Renal

Question 1

What is cystatin C?

Answer 1

• Endogenous cysteine proteinase inhibitor that is produced at a constant rate by all nucleated cells and released into plasma
• 99% filtered by glomeruli
• NO tubular secretion or reabsorption into plasma
• After filtration it is completely absorbed into proximal tubular cells and catabolised
• Usually none found in urine
• Therefore
o Plasma cystatin C is a good marker of GFR
o Urine cystatin C might be a good marker of tubular injury
• Evidence: in a systemic review
o Serum cystatin C 84% sensitive for AKI, 82% specific, AUC 0.96
o Performed better than Cr in estimating GFR in some circumstances (e.g. low muscle mass)

Question 2

What is NGAL (neutrophil gelatinase associated lipocalin)?

Answer 2

• Originally found bound to gelatinase from human neutrophils
• Possibly a bacteriostatic protein that scavenges bacterial iron containing proteins, other possible roles
• Expression upregulated following ischaemia in renal proximal epithelial cells, possibly to ameliorate oxidatve stress
o Increased NGAL in urine is from renal tubular cells
• Urine NGAL found to
o Predict development of AKI in critically ill patients (i.e. gives early diagnosis of AKI)
o Predict sustained AKI
• Meta-analysis showed (in critically ill patients)
o Diagnostic odds ratio = 10
o AUC = 0.73

Question 3

Other than fluids, what has been shown to reduce risk of contrast-induced AKI?

Answer 3

1. IV hydration = most important intervention to reduce risk of CI-AKI in at-risk patients
2. Low contrast volume
3. Non-ionic contrast (low or iso-osmolar)
4. NAC - heterogeneous results; KDIGO does recommend using oral NAC + IV N Saline in patients at increased risk
5. Statins - several RCTs support protective effects of statins (possibly through effects on inflammation/endothelium)

Question 4

Risk of rhabdomyolysis is usually low when CK is less than…

Answer 4

CK <15,000 to 20,000

Question 5

List some drugs that cause acute tubular necrosis

Answer 5

Aminoglycosides 
Vancomycin 
Amphotericin 
Contrast
Cisplatin 
Cyslosporin, tacrolimus 
Foscarnet

Question 6

What is the most common cause of acute tubulointerstitial nephritis (RACP 2018 AKI lecture)?

Answer 6

Proton pump inhibitors

Question 7

What is the definition of AKI using the KDIGO criteria?

Answer 7

AKI is defined as any of the following
• Increase in serum Cr >=0.3 mg/dL (>=26.5 umol/L) within 48 hours
• Increase in serum Cr to >=1.5x baseline, which is known or presumed to have occurred within prior 7 days
• Urine volume <0.5 mL/kg/hour for 6 hours

Staging
Stage 1. Serum Cr 1.5-1.9x baseline OR >=26.5 umol/L increase, OR urine output <0.5mL/kg/h for 6-12 hours
Stage 2. Serum Cr 2-2.9x baseline OR UO <0.5mL/kg/h for >=12h
Stage 3. Serum Cr 3x baseline OR increase by >=353.6 umol/L OR initiation of RRT OR eGFR <35 in patients aged <18. OR UO <0.3mL/kg/h for >=24h OR anuria for >=12h