Lecture 3

Question 1

What are the two renal functions that are tested?

Answer 1

GFR

Tubular Reabsorption

Question 2

What is GFR? What does it measure?

Answer 2

Glomerular Filtration Rate

Normally 125 ml/min (180 ml/day)

GFR measures the functioning of the nephron itself

Question 3

What occurs if GFR is low?

Answer 3

UREMIA

Uremia is a raised level in the blood of urea and other nitrogenous waste compounds that are normally eliminated by the kidneys

Uremia occurs if the GFR <10 ml/min

Question 4

How is Urea formed?

Answer 4

Urea is formed from the BREAKDOWN of amino acids

1. Amonia is produced from the DEAMINATION of amino acids performed by the liver. Amonia is very NEUROTOXIC and is usually high in those with Liver disease
2. The liver then converts amonia to urea

Question 5

What common laboratory tests of GFR?

Answer 5

BUN

Serum Creatine

Ratio of BUN/Creatine

Creatine Clearance

Question 6

Define BUN?

Answer 6

Blood Urea Nitrogen (BUN) test measures the amount of nitrogen in your blood that comes from the waste product urea.

Urea is made when protein is broken down in your body.

Urea is made in the liver and passed out of your body in the urine.

A BUN test is done to see how well your kidneys eliminating Urea

Question 7

When is a BUN test reliable?

Answer 7

BUN is only useful indicator of GFR if

1. If PROTEIN CATABOLISM is constant and normal
2. If VOLUME STATUS is also normal

Question 8

What is normal BUN?

Answer 8

10 - 20 mg/dl

Question 9

What are some reasons for a HIGH BUN?

Answer 9

HIGH BUN > 20 mg/dl

1. Hypovolemia (Dehydration)
2. High Catabolic State— (Trauma or Sepsis)
3. GI Bleeds (significant degradation in blood)
4. Hematoma (breakdown of blood)
5. High Protein Diet

BUN >50, usually d/t renal disease

Question 10

What are some reasons for a LOW BUN?

Answer 10

LOW BUN < 10 mg/dl

Starvation or potentially liver disease

BUN >50, usually d/t renal disease

Question 11

What is normal Serum Creatinine?

Answer 11

0.7 - 1.5 mg/dl

0. 6 - 1.0 Females
1. 8 - 1.3 Men

Slightly different due to difference in muscle mass

Question 12

If a lab test states that the Serum Creatine has DOUBLED, what would you expect to happen to GFR?

Answer 12

Doubling the serum creatinine usually means the GFR is DECREASED BY HALF

Question 13

What is the relationship between Creatinine and muscle mass?

Answer 13

Creatinine is DIRECTLY related to muscle mass

Question 14

What are some reasons for FALSE HIGH Creatinine levels?

Answer 14

1. Large Meat Meal
2. Cimetidine Therapy (like ranitidine H2 blocker - inhibits
   Creatinine secretion by renal tubules)
3. Ketoacidosis from elevated levels of acetoacetate (interferes with lab tests)

Question 15

What is the relationship between Creatinine and GFR?

Answer 15

Creatinine is INVERSELY related to GFR

Question 16

What happens to GFR and Creatinine levels with increasing age?

Answer 16

With age, muscle mass DECREASES

* GFR DECREASES 5% per decade

• However, this NOT reflected in Creatinine
  levels.

* THUS, a SMALL increase in Creatinine levels may mean a LARGER DECREASE in GFR

GFR will DECREASE with age, but creatinine level may stay the same

Decrease in number of functioning nephrons with age as well

Question 17

What is normal Ratio of BUN/Creatinine?

Answer 17

10:1

Question 18

What are some causes of LOW renal tubular flow?

Answer 18

Causes of LOW renal tubular flow:

DECREASED renal perfusion

Renal Obstruction of urinary tract

Question 19

What is the effect of LOW renal tubular flow on Urea? Creatinine?

Answer 19

LOW renal tubular flow:

Reabsorption of UREA

NO EFFECT on creatinine

Question 20

What is normal Creatinine Clearance?

Answer 20

110 - 150 ml/min