Chemical Pathology 14 - Acute and Chronic Renal failure 1 & 2 Flashcards
What is a normal GFR?
WHat is the age related decline in GFR?
120mls/ min
1ml/hour/year
What are the roles of the proximal and distal convoluted tubules?
Proximal: bulk resorption of glomerular filtrate
Distal: fine tuning of composition of filtrate
What is the gold-standard measure of GFR?
Inulin clearance
What is the most clinically-viable measure of GFR?
51Cr-EDTA and 99Tc-DTPA
How can plasma creatinine be used to estimate GFR?
Clearance = P(U x V) P = plasma concentration U = urinary concentration V = plasma volume
What would invalidate a creatinine-based measurement of GFR?
If function is not in a steady state
Why does plasma urea have a limited clinical value for measuring renal function?
Because it can be affected by many things so is highly variable
Describe the movement of creatinine from blood to urine
Freely filtered
Actively transported into urine by tubular cells
What equation can be used to refine your interpretation of creatinine clearance?
Cockcroft Gault Equation
What is the equation for estimated creatinine clearance?
((1.23 x (140- age) x weight))/ serum creatinine
Adjust by 0.85 if female
What is cystatin C, and why is it particularly useful?
Alternative to creatinine clearance
Largely unaffected by muscle mass/ gender/ age
In what condition does cystatin C not give a reliable result for GFR estimation?
Hypo/ hyperthyroidism
How can proteinuria be quantified?
Spot urine measurement
What can a 24-hour urine collection be used for?
- Creatinine clearance estimation
- Examination for stone-forming elements
- Proteinuria quantification (but this can also be done on spot urine testing)
- Electrolyte estimation (but this can also be done on spot urine testing)
What is the first choice of imaging in a suspected renal stone?
Abdo X ray
What is the first choice of imaging to assess renal blood flow?
USS with doppler
What is the first choice of imaging in investigating renal structural abnormalities?
CT
What options are available for functional imaging of the kidney?
Static and dynamic renograms
Recall the increases in creatinine that define each stage of AKI
Stage 1: 1.5-1.9 x the reference
Stage 2: 2-2.9 x the reference
Stage 3: >=3 x the reference (or >354)
Systematically recall some differentials for pre-renal AKI
Water loss: diuresis/ vomiting
Selective ischaemia: renal artery stenosis
Blood loss: road traffic accident/ drugs affecting renal blood flow
Oedematous states: heart failure
Recall 5 drug classes that can predispose to pre-renal AKI and the mechanism of each of these
NSAIDs - decrease afferent arteriolar dilatation
Calcineurin inhibitors - decrease afferent arteriolar dilatation
ACE inhibitors: decrease efferent constriction
ARBs: decrease efferent constriction
Diuretics: affect tubular function and pre-load
When does AKI become only partially reversible?
When acute tubulr necrosis occurs
Recall 3 differentials for the causes of post-renal AKI
It’s an obstructive pathology:
- Stone in renal pelvis
- Bilateral ureteric obstruction (BPH)
- Blocked urinary catheter
Systematically recall some causes of intrinsic renal AKI
Vascular causes (vasculitis/ vasculitides)
Glomerular (glomerulonephritis)
Tubular (ATN)
Interstitial (analgesic nephropathy)
Big proteins that clog up nephron - myoglobin (rhabdomyolysis), immunoglobin (amyloidosis, myeloma)
Toxins (contrast/ drugs)
What is the most common cause of intrinsic renal AKI?
Acute tubular necrosis
What are the 2 best measures of AKI severity?
Creatinine
Urine output
How is CKD stage 1 defined?
Kidney damage with normal GFR (>90)
How is CKD stage 5 defined?
End-stage - GFR <15
What is the best measure of prognosis in CKD?
Albumin creatinine ratio
What is the most common cause of CKD?
Diabetes by a long mile
How can CKD cause a failure of homeostatsis?
- Can cause acidosis due to reduced H+ excretion
- Can cause hyperkalaemia due to reduced K+ excretion
How can CKD cause a failure of hormonal function?
- Can lead to a normochromic normacytic anaemia due to failure of EPO production
- Can cause renal bone disease due to failure of PTH action
How can end-stage CKD affect the heart?
CKD –> less PTH action –> calcium elevated –> cardiac myocyte dysfunction –> uraemic cardiomyopathy
How should renal bone disease be treated (3 ways)?
- Phosphate control (phosphate binding drugs)
- Vitamin D receptor activators (eg 1 alpha calcidol) - this bypasses the need to synthesise vitamin D altogether
- PTH suppression (cinacalcet)
What is clearance?
When does clearance= GFR?
The volume of plasma that can be completely cleared of a marker substance ina. unit of time
Clearance=GFR if: marker is not bound to serum proteins, freely filtered by the glomeurlus and not secreted/reabsorbed by tubular cells
What is the gold standard measure of GFR?
Why si it not used widely?
inulin
*requires a steady state infusion and difficult to assay so it’s reserved for research purpses only*
What is used in clinical practice to measure GFR? How is it calculated?
Creatinine
*because the absolute levels vary so much, you measure the trend over time*
Equations: Cockcroft-Gault and MDRD - take account of diff combinations of age, weight, sex and ethnicity
What does urine specific gravity measure?
Concentration of solute
*higher urine specific gravity = higher solute concentration*
normal rage: 1.005-1.030
What does blood on urine dip signify?
Positive for blood: haematuria or myoglobinuria
Negative for blood: can reliably exclude haematuria
What has 24-hour urine collection been superceded by? *for the measurement of proteinuria*
Protein:creatinine ratio
For measurement of GFR is a single urine sample enough?
No- need to do 24 hour protein collection
What stones do you get in ethylene glycol poisoning?
Calcium oxalate stones
*because ethylene glycol consists of glycolic acid and oxalic acid; when oxalic acid combines wih calcium it forms calcium oxalate stones*
When would you see RBC on urine microscoy?
Stones or UTI
When would you see white blood cells on urine microscopy?
UTI or glomerulnephritis
When would you see casts on urine microscopy?
Glomeruloneprhitis
What is the definition of AKI?
Rise in serum creatinine over 26 within 48h
• A 50% or greater rise in serum creatinine known or presumed to have occurred
within the past 7 days • A fall in urine output to less than 0.5mL/kg/hour for more than 6 hours.
o Be wary that prostate and bladder pathology can cause this too
Indications for dialysis?
Acidosis (metabolic)
- Electrolyte disturbance e.g. refractory hyperkalaemia
- Intoxication e.g. lithium, aspirin
- Overload (fluid) e.g. pulmonary oedema
- Uraemic encephalopathy
(AEIOU)
How do you define end stage kidney failure?
GFR<15
Commonest causes of chornc kidney disease
Diabetes
• Atherosclerotic renal disease
• Hypertension
• Chronic Glomerulonephritis
• Infective or obstructive uropathy
• Polycystic kidney disease
Biggest mortality in CKD?
Vascular calcification and subsequent atheroscleorsiss
What are the 4 types of renal bone disease?
Osteitis fibrosa cystica: osteoclastic bone resorption
Osteomalacia: decreased bone mineralisation due to the low vitamin D
Adynamic bone disease: oversuppression of PTH
- this happens when you overtreat the hyperparathyroidism
Mixed renal osteodystrophy
Which iliac fossa is the transplanted kidney usually in?
Right iliac fossa
