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Physiology I Exam 2 > Lecture 5: Glomerular Filtration Surrogates: BUN, Creatinine, SDMA > Flashcards

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

1
Q

Endogenous

A

Produced by body, help to measure body function

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2
Q

GFR

A

Measure of renal function, particularly functional renal mass

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3
Q

GFR will change

A

Before routine blood chemistry changes

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4
Q

GFR reference range

A

2.5 - 5 mL/min/kg BW

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5
Q

Markers used for measuring GFR requirements

A
  • Must be freely filtered
  • Cannot be reabsorbed or secreted by renal tubule
  • Can’t alter GFR
  • Must be excreted only by kidneys, not metabolized
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6
Q

What is the ideal GFR marker

A

Inulin

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7
Q

Inulin type of marker

A

Fructose polymer

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8
Q

Inulin is ________ and does not bind to _________

A

Freely filtered; plasma proteins

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9
Q

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

A

Filtered; excreted

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10
Q

Clearance of inulin =

A

GFR

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11
Q

Filtration fraction

A

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

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12
Q

Filtration fraction units

A

No units, can be % or decimal

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13
Q

What is the typical filtration fraction of domestic animals?

A

10-40%

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14
Q

What happens to the RPF that is not filtered?

A

Goes to peritubular capillaries

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15
Q

Creatinine

A

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

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16
Q

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

A

Filtered and secreted only

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17
Q

What rate is creatinine released into blood?

A

Relatively constant rate

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18
Q

What causes the release of creatinine into the blood?

A

Muscle

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19
Q

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

A

75%

20
Q

What hides loss of GFR with creatinine

A

Loss of muscle mass

21
Q

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

A

Patients with low muscle mass

22
Q

Loss of muscle mass =

A

Hiding loss of kidney function

23
Q

What is normal serum creatinine in dogs?

A

0.3 - 1.2 mg/dl

24
Q

Blood serum/urea nitrogen (BUN)

A

Synthesized in liver using ammonia (urea is nontoxic)

25
Q

Ammonia

A

By-product of amino acid metabolism and is toxic

26
Q

Rate at which BUN is produced

A

Not produced at constant rate

27
Q

Production of BUN can vary according

A
  • Dietary protein uptake
  • Measuring during fasting or just after eating
28
Q

Normal BUN value in dog

A

8-25 mg/dl

29
Q

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

A

BUN has increased (since in numerator)

30
Q

What happens to BUN:creatinine ratio in renal failure?

A

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

31
Q

What happens to BUN:creatinine ratio in dehydration?

A

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

32
Q

Urea reabsorption increases to help with

A

Water absorption

33
Q

Hypovolemia occurs due to

A

Shock or hemorrhage and reduced renal perfusions

34
Q

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

A

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

35
Q

Increase in plasma urea leads to

A

Pre-renal azotemia

36
Q

Pre-renal azotemia

A

Abnormally high nitrogen compounds

37
Q

BUN:creatinine response to hypovolemia and pre-renal azotemia

A

Increased, because urea reabsorption to help with water reabsorption

38
Q

SDMA can be indicative of

A

Renal disease

39
Q

If SDMA increased and nothing else..

A

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

40
Q

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

A

Biomarker; kidney function

41
Q

SDMA increases earlier than what as kidney function decreases

A

Creatinine

42
Q

SDMA diagnoses occur at what % loss of kidney function

A

40%

43
Q

How is SDMA effected by muscle mass?

A

Not

44
Q

When diagnosing kidney disease do not

A

Use a single marker in isolation

45
Q

Best practices for assessing kidney function in patients:

A

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

Physiology I Exam 2 (12 decks)

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