Renal 03: Gfr And Proteinuria

Front 1

What is the equation for Q_filt (filtration flow)?

Back 1

Q filt = GFR * [serum]

Front 2

What is the equation for Q_excr (excretion flow)?

Back 2

Q excr = UFR (urine flow rate) * [urine]

Front 3

What is the equation for GFR? What is it dependent on?

Back 3

GFR = (UFR * [urine]) / [serum]

If Q filt = Q excr

Front 4

Why is creatinine used to assess GFR?

Back 4

- Creatinine is produced on constant basis by metabolism of muscle creatine
- Freely filtered by glomeruli and minimally secreted by tubules
- Good marker for GFR

Front 5

What are the normal values for serum creatinine in men? Women? Children?

Back 5

Men: 0.9 - 1.3 mg/dl
Women: 0.8 - 1 mg/dl
Children: 0.5 - 1 mg/dl (starts low and gets greater with age, d/t increased muscle mass)

Front 6

How much can serum creatinine vary based purely on analytical technique?

Back 6

10%

Front 7

Why are serum creatinine levels lower in women and children?
Men: 0.9 - 1.3 mg/dl
Women: 0.8 - 1 mg/dl
Children: 0.5 - 1 mg/dl

Back 7

Women and children have less muscle mass on average than men

Front 8

How do you calculate Creatinine Clearance?

Back 8

Cr Cl = (UFR * [urine]) / [serum]

UFR needs to be in ml/min

Front 9

How does halving the glomeruli area affect GFR? Serum conc. of creatinine? Urine conc. of creatinine?

Back 9

- GFR will be halved
- Serum conc. will eventually double
- Urine conc. will initially halve, but eventually returns to normal value

Front 10

What is another way to estimate GFR? How does it compare to Creatinine?

Back 10

- Inject inulin because it is freely filtered and not secreted or reabsorbed
- More accurate than creatinine clearance (creatinine slightly overestimates d/t some secretion)
- Rarely done in real life, but often in research

Front 11

What GFR values correspond to stages of chronic kidney disease?

Back 11

- Normal: >100 ml/min
- Stage I: ≥90 ml/min
- Stage II: 60-89 ml/min
- Stage III: 30-59 ml/min
- Stage IV: 15-29 ml/min
- Stage V: <15 ml/min

Front 12

At what GFR do you need dialysis (or kidney transplant)?

Back 12

GFR < 10 ml/min

Front 13

How is GFR related to serum creatinine?

Back 13

Inverse relationship between serum creatinine and GFR (inulin clearance)

Front 14

How is GFR calculated in the medical setting?

Back 14

- MDRD Formula (don't need to know eqn)
- There are modifiers based on gender, race, and age to estimate GFR from serum creatinine
- Also related to body surface area (BSA)

- Also Cockcroft-Gault Formula (takes into account age, weight, gender, and serum creatinine)

Front 15

What is BUN? How does it relate to GFR?

Back 15

- Nitrogenous waste product
- Increased BUN as GFR declines

- Elevated BUN indicative of poor kidney function

Front 16

What do we need to understand as we are trying to calculate the GFR?

Back 16

Estimates of GFR with equations are IMPRECISE

Front 17

What can cause an acute (rapid) change in GFR?

Back 17

Drop in BP, sepsis, etc.

Front 18

What happens in response to an acute drop in GFR (eg, d/t suddenly low BP, sepsis)?

Back 18

- Serum conc. gradually increases
- Urine flow of creatinine slows down but gradually recovers as serum conc. increases

Front 19

How can you assess for protein in urine?

Back 19

- Urine dipstick
- Urinalysis

Front 20

What can you assess on urine dipstick?

Back 20

- Proteinuria
- Hematuria
- Urine pH

Front 21

How can you quantify urine protein?

Back 21

- 24 hour urine collection (this is annoying)
- Spot urine sample (should be relatively stable, so this should be good representative of 24 hour collection)

Front 22

What causes proteinuria?

Back 22

Glomerular disease → glomerular protein leak overwhelms tubular re-absorption

Front 23

What are the outcomes of protein in urine (d/t glomerular disease)?

Back 23

Glomerular protein leak overwhelms tubular reabsorption → loss of albumin → low plasma oncotic pressure → Edema

Front 24

What causes edema?

Back 24

- Glomerular Injury →
- Glomerular protein leak overwhelms tubular reabsorption →
- Loss of albumin →
- Low plasma oncotic pressure →
- Edema

Front 25

What is the maximum amount of urine protein in healthy patients?

Back 25

150 mg / day (not detected on urinalysis)

Front 26

How is proteinuria graded?

Back 26

Semi-quantitatively: 1, 2, 3, 4+

Front 27

**What can cause nephrotic syndrome w/ edema?

Back 27

**Urine protein more than 3g/day

Front 28

What do the images on L and R represent?

Back 28

L = normal
R = membranous GN (glomerulonephritis) - capillary loops are too thick, too much pink stuff

Front 29

What is the definition / diagnostic of micro-albuminuria?

Back 29

- 30 - 300 mg albumin / 24 hours OR
- 20 - 30 µg / minute OR
- 30 - 300 mg albumin / g of creatinine

Front 30

What does micro-albuminuria represent?

Back 30

This does not mean "small albumin", rather it means levels of albumin that are not usually detectable on urine dipstick (30 - 300 mg albumin / g of creatinine)

= Gray zone

(Precursor of kidney disease)

Front 31

What is the normal amount of albumin in urine?

Back 31

< 30 mg albumin / g of creatinine (below gray box)

Front 32

How does the width of the glomerular basement membrane change in diabetes, micro-albuminuria, proteinuria? Implications?

Back 32

- Normal: ~300 nm
- Diabetes: some in normal range but some already w/ wider GBM
- Micro-albuminuria: wider GBM
- Proteinuria: widest GBM

Protein leaks through GBM when thickened

Front 33

What is another possible explanation for proteinuria?

Back 33

Not d/t kidney disease, but rather d/t overflow or overproduction of proteins (increased in multiple myeloma)