Clinical pathology of renal disease

Question 1

What are the functions of the kidney? And which one are affected first by AKI and CKD?

Answer 1

Excretion and homeostasis –> Waste products, acid-base balance, etc

Endocrine functions –> RAAS, erythopoietin production, hydroxylation of vitamin D

E&H are damaged early in AKI and late in CKD, while Endocrine functions are damaged in CKD.

Question 2

What are the causes of renal AKI?

Answer 2

1) Renal underpefusion
2) Intrinsic renal damage
3) Obstruction

Question 3

What can causes renal underperfusion?

Answer 3

1) Hypovolaemia –> Haemorrhage, Dehydration (elderly, postsurgery)
2) Sepsis (vasodilatation)
3) Renal artery stenosis /atherosclerosis
4) Pump failure (heart)

Question 4

What can cause intrinsic renal damage?

Answer 4

1) Ischaemia
2) Nephrotoxins–> Drugs, poisons, myoglobin (rhabdomyolysis), paraproteins (myeloma)
3) Infection (pyelonephritis)
4) Trauma

5) Early stage of inflammatory causes of chronic kidney
disease (glomerulonephritis, interstitial nephritis)

Question 5

What are the causes of renal obstruction?

Answer 5

1) Stones
2) Tumour
3) Prostatic hypertrophy (most common)

Question 6

How would sodium be effected in a pre-renal uraemia and in intrinsic renal damage?

Answer 6

1) Pre-renal uraemia
- -> Urine sodium is <15
- -> Serum sodium is HIGH (helps to preserve water)

2) Intrinsic renal damage
- -> Urine sodium is >40
- -> Serum sodium is LOW (kidney stopped working)

Question 7

When should fluids be given in AKI?

Answer 7

Fluid cures in the pre-renal uraemia state.
–> Fluid resolves low GFR from low renal perfusion.

Fluid kills in the intrinsic renal damage stage.

Question 8

What biochemical changes occur in AKI?

Answer 8

Hyperkalaemia –> Retain potassium to help neutralise acid pH (metabolic acidosis).

Life threatening when….

1) Plasma pH <7.0
2) Potassium > 8mmol/l

Retain nitrogenous waste products.

Hyponatraemia –> First sign of fluid retention –> Will eventually lead to fluid overload.

REMEMBER you do not see endocrine changes in AKI.

Question 9

What drugs should you avoid in AKI?

Answer 9

ACE inhibitors
ARBs
NSAIDs
And other nephrotoxic drugs

Question 10

What are some causes of CKD?

Answer 10

Diabetes Mellitus, Hypertension
Polycystic Kidney Disease
Recurrent pyelonephritis / reflux nephropathy
Glomerulonephritis
Interstitial nephritis
Multisystem disease
Drugs

Question 11

What tests do you use to monitor early and late CKD?

Answer 11

EARLY –> eGFR

LATE –> Serum creatinine

Question 12

What are the ranges for albumin to creatinine ratio (ACR) in CKD?

Answer 12

A1 <3

A2 3-30

A3 >30

Question 13

What biochemical changes occur in CKD stage 3-4?

Answer 13

1) Elevated creatinine, reduced eGFr, Elevated ACR

2) Endocrine changes
- -> Reduced 1alpha hydroxylation of Vitamin D
- -> Hypocalcaemia and secondary hyperparathyroidism
- -> Reduced Erythropoietin, causing anaemia

3) Lipids –> Elevated Cholesterol & Triglyceride partly accounts for increased risk of CHD
4) Impaired immune function

Question 14

What biochemical changes occur in CKD stage 4-5?

Answer 14

1) Elevated creatinine AND urea
2) High phosphate
3) Acidosis
4) Hyperkalaemia –> offset by increased gut losses until late stage

Question 15

Most patients with CKD do NOT get oliguria until very late stage, except when the cause of the CKD is….

Answer 15

Glomerular damage (EG: glomerulonephritis)

Question 16

How does lack of vitamin D cause bone damage?

Osteomalacia and osteitis fibrosa

Answer 16

Vit D is unable to absorb calcium in the gut so plasma calcium decreases.
Therefore parathyroid hormone increases to absorb calcium from bone.

Also metabolic acidosis causes bone buffers to be dissolved –> osteoporosis (from reduced GFR)

Also get increased plasma phosphate which binds to calcium –> Metastatic calcifications

Question 17

What are the two main causes of hypokalaemic acidosis?

Answer 17

1) GI loss –> diarrhoea, laxatives

2) Renal tubular acidosis –> renal loss of potassium