Renal Plasma Flow (RPF) Calculator

Determines RPF by the clearance of para-aminohippuric acid (PAH) which is a measure of renal function.

Refer to the text below the calculator for more information about this renal function measure and its formula.


Renal Plasma Flow (RPF) is a relevant measure of renal function but doesn’t belong to the category of routine nephrological investigatory methods because of the complexity of the determination with the involvement of renal clearance of para-aminohippuric acid (PAH) or radionuclide methods.

PAH clearance is essential for research studies in which the hemodynamic effects of various drugs are measured. For example, cardiac medication such as angiotensin-converting enzyme (ACE) inhibitors are associated with an increase in RPF.


Renal Plasma Flow (RPF) = [PAH] in urine x Urine flow rate (V) / [PAH] in plasma

Reference Ranges

Parameter Range Average
Renal Plasma Flow (RPF) 309 – 1,424 cc/min or ml/min 650 cc/min or ml/min
Urine flow rate (women) 600 – 1,260 cc/min or ml/min -
Urine flow rate (men) 900 – 1,080 cc/min or ml/min -

Urine flow rate (V)
Para-aminohippurate (PAH) in urine
Para-aminohippurate (PAH) in plasma
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Renal Plasma Flow Explained

Renal Plasma Flow (RPF) is a relevant measure of renal function but doesn’t belong to the category of routine nephrological investigatory methods because of the complexity of the determination with the involvement of renal clearance of para-aminohippuric acid (PAH) or radionuclide methods.

RPF determinations are based on the PAH clearance as at low concentrations, PAH is completely cleared from the plasma by renal glomerular filtration and tubular secretion in a single pass.

The concentration of PAH is measured in one arterial blood sample (PPAH) and one urine sample (UPAH). The urine flow (V) is also measured.

RPF x [PAH] in plasma = [PAH] in urine x Urine flow rate

Which in turn leads to:

Renal Plasma Flow (RPF) = [PAH] in urine x Urine flow rate / [PAH] in plasma

With:

  • Renal Plasma Flow - ml/min or cc/min;
  • [PAH] in urine or in plasma – in mg/ml;
  • Urine flow rate V – ml/min or cc/min.

Reference Ranges

Parameter Range Average
Renal Plasma Flow (RPF) 309 – 1,424 cc/min or ml/min 650 cc/min or ml/min
Urine flow rate (women) 600 – 1,260 cc/min or ml/min -
Urine flow rate (men) 900 – 1,080 cc/min or ml/min -

The clearance method calculates the effective renal plasma flow (eRPF) but some consider that since the renal extraction ratio of PAH almost equals 1, then eRPF almost equals RPF.

The renal extraction of PAH in healthy average individuals is approximately 0.92, which would in turn mean that the PAH clearance method underestimates RPF by 10% but this is considered an acceptable margin of error given the complexity of other measurement methods.

Renal plasma flow (RPF) decreases from a mean of 650 ml/min in the fourth decade to 290 ml/min by the ninth decade, with increasing renal vascular resistance. The decrease is more obvious in men than in women and in hypertensive patients.

The decrease in RPF does not simply reflect a decrease in renal mass but also one in renal blood flow with age.

PAH clearance is essential for research studies in which the hemodynamic effects of various drugs are measured. For example, cardiac medication such as angiotensin-converting enzyme (ACE) inhibitors are associated with an increase in RPF.

 

References

Reubi FC. Glomerular filtration rate, renal blood flow and blood viscosity during and after diabetic coma. Circulation Research. 1953; 1 (5): 410–3.

Blaufox MD, Merrill JP. Simplified hippuran clearance. Measurement of renal function in man with simplified hippuran clearance. Nephron. 1966; 3: 274.

Bradley SE, Curry JJ, Bradley GP. Renal extraction of p-aminohippurate in normal subjects and in essential hypertension and chronic diffuse glomerulonephritis. Fed. Proc. 1947; 6: 79.


Specialty: Nephrology

System: Urinary

Abbreviation: RPF

Article By: Denise Nedea

Published On: June 13, 2020 · 12:00 AM

Last Checked: June 13, 2020

Next Review: June 13, 2025