2 or high-performance liquid chromatography (HPLC) 2, 4
• Iothalamate clearance can also be used to estimate glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) 4
• Magnetic resonance imaging with arterial spin labeling (MRI-ASL) is a non-invasive approach to measure kidney perfusion and can be used to approximate kidney perfusion and changes in kidney perfusion due to pharmacological intervention 6
• Conventional methods such as continuous intravenous infusion with blood and urine sample collections can also be used to measure PAH clearance 5

Advantages and Limitations of Each Method

• PAH clearance using microplate-based assay is a rapid, precise, and accurate method, but may not be as widely available as other methods 2
• HPLC method is a reference method for PAH assay, but may be more expensive and time-consuming than microplate-based assay 2
• MRI-ASL is a non-invasive method, but may not be as accurate as other methods and requires specialized equipment 6
• Conventional methods such as continuous intravenous infusion with blood and urine sample collections are considered gold standard, but may be more invasive and time-consuming than other methods 5

Comparison of Methods

• Studies have shown that PAH clearance measured using microplate-based assay and HPLC method are in excellent agreement 2
• MRI-ASL kidney perfusion measurements have been shown to be related to measurements of renal plasma flow by PAH plasma clearance 6
• Iothalamate clearance has been shown to be a reliable method for estimating GFR and ERPF 4