Nephrology - Equations

Question 1

Clearance

Answer 1

C = UV/P

Where:

C = Clearance (mL/min)

U = Urine concentration (mg/mL)

V = Urine volume/time (mL/min)

P = Plasma concentration (mg/mL)

Question 2

Renal Plasma Flow (RPF)

Answer 2

RPF = MAP/RVR

Where:

RPF = renal plasma flow (mL/min)

MAP = mean arterial pressure (mmHg)

RVR = renal vascualr resistance (mmHg/mL/min)

Question 3

Renal Plasma Flow (with PAH)

Answer 3

RPF = C_PAH = [U]_PAHV/[P]_PAH

Where:

RPF = renal plasma flow (mL/min)

C_PAH = clearance of PAH (mL/min)

[U]_PAH = urine concentration of PAH (mg/mL)

V = urine flow rate (mL/min)

[P]_PAH = plasma cncentration of PAH (mg/mL)

Question 4

Renal Blood Flow (RBF)

Answer 4

RBF = RPF / (1 - hematocrit)

Where:

RBF = renal blood flow (mL/min)

RPF = renal plasma flow (mL/min)

Question 5

Glomerular Filtration Rate (GFR)

Answer 5

GFR = [U]_inulinV/[P]_inulin

Where:

GFR = glomerular filtration rate (mL/min)

[U]_inulin = concentration of inulin in the urine (mg/mL)

V = urine flow rate (mL/min)

[P]_inulin = concentration of inulin the plasma (mg/mL)

Question 6

Glomerular Filtration Rate (GFR) using capillary and Bowman’s space pressures

Answer 6

GFR = K_f [(P_GC - P_BS) - (π_GC - π_BS)]

Where:

GFR = glomerular filtration rate

K_f = filtration coefficient

P_GC = hydrostatic pressure in the glomerual capillaries

P_BS = hydrostatic pressure in Bowman’s Space

π_GC = oncotic pressure in the glomerual capillaries

π_BS = oncotic pressure in Bowman’s Space

Question 7

Filtration Fraction

Answer 7

FF = GFR / RPF

Where:

FF = filtration fraction

GFR = glomerular filtration rate (mL/min)

RPF = renal plasma flow (mL/min)

Question 8

Filtered Load (FL)

Answer 8

FL = GFR · PC

Where:

FL = filtered load (mg/min)

GFR = glomerular filtration rate (mL/min)

PC = plasma concentraiton (mg/mL)

Question 9

Excretion Rate (ER)

Answer 9

ER = FL - RR

Where:

ER = excretion rate (mg/min)

FL = filtered load (mg/min)

RR = net reabsorption rate (mg/min)

Question 10

Reabsorption Rate (RR)

Answer 10

RR = FL - ER

Where:

RR = net reabsorption rate (mg/min)

FL = filtered load (mg/min)

ER = excretion rate (mg/min)

Question 11

Fractional Excretion (FE)

Answer 11

FE = amount excreted (mg) / amount filtered (mg)

Where:

FE = fractional excretion

Question 12

Henderson-Hasselbach Equation

Answer 12

pH = 6.1 + log [HCO₃^-] / (0.03 · PCO₂)

Where:

pH = the acidity of the blood

[HCO₃^-] = the concentration of HCO₃^- in the blood

PCO₂ = the partial pressure of CO₂ in the arterial blood

Question 13

Anion Gap

Answer 13

AG = Na⁺ - (Cl^- + HCO₃^-)

Where:

AG = anion gap

Question 14

Winter’s Formula

Answer 14

PCO₂ = 1.5[HCO₃^-] + 8 +/- 2

Where:

PCO₂ = the partial pressure of CO₂ in the arterial blood

[HCO₃^-] = the concentratsion of HCO₃^- in the blood