Measurement of Kidney Function

Question 1

Basic Nephron Processes:

Answer 1

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Question 2

Clearance definition

Answer 2

the VOLUME of plasma completely cleared of a given substance in units/time (mL/min)

Question 3

Clearance equation

Answer 3

(glomerular filtration + tubular secretion) - Tubular rebasorption

Question 4

Renal clearance is a measurement of

Answer 4

excretion

Provides a summary of 3 basic renal functions:
- glomerular filtration (F)
- tubular re-absorption (R)
- tubular secretion (S)

Question 5

Glomerular Filtration Rate

Answer 5

the rate at which fluid is filtered at the glomerulus (ml/min)

Question 6

GFR is a measurement of renal function:

Answer 6

NO
Glomerular function only

Question 7

GFR vs Clearance:

Answer 7

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Question 8

Three Factors Determining Glomerular Filtration Rate:

Answer 8

• filtration pressures
• charge: -ve molecules filtered less
• size: proteins and blood cells too
  large less than 7KDa

Question 9

Effect of Renal Blood Flow: Afferent Arteriolar Constriction:

Answer 9

• fall in glomerular filtration pressure
• GFR falls

Question 10

Effect of Renal Blood Flow: Efferent Arteriolar Constriction:

Answer 10

• reduces blood flow
• but increases GFR due to increased
  filtration pressure
• however as renal blood flow further
  decreases
• GFR falls because filtration pressure
  can not be maintained at low levels
  of flow

Question 11

Control of GFR by Macula Densa:

Answer 11

• macula densa sense changes in
  sodium chloride delivery to DCT
• decreased GFR slows flow rat in
  Loop of Henle, causing increased
  reabsorption of the % Na+,Cl-
  delivered to ascending limb
• this:
  
  • decreases resistance to blood
    flow in afferent arteriole, which
    raises glomerular hydrostatic
    pressure, returning GFR to
    normal
  • increases renin release from JGA
    of afferent and efferent. Renin
    releases results in more
    Angiotensin II, increasing
    glomerular hydrostatic pressure,
    returning GFR toward normal

Question 12

Control of GFR by Macula Densa

Answer 12

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Question 13

Assessment of GFR (4):

Answer 13

• serum biochem
• measurement of clearance
• calaculated clearance
• renography

Question 14

Principles of Clearance:

Answer 14

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Question 15

Inulin Clearance:

Answer 15

the clearance of inulin is the virtual volume of blood that would be totally cleared of inulin in a given time (ml/min)

Question 16

Inulin Clearance equation

Answer 16

Urine(inulin)xVol(urine)/Plasma (inulin)

Question 17

Drawbacks of inulin clearance:

Answer 17

• needs infusion of inulin to achieve
  constant plasma conc
• blood sample to measure inulin
  conc
• timed urine collection and
  measurement of inulin in urine
• inaccurate urine volumes source of
  large error
• cumbersome for routine clinical use

Question 18

Creatinine:

Answer 18

• breakdown product of creatine
  phosphate in muscle
• generally produced at a constant
  rate
• can be altered with large muscle
  mass, cachexia, pregnancy, liver
  disease and durgs like trimethoprim
• normal range 40-120 micromol/L in
  plasma

Question 19

Creatinine Clearance: Definition:

Answer 19

the virtual volume of blood that would be totally cleared of creatinine in a given time (ml/in)

Question 20

Creatinine Clearance Equation

Answer 20

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Question 21

Drawbacks of Creatinine Clearance:

Answer 21

• inaccurate urine volumes are a
  source of large error
• does not tell you about the
  proportion of the creatinine filtered
  vs secreted
• overestimates GFR at low levels of
  GFR

Question 22

What is inulin?

Answer 22

sugar
not produced in the body
experiments: no reabsorption/secretion so useful

Question 23

Advantage of using creatinine clearance vs inulin clearance:

Answer 23

• does not require constant infusion
• both have urine volume inaccuracies
• due to secretions OVERESTIMATE
  GFR because of creatinine secretions

Question 24

estimation of clearance using plasma creatinine and what does this formula take into account?

Answer 24

CKD-EPI (chronic kidney disease epidemiology) (more accurate because actually used normal pts) (no mass so wastin away/obese not accurate)

Question 25

What does the cockcroft gaut formula take into account?

Answer 25

mass and age

Question 26

estimation of clearance using renography

Answer 26

• chromium 51 EDTA
• radioactive tag
• allows estimation of GFR without
  having to collect urine samples

Question 27

What is the group of blood tests that measure renal function?

Answer 27

Urea & Electrolytes

Question 28

Urea & Electrolytes involve (5):

Answer 28

• sodium
• potassium
• creatinine
• AKI stage (acute kidney injury)
• estimated GFR

Question 29

Renal Function Measurements: Arterial Blood Gases:

Answer 29

• pH
• HCO3-
• Lactate

Question 30

Urinanalysis:

Answer 30

• what components in urine:
  - protein
  - leukocytes
  - blood
  - ketones
  - glucose
  - billirubin

Question 31

List the different tests for renal function:

Answer 31

• blood tests: U&E, ABGs
• Urinanalysis
• estimated GFR (creatinine/inulin)
• Renography

Question 32

Serum Creatinine as a Measure of Kidney Function:

Answer 32

• normal GFR can drop to 50% before
  creatinine goes above upper limit of
  normal
• not good at detecting early renal
  disease
• in later stages of renal disease there
  are large changes in creatinine but
  very little changes in GFR/ renal
  function
  INSERT

Question 33

Diagnosis of Kidney Dysfunction:

Answer 33

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Question 34

Monitoring of Kidney Function:

Answer 34

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Question 35

Functions of the Kidney:

Answer 35

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Question 36

Serum Creatinine as a Measure of Kidney Function:

Answer 36

• normal GFR can drop to 50% before
  creatinine goes above upper limit of
  normal
• not good at detecting early renal
  disease
• in later stages of renal disease there
  are large changes in creatinine but
  very little changes in GFR/ renal
  function
  INSERT