Lecture 5: Glomerular Filtration Surrogates: BUN, Creatinine, SDMA

Question 1

Endogenous

Answer 1

Produced by body, help to measure body function

Question 2

GFR

Answer 2

Measure of renal function, particularly functional renal mass

Question 3

GFR will change

Answer 3

Before routine blood chemistry changes

Question 4

GFR reference range

Answer 4

2.5 - 5 mL/min/kg BW

Question 5

Markers used for measuring GFR requirements

Answer 5

• Must be freely filtered
• Cannot be reabsorbed or secreted by renal tubule
• Can’t alter GFR
• Must be excreted only by kidneys, not metabolized

Question 6

What is the ideal GFR marker

Answer 6

Inulin

Question 7

Inulin type of marker

Answer 7

Fructose polymer

Question 8

Inulin is ________ and does not bind to _________

Answer 8

Freely filtered; plasma proteins

Question 9

Amount of inulin _____ is equal to the amount of inulin _____

Answer 9

Filtered; excreted

Question 10

Clearance of inulin =

Answer 10

GFR

Question 11

Filtration fraction

Answer 11

Expresses relationship between GFR and RPF, fraction of RPF filtered across glomerular capillaries in one pass

Question 12

Filtration fraction units

Answer 12

No units, can be % or decimal

Question 13

What is the typical filtration fraction of domestic animals?

Answer 13

10-40%

Question 14

What happens to the RPF that is not filtered?

Answer 14

Goes to peritubular capillaries

Question 15

Creatinine

Answer 15

Product of spontaneous, non-enzymatic breakdown of phosphocreatinine in muscle

Question 16

What action(s) do the kidneys take on creatinine?

Answer 16

Filtered and secreted only

Question 17

What rate is creatinine released into blood?

Answer 17

Relatively constant rate

Question 18

What causes the release of creatinine into the blood?

Answer 18

Muscle

Question 19

What % of functional nephrons are lost by the time creatinine increases above reference range?

Answer 19

75%

Question 20

What hides loss of GFR with creatinine

Answer 20

Loss of muscle mass

Question 21

In what patients will creatinine not leave reference range even when GFR severely impaired?

Answer 21

Patients with low muscle mass

Question 22

Loss of muscle mass =

Answer 22

Hiding loss of kidney function

Question 23

What is normal serum creatinine in dogs?

Answer 23

0.3 - 1.2 mg/dl

Question 24

Blood serum/urea nitrogen (BUN)

Answer 24

Synthesized in liver using ammonia (urea is nontoxic)

Question 25

Ammonia

Answer 25

By-product of amino acid metabolism and is toxic

Question 26

Rate at which BUN is produced

Answer 26

Not produced at constant rate

Question 27

Production of BUN can vary according

Answer 27

- Dietary protein uptake - Measuring during fasting or just after eating

Question 28

Normal BUN value in dog

Answer 28

8-25 mg/dl

Question 29

BUN:creatinine ratio, what does it mean when it increases?

Answer 29

BUN has increased (since in numerator)

Question 30

What happens to BUN:creatinine ratio in renal failure?

Answer 30

No change in ratio, both BUN and creatinine increase because GFR decreases so BUN + creatinine not removed from blood

Question 31

What happens to BUN:creatinine ratio in dehydration?

Answer 31

Increased BUN:creatinine ratio (increased BUN), since urea reabsorption increases to help with water reabsorption

Question 32

Urea reabsorption increases to help with

Answer 32

Water absorption

Question 33

Hypovolemia occurs due to

Answer 33

Shock or hemorrhage and reduced renal perfusions

Question 34

What is the kidney's response/action to hypovolemia?

Answer 34

Increase renal absorption of urea and decreases urea excretion, which increases plasma urea, which leads to pre-renal azotemia

Question 35

Increase in plasma urea leads to

Answer 35

Pre-renal azotemia

Question 36

Pre-renal azotemia

Answer 36

Abnormally high nitrogen compounds

Question 37

BUN:creatinine response to hypovolemia and pre-renal azotemia

Answer 37

Increased, because urea reabsorption to help with water reabsorption

Question 38

SDMA can be indicative of

Answer 38

Renal disease

Question 39

If SDMA increased and nothing else..

Answer 39

Have owner come back in 6 months, need more thsn one data point

Question 40

SDMA shows promise as a ______ for kidney function and is specific for _________

Answer 40

Biomarker; kidney function

Question 41

SDMA increases earlier than what as kidney function decreases

Answer 41

Creatinine

Question 42

SDMA diagnoses occur at what % loss of kidney function

Answer 42

40%

Question 43

How is SDMA effected by muscle mass?

Answer 43

Not

Question 44

When diagnosing kidney disease do not

Answer 44

Use a single marker in isolation

Question 45

Best practices for assessing kidney function in patients:

Answer 45

Consider history Do thorough physical examination Use urinary tract imaging Do a urinalysis, especially urine specific gravity Assess BUN, creatinine, and SDMA together