Kidney Key Points Flashcards
What are the main plasma renal function tests?
Plasma creatinine
Urea
Urate
Sodium
Potassium
Write about low glomerular filtration rate
Elevated creatinine and urea indicate an issue with Glomerular filtration
A low glomerular filtration rate means waste products will build up in blood and there will be less of these products in the urine
5 marks on creatinine
Plasma creatinine concentration increases as GFR decreases, but it is not directly proportional to renal damage
Normal creatinine levels are proportional to muscle mass
Creatinine is a by-product of muscle metabolism
0% of creatinine should be absorbed by the kidneys, it should all be excreted
The change in a patient’s creatinine values are more of a concern then a stand alone high value
If plasma creatinine doubles, GFR has dropped by 50%
Increase in creatinine can be used to predict when intervention is required in end stage renal failure
Creatinine is used to calculate eGFR
5 marks on urea
A by-product of protein metabolism
High plasma indicates uraemia which is the build up of toxic chemicals due to the kidney’s becoming damaged and no longer being able to excrete the urea
Symptoms include nausea, vomiting, lethargy and confusion
40% of urea should be reabsorbed but the rest should be excreted
If tubular flow decreases due to renal hypoperfusion urea absorption will increase
Increased levels of urea indicate low GFR
Plasma ureamia may be caused by GI bleed, trauma, renal hypoperfusion, decreased extracellular fluid volume, acute renal impairment, chronic renal disease, post-renal obstruction such as calculus tumour
What causes urea increase in plasma?
GI bleed
Trauma
Renal hypoperfusion
Decreased extracellular fluid volume
Acute renal impairment
Chronic renal disease
Post-renal obstruction such as calculus tumour
5 marks on uric acid/urate
Formed by the breaking down of purines in the liver
Excreted in the urine and stool
A build up of urate forms urate crystals
Gout occurs when these urate crystals accumulate in your joints
This causes inflammation and pain
What is kidney disease
Two forms: acute kidney injury and chronic kidney disease
AKI - characterised by a reversible acute increase in nitrogen waste products measured through serum creatinine and urea or the kidneys inability to produce sufficient amount of urine over the course of hours to weeks.
CKD - low GFR. Divided into stages 1 to 5 depending on severity.
5 marks on acute kidney injury
A form of kidney disease
Characterised by a reversible acute increase in nitrogen waste products measured through serum creatinine and urea or the kidneys inability to produce sufficient amount of urine over the course of hours to weeks
Occurs because of damage to the kidney caused by decreased blood flow, exposure to substances harmful to the kidney, an inflammatory process in the kidney, or an obstruction of the urinary tract impeding flow
Can lead to metabolic acidosis, high potassium levels, uraemia, changes in blood fluid balance and death
Managed by treating the underlying cause of the condition
What causes acute kidney injury
Occurs because of damage to the kidney caused by decreased blood flow, exposure to substances harmful to the kidney, an inflammatory process in the kidney, or an obstruction of the urinary tract impeding flow
What can acute kidney injury lead to
Can lead to metabolic acidosis, high potassium levels, uraemia, changes in blood fluid balance and death
5 marks on Chronic kidney disease
A type of kidney disease
Grouped into stages depending on one’s GFR from stage 1 to stage 5
Stage 1 has a normal GFR but proteinuria
Stage 5 has a GFR below 15
Caused by damage over time e.g. glomerulonephritis, diabetes or high blood pressure
What causes proteinuria
Alteration of either pore size of negative charge on basement membrane of glomeruli causes loss of proteins such as albumin in the urine
10 marks on proteinuria
Loss > 0.15g/day almost always indicates disease
Three types of proteinuria occording to cause: functional, postural and nephrotic
Functional: seen in fever or exercise < 0.5g loss per day
Postural: seen in erect posture less than 1g loss a day
Nephrotic: loss > 3.5g/day
Three types according to type of loss: overflow, tubular, glomerular
Overflow - capacity to reabsorb protein from proximal tubule overwhelmed e.g. haemoglobinuria or myoglobinuria, Bence Jones proteinuria
Tubular - decreased tubular reabsorption of protein from proximal tubule < 2g daily e.g. Fanconi syndrome, tubulo-interstitial disease, acute renal insufficiency, chronic hypokalemia
Glomerular - nil disease and other glomerular diseases
How is proteinuria classified based on cause
Functional: seen in fever or exercise < 0.5g loss per day
Postural: seen in erect posture less than 1g loss a day
Nephrotic: loss > 3.5g/day
How is proteinuria classified based on cause
Three types according to type of loss: overflow, tubular, glomerular
Overflow - capacity to reabsorb protein from proximal tubule overwhelmed e.g. haemoglobinuria or myoglobinuria, Bence Jones proteinuria
Tubular - decreased tubular reabsorption of protein from proximal tubule < 2g daily e.g. Fanconi syndrome, tubulo-interstitial disease, acute renal insufficiency, chronic hypokalemia
Glomerular - nil disease and other glomerular diseases
What might cause overflow proteinuria?
(3)
Haemoglobinuria
Myoglobinuria
Bence Jones proteinuria
What might cause tubular proteinuria?
(4)
Fanconi syndrome
Tubulo-interstitial disease
Acute renal insufficiency
Chronic hypokalemia
What might cause glomerular proteinuria
Nil disease and other glomerular diseases
What four ways can urine be measured for protein
Screening test
24-hour protein excretion
Spot urine protein/creatinine ratio
24 hour urine collection for albumin or spot albumin to creatinine ratio if dip stick is negative
How is the proteinuria screening test carried out?
Allbustix
Impregnated paper strips
Does not detect light chains
Sulfosalicylic acid = white precipitate
How can the spot urine protein/creatinine ratio be used in proteinuria
Normal ratio of 0:1
Ration greater than 3.5 indicates nephrotic range proteinuria
What is postural proteinuria also called
Orthostatic proteinuria
Write about orthostatic proteinuria
(3)
More severe proteinuria in the upright prone position, may disappear at night
Commonest in adolescents and young adults
Often harmless but may be a sign of renal disease in the future
Write about microabluminuria
Normal excretion of albumin < 0.05 g/day.
DM patients who excrete more than this , but who have normal total protein excretion, are said to have microalbuminuria.
At risk of progressive renal disease unless there is stringent control of plasma glucose concentrations and blood pressure.
Write about tubular proteinuria
(3)
May be due to renal tubular damage from any cause [especially Pyelonephritis]
If glomerular permeability is normal, proteinuria < 1 g/day and consists of low molecular weight globulin’s [a - and b - globulin’s] a - and b - globulin’s are sensitive markers of renal tubular damage.
b 2 -microglobulins in urine are unstable so other proteins such as retinal binding protein are better indicators of tubular damage
Write about the presence of proteinuria but normal renal function, what might cause this?
Bence Jonnes Protein production
Severe haemolysis with haemoglobinuria
Severe muscle damage with myoglobinuria
5 marks on estimated glomerular filtration rate
GFR is the volume of filtrate produced by both kidneys each minute, approx 180L/day
GFR is difficult to measure directly so instead it’s measurement is based on the concept of clearance i.e. the determination of the volume of plasma from which a substance is removed by GF during its passage through the kidney
GFR can be measured using an IV infusion of inulin from garlic but this is difficult to assay
eGFR is calculated using equations based on serum creatinine as well as non-renal influences such as age, gender, race and body size
eGFR uses serum creatinine in its calculation as serum creatinine increases as GFR decreases
5 marks on GFR prediction equations
Modification of Diet in Renal Disease Study (MDRD) equation or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation are the most commonly used eGFR prediction equations.
These equations take into account a person’s serum creatinine levels and other non-renal factors such as age, gender, race and body size.
These equations are used to indirectly calculate the Glomerular Filtration Rate as this is a difficult to measure value.
To directly measure the GFR an IV infusion of inulin is given but this is difficult to assay.
The CKD-EPI is the better equation to use as it is shown to perform better than the MDRD equation especially at higher GFRs with less bias and greater accuracy
What are the two main eGFR equations used
Modification of Diet in Renal Disease Study (MDRD) equation
The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation
5 marks on urinalysis
Urinalysis investigates the appearance, specific gravity, osmolarity, pH, glucose, protein and urinary sediments found in a patient’s urine.
These are often measured using urinalysis dipsticks.
These sticks have up to 10 test areas and can semi-quantatively measure the components of urine.
These dipsticks usually measure urinary nitrites, pH, protein, glucose, ketones, urobilinogen, bilirubin, leukocytes and blood (haemoglobin).
High proteins in glucose could indicate kidney disease, bilirubin could indicate haemolysis, blood and leucocytes could indate infection, glucose could indicate diabetes mellitus as well as ketones, urinary nitrites measures creatinine and urea levels.
5 marks on creatinine clearance
0% of creatinine is reabsorbed in the kidneys, it is all excreted.
Creatinine levels increase in urine as GFR decreases, this can be used to predict the health of the glomeruli.
Creatinine clearance involves the subject collecting all their urine produced over 24 hours into a container, a portion of urine is used to measure the creatinine concentration (Ucreat).
A blood sample is also taken during the same 24 hours to determine the plasma creatine (Pcreat).
However many patients find this a difficult test to do as they often forget to gather all their samples, this has caused a variation of up to 20% to be seen.
The values recorded from the creatinine clearance test can be inputted into an equation to determine the health of your glomeruli.
Creatinine clearance is often used in an equation to determine eGFR such as the MDRD equation or the CKD-EPI equation to better estimate glomerular filtration rate
