Renal Function and Disease

Question 1

What is the best measure of renal function?

Answer 1

Glomerular filtration rate

Question 2

What is used to measure GFR?

Answer 2

In day to day practice, creatinine is used.

For more serious measurements, Cr-EDTA is used.

The gold standard (used in research) is to use Inulin.

Question 3

What can a simple sample be now used to investigate?

Answer 3

• Dipstick (blood, nitrites, glucose, leucocytes, ketones)
• Protein quantification
• Microscopy

Question 4

What is a 24 hour urine needed for?

Answer 4

• Creatinine clearance estimation

- Stone forming elements

Question 5

What can urine microscopy be used to investigate?

Answer 5

• Crystals
• Red blood cells
• White blood cells
• Casts
• Bacteria

Question 6

In urine microscopy, what does the presence of calcium oxalate crystals mean?

Answer 6

Anti-freeze (ethylene glycol) poisoning

Question 7

What types of renal imaging are there?

Answer 7

• USS
• CT
• Dynamic renal imaging (paediatrics)

Question 8

What renal imaging is best for renal stones?

Answer 8

CT KUB

Question 9

What is acute kidney injury?

Answer 9

AKI is a rapid decline in renal function, measured in stages.

Question 10

What are the stages of AKI?

Answer 10

Urine output of <0.5ml/kg/hour

Stage 1: 1.5-1.9x serum creatinine
Stage 2: 2-2.9x serum creatinine
Stage 3: >3x serum creatinine

Question 11

What are the causes of AKI?

Answer 11

These can be pre-renal, renal or post-renal

Pre-renal:
- Reduced perfusion

Renal:
- Vascular/glomerular/tubular/interstitial pathology

Post-renal:
- Obstruction

Question 12

Describe the pre-renal causes of AKI

Answer 12

This is majorly an issue of perfusion. Reduced perfusion reduces the GFR, and causes AKI. This usually responds well to volume replacement.

If left too long, it can cause irreversible ischaemic damage, becoming a renal AKI.

An example cause is renal artery stenosis and drugs (ACEi, ARBs, NSAIDs, calcineurin inhibitors, diuretics)

Question 13

Describe the renal causes of AKI

Answer 13

This can be a long range of causes from glomerular, to vascular, interstitial or tubular pathologies. Treatment will be based on the cause.

They can be caused by drugs, contrast, ischaemia, endogenous toxins or exogenous toxins.

Endogenous toxins:

• Myoglobin
• Immunoglobulins

Exogenous toxins:

• Aminoglycosides
• Amphotericin
• Acyclovir

Question 14

Describe post-renal causes of AKI

Answer 14

This is majorly caused by obstruction. Obstruction can be in the kidneys, ureters, bladder or urethra and then can intra or extra luminal. Treatment will be based on the pathology (e.g. stones or prostatic hypertrophy)

If left too long, it can lead to renal scarring, ischaemia and permanent renal impairment.

It can be seen on ultrasound.

Question 15

What are the indications for emergency dialysis in a case of AKI?

Answer 15

• Pulmonary oedema
• Refractory hyperkalaemia
• Metabolic acidosis
• Uraemic encephalopathy
• Drug toxicity

Question 16

What are the functions of the kidneys?

Answer 16

• Excretion of water soluble waste
• Water and electrolyte balance
• Acid base balance
• Hormone production (EPO, VitD, RAS)

Question 17

What are the main differences between acute kidney injury and chronic kidney disease?

Answer 17

AKI:

• Abrupt
• Sometimes reversible
• Treatment based on pathology

CKD:

• Chronic and long standing
• Irreversible
• Treatment is based on preventing worsening

Question 18

How do NSAIDs, calcineurin inhibitors, ACEi/ARBs and diuretics cause pre-renal AKI?

Answer 18

NSAIDs and calcineurin inhibitors: reduce afferent arteriole dilatation

ACEi/ARBs: reduce efferent arteriole constriction

Diuretics: tubular damage and reduces cardiac preload

Question 19

Define chronic kidney disease

Answer 19

A long-standing reduction in renal function, measured in stages.

Question 20

What are the stages of chronic kidney disease? What are the associated prevalence?

Answer 20

They are based on the GFR (ml/min)

Stage 1: <90 GFR
Stage 2: >60 GFR <89
Stage 3: >30 GFR <59
Stage 4: <15 GFR <29
Stage 5: <15 GFR

Most patients are in Stage 3, as Stage 1 and 2 are not diagnosed, and treatment keeps patients at stage 3.

Question 21

What are the most common causes of chronic kidney disease?

Answer 21

• Diabetes
• Atherosclerotic disease
• Hypertension
• Chronic glomerulonephritis
• Infective or obstructive uropathy
• Polycystic kidney disease

Question 22

What are the consequences of chronic kidney disease?

Answer 22

Failed homeostasis

• Metabolic acidosis
• Hyperkalaemia

Failed hormonal function

• Anaemia (reduced EPO)
• Bone disease (Reduced VitD)

Cardiovascular disease

• Vascular calcification and subsequent atherosclerosis
• Uraemic cardiomyopathy

Uraemia and death

Question 23

What is the main cause of death in patients with CKD?

Answer 23

Cardiovascular disease (calcification and atherosclerosis)

Question 24

Describe renal acidosis in patients with CKD

Answer 24

There is no hydrogen ion excretion so a build up causes acidosis. As an attempt to rectify, cells will pump out potassium and take in hydrogen, causing a hyperkalaemia.

Treat with oral bicarbonates

Question 25

What is the danger of high potassium?

Answer 25

Reduced cardiac and muscle function On ECG: flattened P waves, tall tented T waves

Question 26

Describe the bone disease in chronic kidney disease patients

Answer 26

Fibrotic changes to the bone, and reduced mineralisation can cause: - Osteotitis fibrosa - Osteomalacia

Question 27

What phosphate abnormality do CKD patients have, and how is this rectified?

Answer 27

They have a very high phosphate, which makes the body think there is a low calcium, so the parathyroid glands go into overdrive. To rectify: - Phosphate restricted diet and phosphate binders - Vitamin D analogues - PTH suppression (cinacalcet)