CP4-3 renal function tests and hydration status

Question 1

What are the 5 main functions of the kidney?

Answer 1

Fluid balance
Removal of waste products from the blood
BP maintenance by balancing Na, K and water
Bone mineralisation (1,25 hydroxy vit D)
RBC production

Question 2

What is the functional unit of the kidney?

Answer 2

Nephron

Question 3

What is polyuria?

Answer 3

Urine output >3000ml/24 hours

Question 4

What volume of urine excretion is normal?

Answer 4

750-2000ml/24hrs

Question 5

What is oliguria?

Answer 5

Urine output <400ml/24hrs

Question 6

What is anuria?

Answer 6

Urine output if <100 ml/24hrs

Question 7

What is the reference range of blood sodium?

Answer 7

133-146 mmol/L

Question 8

What is the reference range for blood potassium?

Answer 8

3.5-5.3 mmol/L

Question 8

What is the reference range for blood urea?

Answer 8

2.5-7.8 mmol/L

Question 9

What is the reference range for blood creatinine?

Answer 9

49-90 umol/L

Question 10

What can affect how EGFR value is interpreted?

Answer 10

Muscle mass

Question 11

What tests of renal function should be done when kidney disease is suspected?

Answer 11

Glomerular filtration rate
Estimate EGFR
Creatinine clearance
Plasma creatinine levels
Plasma urea
Assess urine - volume, urea, sodium, protein, glucose, haematuria (can check with urinalysis dipstick test)

Question 12

What pre-renal factors affect renal function by impairing kidney perfusion?

Answer 12

Cardiac failure
Sepsis
Blood loss
Dehydration
Vascular occlusion

Question 13

What renal factors affect renal function?

Answer 13

Glumerulonephritis
Small vessel vasculitis
Acute tubular necrosis as a result of drugs, toxins or prolonged hypotension
Interstitial nephritis due to drugs, toxins, inflammatory disease or infection

Question 14

What post-renal factors affect renal function?

Answer 14

Urinary calculi
Retroperitoneal fibrosis
Benign prostatic enlargement
Prostate cancer
Cervical cancer
Urethral stricture/valves
Meatal stenosis/phimosis

Question 15

What is the reference range for plasma urea?

Answer 15

3-8 mmol/L

Question 16

What causes more urea to be reabsorbed into the blood at the glomerulus?

Answer 16

A slow rate of tubular flow

Question 17

What % of urea is reabsorbed by renal tubules in healthy kidneys?

Answer 17

40%

Question 18

What causes a slow tubular flow rate in the kidneys?

Answer 18

Renal hypotension

Question 19

What causes an increased production of urea?

Answer 19

GI bleed
Surgery, infection, trauma
Drugs e.g. steroids and tetracyclines
Cancer
High protein diets

Question 20

What causes a decreased excretion of urea?

Answer 20

Pre-renal, renal and post-renal factors

Question 21

What is the reference range for plasma creatinine?

Answer 21

50-140 umol/L (dependent on muscle mass)

Question 22

What is the relationship between plasma creatinine levels and glomerular flow rate (GFR)?

Answer 22

As concentration of plasma creatinine increase, GFR decreases

Question 23

Plasma creatinine is not proportional to renal damage. True or false?

Answer 23

True

Question 24

What is a by product of DKA?

Answer 24

Acetoacetate

Question 25

Why are plasma creatinine tests inaccurate in patients who have had a paracetamol overdose ?

Answer 25

The overdose is treated with N-acetyl cysteine which makes creatinine levels look like they’ve improved even if they haven’t.

Question 26

What level may plasma creatinine reach in patients with chronic renal disease?

Answer 26

1000 umol/L

Question 27

What is a plot of reciprocal plasma creatine concentration used to predict in patients with chronic renal disease?

Answer 27

When intervention for end stage renal failure is required

Question 28

How is creatinine clearance calculated?

Answer 28

Dividing the urine creatinine concentration (mmol/L) multiplied by the volume of urine (ml collected in 24 hours) by the plasma creatinine (umol/L)

Question 29

What is the reference range for creatinine clearance?

Answer 29

100-130 ml/min)

Question 30

What can cause an increased tubular secretion of creatinine?

Answer 30

Chronic renal disease

Question 31

What can cause tubular secretion of creatinine to be inhibited?

Answer 31

Drugs like salicylate and cimetidine

Question 32

What are disadvantages of working out creatine clearance?

Question 33

What does high creatine clearance mean for kidney function?

Answer 33

Good kidney function

Question 34

What does low creatinine clearance mean about kidney function?

Answer 34

Low kidney function

Question 35

How does plasma change when creatine clearance is between 30-60ml/min?

Answer 35

increased creatine and urea

Question 36

How does plasma change when creatinine clearance is between 20-30ml/min?

Answer 36

increased potassium and decreased bicarbonate

Question 37

How does plasma change when creatinine clearance is between 10-20ml/min?

Answer 37

Increased phosphate and increased uric acid

Question 38

What caused issues when EGFR was originally introduced?

Answer 38

Calculated using a different formula Creatine tests are different in different places

Question 39

How has EGFR been made more reliable?

Answer 39

Standardisation of formula for determining eGFR

Question 40

What is stage 1 renal function with GFR of 90+?

Answer 40

Normal kidney function

Question 41

What is stage 2 kidney function with GFR of 60-89?

Answer 41

Mildly reduced kidney function and associated findings of kidney disease

Question 42

What is stage 3A and 3B kidney function with GFR of 45-59 and 30-44 respectively?

Answer 42

Moderately reduced kidney function

Question 43

What is stage 4 kidney function with GFR of 15-29?

Answer 43

Severely reduced kidney function requiring planning for end stage renal failure

Question 44

What is stage 5 kidney function with GFR of <15 or on dialysis?

Answer 44

Very severe or endstage kidney failure aka established renal failure requiring dialysis and transplant

Question 45

What happens to potassium levels in acute kidney injury?

Answer 45

Potassium levels increase

Question 46

How can you tell from trends in creatinine levels whether a patient with chronic kidney disease is on dialysis?

Answer 46

The creatinine levels would go down after dialysis and then increase again. If not on dialysis, levels will be stable/won’t fluctuate.

Question 47

What happens to urea levels when there is an upper GI bleed?

Answer 47

It increases and reduces again when bleeding is stopped.

Question 48

How can you determine if increased urea on a kidney function test is due to a bleed elsewhere or due to damage to the kidneys?

Answer 48

The increase in urea will be isolated. eGFR will drop due to drop in blood pressure and slight increase in creatinine.