Water and Renal

Question 1

What are the major extracellular solutes?

Answer 1

Na, Cl and HCO3

Question 2

Calculate for the Intracellular and Extracellular volume in liters of a 73kg man with 40 liters total body water.

Answer 2

Intracellular 24 liters and Extracellular is 16 liters.
Remarks: total body water 60% of weight in kg.
Intracellular is 60% of tbw, extracellular is 40% of tbw. Plasma is 8%, Intercellular is 28%, Transcellular is 4%. PIT is under extracellular fluid.

Question 3

Gold standard for measurement of total body water?

Answer 3

Tritiated water or deuterium oxide (radioactive isotope)

Remarks: Both are very expensive.

Question 4

What is the definition of Osmolality and how is this measured?

Answer 4

OsmolaLity- number of moles of solute in kiLogram of solvent (water)
OsmolaRity- number of moles of solute in a liteR of solution
They are both measured based on colligative property.
Remarks: OsmolaLity is the preferred term.

Question 5

What is the formula of serum osmolality?

Answer 5

(2xNa)+(gluc/18)+(bun/2.8)
Na- mmol/L
Gluc and urea nitrogen- mg/dl

Question 6

What is the most important natriuretic peptide for renal exretion of sodium?

Answer 6

Urodilatin

Question 7

How many ml is the water loss from skin and the respiratory water loss per 100 calories?

Answer 7

30 ml from skin and 13 ml respiratory water loss per 100 calories.

Question 8

What is the formula of clearance?

Answer 8

C=UV/P unit is ml/min
U and P= concentration of substance in urine and plasma
V= volume of urine per unit time

Question 9

What is the best overall indicator of the level of kidney function?

Answer 9

Glomerular Filtration Rate (GFR)

Question 10

What is the gold standard for measuring glomerular filtration rate?

Answer 10

Inulin clearance

Question 11

Because inulin clearance is an expensive and time-consuming test, give an alternative in testing gfr?

Answer 11

Exogenous radioactive markers - 125 I-iothalamate and 99m Tc-DTPA (metastable technetium 99…)
Others: urea, creatinine (most widely used), cystatin C, beta trace protein, beta-2 microglobulin and tryptophan glycoconjugate. The first two are widely used.

Question 12

Why is Creatinine a good measure and most widely used for GFR?

Answer 12

1. Fairly constant rate of production
2. Not bound to plasma proteins therefore freely filtered by glomerulus
3. Not reabsorbed by the tubules
4. Only a small amount is secreted by the tubules

Question 13

What is the most widely used method in creatinine measurement and what is its principle/s?

Answer 13

Jaffe reaction or known as Alkaline picrate method
Creatinine reaction with trinitrophenol (picric acid or picrate)
Principle: Colorimetry + Spectrophotometry (NADH decrease absorbance at 340nm)

Question 14

What is the most definitive method for creatinine clearance?

Answer 14

IDMS (Isotope Dilution Mass Spectrometry)

Remarks: this is also the gold standard for urea measurement.

Question 15

What does presence of Cystatin C in urine indicate?

Answer 15

Proximal Tubular Damage

Note: There should be no Cystatin C in urine in the absence of proximal tubular damage.

Question 16

A measure of renal function that is associated with dialysis-associated amyloidosis?

Answer 16

Beta-2-Microglobulin

Question 17

In the presence of advance renal dysfunction, what is a better predictor of GFR?

Answer 17

Urea Clearance

Question 18

Inulin is to GFR and PAH (para-aminohippurate) is to ___?

Answer 18

Renal plasma flow

Question 19

What is the normal filtration fraction?

Answer 19

0.2

Note: Inulin clearance/ PAH clearance = filtration fraction

Question 20

A fractional excretion of less than 1% indicates ___?

Answer 20

Less than 1% FE means Prerenal azotemia.

More than 1% means Acute Tubular necrosis.

Question 21

What is the most specific and most sensitive acute kidney injury marker?

Answer 21

Kidney injury molecule-1 (KIM-1) - most specific

Neutrophil gelatinase-associated lipocalin (NGAL) - most sensitive

Question 22

What are the other acute kidney injury markers?

Answer 22

IL-18- proximal tubule injury, independent predictor of death.
Fatty acid-binding protein (Fabp)- proximal convoluted and straight tubule

Question 23

What is the Cockroft-Gault formula?

Answer 23

(140-age)xbody weight in kg/ 72 x serum creatinine concentration
x 0.85 for females
Note: This is used to estimate creatinine clearance.