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Test your knowledge of the criteria used to assess and classify acute kidney injury and chronic kidney disease.

Reviewed by Daniel Mercer on 3rd October 2019

AKI and CKD

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Question 1
Lupus is an autoimmune condition that can sometimes target the nephrons in the kidney leading to renal failure. What type of renal failure is this an example of?
A
Pre-renal failure
B
Intrinsic renal failure
C
Post-renal failure
Question 1 Explanation: 
Because the nephrons are being damaged and the nephrons are IN the kidney, this is an example of INtrinsic renal failure. Intrinsic renal failure relates to any part of the kidney.
Question 2
Which of the following conditions is most likely to be responsible for pre-renal failure?
A
Pyelonephritis
B
Struvite stones
C
Sepsis
D
Enlarged prostate
E
Spinal cord damage in the region of L5
Question 2 Explanation: 
Pre-renal failure is normally the result of hypo-perfusion of the kidneys therefore you are looking for something that could reduce blood supply to the kidneys. Sepsis causes is drop in blood pressure so the kidneys wouldn't receive enough blood, or enough blood at the right pressure, to adequately perfuse the kidneys.

The four other examples are arguably all examples of post-renal failure, that is characterised by blockage of renal drainage. Pyelonephritis causes inflammation and pus build up in the pelvis of the kidney preventing it from draining. Struvite stones also form in the renal pelvis. An enlarged prostate could stop bladder drainage causing urine to back up into the kidneys. Similarly, spinal cord damage at L5 could damage the parasympathetic nerves (aka pelvic splanchnic nerves) that exit the vertebral column S2-4. These nerves provide motor innervation to the bladder and their damage could cause urinary retention.

Question 3
Which substance is used to estimate GFR?
A
Creatine kinase
B
Albumin
C
Inulin
D
Creatinine
E
Glucose
Question 3 Explanation: 

eGFR (glomerular filtration rate) estimates how much creatinine is cleared by the kidneys by measuring the serum creatinine (i.e. creatinine in the blood) and adjusting this value based on age, sex, weight and sometimes ethnicity (see update below).

It might be easy to confuse this with creatine kinase, an enzyme released from damaged muscle, but they are separate substances.

Inulin can be used for calculating the true GFR as it is filtered by the glomeruli is not reabsorbed nor secreted elsewhere in the nephron.

UPDATE (May 2022): In November 2021, ethnicity was removed as a factor for calculating CKD-EPI (the preferred standard for estimating GFR) and an option to include cystatin C in the calculation was also added. For further information see: https://pubmed.ncbi.nlm.nih.gov/34554658/. The MDRD formula still includes ethnicity.

Question 4
For each of the following four questions, use the given information to give the patient's RIFLE classification. Can't remember the criteria? See here or here.
A male patient whose baseline creatinine was 102 uM and is now 227 uM. Their eGFR has reduced by 35 percent.
A
Risk
B
Injury
C
Failure
D
Loss
E
End-stage renal disease
Question 4 Explanation: 
Their creatinine levels have more than doubled from the baseline. Although eGFR hasn't decreased by more than 50 percent, the criteria use the worst-case to determine the classification.
Question 5
A patient on dialysis for the last two months.
A
Risk
B
Injury
C
Failure
D
Loss
E
End-stage renal disease
Question 5 Explanation: 
Dialysis is a type of renal replacement therapy (RRT) therefore the patient is either going to classified as loss or ESRD. However, as they have not been on dialysis for more than three months, they are classified as Loss.
Question 6
A patient with a baseline serum creatinine of 94 uM, now showing a level of 300 uM, and an eGFR reduced by 75 percent
A
Risk
B
Injury
C
Failure
D
Loss
E
End stage renal disease
Question 6 Explanation: 
These are both criteria for a classification of Failure.
Question 7
A 90 kg patient who hasn't produced more than 40 ml or urine per hour in the last 6 hours.
A
Risk
B
Injury
C
Failure
D
Loss
E
End-stage renal disease
Question 7 Explanation: 
The patient weights 90 kg. Dividing this by 2 gives us 45, which is the minimum volume of urine in ml we expect them to produce each hour. The patient has not produced this for eight hours, therefore they are at Risk.
Question 8
A RIFLE classification of failure is equivalent to which Acute Kidney Injury Network (AKIN) score? Forgotten what the AKIN scores are? See here and here.
A
1
B
2
C
3
D
4
E
5
Question 9
How many months of renal damage is required for a diagnosis of chronic kidney disease?
A
1
B
2
C
3
D
4
E
5
Question 10
What two tests are used to calculate the associated risk of complications from CKD?
A
eGFR
B
Serum creatinine
C
Serum albumin
D
ACR
E
Urea and electrolytes (U&Es)
Question 10 Explanation: 
ACR is the albumin:creatinine ratio and shows how much albumin is present in the urine. It is compared against creatinine to take account of urine concentration. Albumin shouldn't appear in the urine; it is the largest protein in the body so finding it in the urine indicates damage to the nephrons.
Question 11
Which of the following are considered normal eGFRs? (Tick all the apply)
A
68
B
94
C
89
D
104
E
61
Question 11 Explanation: 
A GFR of more than 90 is considered 'normal'.
Question 12
Which patient below has a 'severe reduction' in their GFR (classified as G4)? See here for a reminder.
A
Patient A - 41
B
Patient B - 69
C
Patient C - 21
D
Patient D - 37
E
Patient E - 30
Question 12 Explanation: 
A severe reduction in GFR is a GFR between 15 and 29. Look at the NICE guidelines (https://www.nice.org.uk/guidance/cg182/chapter/1-Recommendations#classification-of-chronic-kidney-disease-2) and you'll see that there is a rough pattern of increments of 15 and 30 which might help you remember.
Question 13
Which patients have a mild reduction in GFR? (Tick all that apply)
A
Patient A - 21
B
Patient B - 97
C
Patient C - 78
D
Patient D - 60
E
Patient E - 30
Question 13 Explanation: 
A moderate reduction in GFR is in the range 60-89
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