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Year 2 Urinary > Kidney Clearance > Flashcards

Kidney Clearance Flashcards

1
Q

What does the kidney regulate?

A 
BP
Blood volume 
pH
Electrolytes 
Osmolality
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2
Q

What does the kidney excrete?

A

Waste products and drugs

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3
Q

Drugs, hormones and proteins are …. by the kidney

A

Metabolised

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4
Q

What is the endocrine function of the kidney?

A

1-alpha calcidol
renin
erythropoetin

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5
Q

Which area of the nephron is primarily assessed clinically?

A

Glomerulus

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6
Q

What is GFR?

A

Glomerular filtration rate

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7
Q

Why does the GFR drop after age of 30?

A

GFR deteriorates by 6-7ml/min per decade because there is a drop in nephron number

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8
Q

With age what happens to the size of the kidney?

A

Gets smaller - the cortex thins (smaller glomerulus so reduced GFR)

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9
Q

In what type of person is a smaller kidney more problematic?

A

Big people

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10
Q

What happens in compensatory hypertrophy?

A

If one kidney functions poorly the other kidneys nephrons will hypertrophy to compensate- get bigger and work harder

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11
Q

What is the side effect of a compensatory hypertrophy?

A

Nephron has to work harder and gets worn out

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12
Q

Before 36 weeks gestation if there is a problem with one kidney what happens to the other?

A

The nephrons will hypertrophy and undergo hyperplasia - tends to function normally and not be predisposed to wearing out

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13
Q

In what physiological state does GFR increase and renal glucose threshold decrease?

A

Pregnancy

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14
Q

What does GFR increase to in pregnancy?

A

130-180ml/minute- up to 50% increase

90-110ml/min is normal in a non-pregnant woman

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15
Q

Does the nephron number change in pregnancy?

A

No but the kidney will increase in size by about 1cm to deal with the increased fluid in the woman.

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16
Q

How long after delivery will a woman kidneys take to return to normal size and function?

A

6 months

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17
Q

Why might a persons GFR decrease?

A

Reduced nephron number

GFR in each nephron is reducing.

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18
Q

Why in a slowly deteriorating kidney is GFR change not detectable till late stages of disease?

A

Compensatory hypertrophy

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19
Q

What is the formula for clearance?

A

C=A/P (conc of sunstance eleiminated / conc of substance in plasma)
Clearance is the amount of a substance cleared in a given unit of time

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20
Q

What is renal clearance?

A

excretion rate/ plasma conc

21
Q

How do you calculate excretion rate?

A

Amount in urine/ urine flow rate

22
Q

We can use substances to measure GFR, what qualities should a substance we use to measure GFR have?

A
  • constant production
  • 100% filtration in glomerulus
  • no reabsoprtion in the distal tubule
  • not secreted
23
Q

What is inulin and how is it used?

A

Inulin is a drug given IV to assess GFR. It is good, but needs continuous IV delivery and urine needs to be collected via catheters.

24
Q

What radioactive labelled marker may be used to assess GFR?

A

51 Cr-EDTA

25
Q

List the advantages and disadvantages of 51 Cr-EDTA for GFR assessment

A

Advantages- cleared exclusively by renal filtration. No urine collection. Suitable for children pre kidney transplant.
Disadvantages- Radioactive labelled marker- not to be used in pregnancy. 10% lower than clearance (reabsorbed?). 2,3,4 hourly blood tests after injection/

26
Q

What endogenous marker is a good estimate of GFR?

A

Creatinine (it is produced at a rate proportional to muscle mass - unless other pathology, its freely filtered and not reabsorbed. There is some secretion however)

27
Q

What does secretion of creatinine mean interns of the eGFR it gives?

A

The secretion means the eGFR is overestimated when looking at creatinine (10-20%)

28
Q

How do we assess creatinine clearance?

A

Urine collection over 24 hours

29
Q

Who is creatinine useful for and why is it cumbersome?

A

Pregnant women - endogenous substance

Carrying urine bottles

30
Q

What is a normal serum creatinine measurement?

A

132micromol/L

31
Q

How do we get and get rid of creatinine?

A 
Intake (dietary)
Muscle mass/ Metabolism 
Renal secretion 
Renal excretion 
Extra renal secretion
32
Q

If renal excretion declines with a GFR decline what will take over creatinine removal?

A

Renal SECRETION will increase

Extra renal excretion

33
Q

What factors increase serum creatinine?

A 
Muscle break down 
Muscle Mass 
Male 
Black 
Supplementation 
Meat in diet 
Drugs like trimethoprim
34
Q

An elderly hispanic lady presents with reduced muscle mass and is vegetarian what could you predict about her serum creatinine?

A

Likely to be lower

35
Q

If we use serum creatinine to assess GFR what else must we consider?

A

The person (a big muscly black man will have higher creatinine irrespective of GFR than when compared to an elderly indoasian woman)

36
Q

At birth what is the creatinine of the neonate?

A

The same as the mother (this will rapidly drop and then gradually increase again)

37
Q

What is a maternal creatinine at birth?

A

Increased GFR means creatinine in pregnant woman is low (she’s filtering more out)

38
Q

Is serum creatinine a sensitive marker for GFR deterioration?

A

No, 50% loss of GFR before creatinine effected. Compensatory hypertrophy and increased secretion hides a subtle problem.

39
Q

If you look at inulin clearance (true GFR) and compare it with serum creatinine why is the GFR predicted by GFR lower?

A

Creatinine secretion

40
Q

Serum creatinine is used for what in terms of renal function

A

eGFR

not GFR, its just a best guess

41
Q

What does the MDRD eGFR used by UHL consider when calculating eGFR?

A

Serum Creatinine
Age
Sex
Caucasian or Black

42
Q

What body surface area do we standardise to and what does this mean?

A

1.73m2

we don’t need to consider height and weight —- really big or really small people get an inaccurate result

43
Q

Who is an MDRD eGFR less accurate in?

A 
People without kidney disease (transplant donors)
Children 
Pregnancy 
Old Age
Non Black or caucasians 
Reduced muscle mass/ amputees 
High renal function patients >60mls/min

Acute Kidney injury (needs a gradual change to detect )

44
Q

Why should you be careful not to label a patient with chronic kidney disease on the basis of eGFR alone?

A

It underestimates true GFR if its close to normal range

You need to look at if an individuals GFR changes and always consider what else could be effecting a serum creatinine

45
Q

What is CKD-EPI?

A

Like MDRD with a slightly different calculation used in other hospitals. Better when eGFR>60mls/min

46
Q

Serum creatinine will …. estimate GFR in normals.

A

UNDER >60mls/min

47
Q

Why does eGFR get OVER estimated in CKD patients?

A

Compensatory hypertrophy with increased renal secretion and a reduction in GFR will initially cause increase in renal blood flow to compensate

48
Q

Why do bigger people have higher GFRs?

A

Bigger kidneys in bigger people.

Remember that they are likely to have higher serum creatinine from larger muscle mass

Year 2 Urinary (9 decks)

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