# Effective Renal Plasma Flow Calculator (PAH Clearance)

Estimate ERPF from PAH clearance (C = U·V/P, normal ~500–700 mL/min), plus true RPF, renal blood flow from Hct, and filtration fraction from GFR. Not medical advice.

> Canonical page: https://elysiatools.com/en/tools/renal-plasma-flow

- **Category:** Health

- **Keywords:** renal plasma flow, erpf, pah clearance, para-aminohippuric acid, renal blood flow, filtration fraction, extraction ratio, kidney physiology, nephrology, rpf

## Overview

The Effective Renal Plasma Flow Calculator estimates ERPF using para-aminohippuric acid (PAH) clearance calculated from urine PAH, plasma PAH, and urine flow rate. It also computes true renal plasma flow (RPF) via the extraction ratio, total renal blood flow (RBF) using hematocrit, and the filtration fraction (FF) alongside glomerular filtration rate.

## Inputs

- **U — Urine PAH (mg/mL)** (number): Urine PAH concentration. Must use the same units as plasma PAH.
- **P — Plasma PAH (mg/mL)** (number): Plasma PAH concentration in the linear (non-saturating) range.
- **V — Urine Flow Rate (mL/min)** (number): Urine flow rate in mL/min.
- **PAH Extraction Ratio (optional)** (number): PAH extraction ratio E (fraction removed in one renal pass). Default 0.90.
- **Hematocrit (fraction, optional)** (number): Hematocrit as a fraction (0.45 = 45%). If provided, renal blood flow is computed.
- **GFR (mL/min, optional)** (number): Glomerular filtration rate in mL/min. Default 125; used for the filtration fraction.
- **Decimal Places** (number)

## When to use

- Calculating effective renal plasma flow (ERPF) and clearance from urine and plasma PAH concentrations.
- Deriving true renal plasma flow (RPF) and renal blood flow (RBF) with extraction ratio and hematocrit adjustments.
- Evaluating the renal filtration fraction (FF) by comparing glomerular filtration rate against calculated plasma flow.

## How it works

- Enter urine PAH concentration, plasma PAH concentration, and urine flow rate to calculate PAH clearance as C_PAH = (U · V) / P.
- Provide the PAH extraction ratio (default 0.90) to compute true renal plasma flow as RPF = ERPF / Extraction Ratio.
- Input hematocrit (fraction) to determine total renal blood flow as RBF = RPF / (1 - Hct) and enter GFR to compute filtration fraction as FF = GFR / RPF.

## Use cases

- Renal physiology education: Demonstrating clearance formulas, tubular secretion, and hemodynamic relationships.
- Experimental laboratory analysis: Quantifying kidney perfusion parameters from measured animal or human clearance data.
- Physiological research: Assessing alterations in renal blood flow and filtration fraction under various hemodynamic states.

## Frequently asked questions

### Why is PAH clearance used to estimate effective renal plasma flow?

PAH is freely filtered at the glomerulus and actively secreted by the proximal tubule, clearing almost all PAH from renal arterial plasma in a single pass.

### What is the normal ERPF range in healthy adults?

Normal effective renal plasma flow typically ranges between 500 and 700 mL/min for a standard adult body surface area.

### How does true RPF differ from ERPF?

ERPF assumes 100% extraction, whereas true RPF accounts for the actual PAH extraction ratio (typically around 0.90) using RPF = ERPF / E.

### How is renal blood flow calculated from plasma flow?

Renal blood flow (RBF) accounts for cellular blood volume by dividing true RPF by the plasma fraction: RBF = RPF / (1 - Hematocrit).

### What does the filtration fraction represent?

The filtration fraction (FF = GFR / RPF) represents the proportion of plasma entering the kidney that is filtered across the glomerulus, normally around 0.20.

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