Chemical Pathology - Renal Physiology Flashcards
(29 cards)
What is the normal glomerular filtration rate?
120ml/hr
What is the approximate age-related decline of renal function (GFR) per year?
1ml/hr/yr
What is renal clearance?
The volume of plasma that can be completely cleared of a marker substance in a unit of time
What is GFR (glomerular filtration rate)?
Clearance, if a marker is not bound to serum proteins, freely filtered by the glomerulus + not secreted/reabsorbed by tubular cells
What is the gold standard measure of GFR and what does it rely on?
Inulin
- Requires steady state infusion
What causes insensible water loss?
- High surface area
- High skin blood flow
- High metabolic/resp rate
- High transdermal fluid loss
What causes fluid overload?
- Bronchopulmonary dysplasia
- Necrotising enterocolitis
What causes hypernatraemia?
- Intraventricular haemorrhage
- Sodium bicarbonate when treating acidosis
What causes hyponatraemia?
- Congenital adrenal hyperplasia
- Caffeine/theophylline when treating apnoea
What type of marker is creatinine?
An endogenous marker
What is creatinine used for in clinical practice?
To measure renal function
How is creatinine used in clinical practice to measure renal function, and why?
- Monitor trend + use it to look for changes over time
- Very variable between individuals
What is creatinine a by-product of?
- Muscle turnover
= muscular individuals have higher creatinine than others
How is a single sample of urine examined?
- Dipstick testing
- Microscope examination
- Proteinuria quantification (PCR - protein:creatinine ratio)
How is a 24-hour collection of urine examined?
- Proteinuria quantification (superseded by PCR)
- Creatinine clearance estimation
- Electrolyte estimation
- Stone forming elements
What are the different elements observed on urine micropscopy and what do they signify?
- Crystals (stones)
- Red blood cells (stones, UTI)
- White blood cells (UTI, glomerulonephritis)
- Casts (glomerulonephritis)
- Bacteria (UTI)
What is an AKI defined as?
- Rise in serum creatinine >26 within 48hr
- 50% or great rise in serum creatinine known or presumed to have occurred within the past 7 days
- Fall in urine output to less than 0.5mL/kg/hr for more than 6hrs
What is an AKI defined as?
- Rise in serum creatinine >26 within 48hr
- 50% or great rise in serum creatinine known or presumed to have occurred within the past 7 days
- Fall in urine output to less than 0.5mL/kg/hr for more than 6hrs
What are pre-renal AKIs?
- Reduced renal perfusion with no structural abnormality of the kidney; can become renal if ischaemia leads to necrosis
- Responds to volume replacement
What are renal AKIs?
- Vascular, glomerular, tubular or interstitial
What are post-renal AKIs?
- Characterised by obstruction to urinary flow, glomerular filtration requires pressure gradient
- Reversal can lead to scarring + permanent renal impairment
What are 5 indications for dialysis?
AEIOU:
1. Acidosis
2. Electrolyte disturbance (e.g. refractory hyperkalaemia)
3. Intoxication (e.g. lithium, aspirin)
4. Overload (fluid) (e.g. pulmonary oedema)
5. Uraemic encephalopathy
What are the different stages of chronic kidney disease and their approximate GFRs?
- Kidney damage with normal GFR (>90)
- Mild GFR (60-89)
- Moderate GFR (30-59)
- Severe GFR (15-29)
- End-stage kidney failure (<15 or dialysis)
What are the commonest causes of chronic kidney disease?
- Diabetes
- Atherosclerotic renal disease
- Hypertension
- Chronic Glomerulonephritis
- Infective or obstructive uropathy
- Polycystic kidney disease
