Kidney Key Points

Question 1

What are the main plasma renal function tests?

Answer 1

Plasma creatinine
Urea
Urate
Sodium
Potassium

Question 2

Write about low glomerular filtration rate

Answer 2

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

Question 3

5 marks on creatinine

Answer 3

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

Question 4

5 marks on urea

Answer 4

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

Question 5

What causes urea increase in plasma?

Answer 5

GI bleed
Trauma
Renal hypoperfusion
Decreased extracellular fluid volume
Acute renal impairment
Chronic renal disease
Post-renal obstruction such as calculus tumour

Question 6

5 marks on uric acid/urate

Answer 6

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

Question 7

What is kidney disease

Answer 7

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.

Question 8

5 marks on acute kidney injury

Answer 8

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

Question 9

What causes acute kidney injury

Answer 9

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

Question 10

What can acute kidney injury lead to

Answer 10

Can lead to metabolic acidosis, high potassium levels, uraemia, changes in blood fluid balance and death

Question 11

5 marks on Chronic kidney disease

Answer 11

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

Question 12

What causes proteinuria

Answer 12

Alteration of either pore size of negative charge on basement membrane of glomeruli causes loss of proteins such as albumin in the urine

Question 13

10 marks on proteinuria

Answer 13

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

Question 14

How is proteinuria classified based on cause

Answer 14

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

Question 15

How is proteinuria classified based on cause

Answer 15

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

Question 16

What might cause overflow proteinuria?
(3)

Answer 16

Haemoglobinuria
Myoglobinuria
Bence Jones proteinuria

Question 17

What might cause tubular proteinuria?
(4)

Answer 17

Fanconi syndrome
Tubulo-interstitial disease
Acute renal insufficiency
Chronic hypokalemia

Question 18

What might cause glomerular proteinuria

Answer 18

Nil disease and other glomerular diseases

Question 19

What four ways can urine be measured for protein

Answer 19

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

Question 20

How is the proteinuria screening test carried out?

Answer 20

Allbustix
Impregnated paper strips
Does not detect light chains
Sulfosalicylic acid = white precipitate

Question 21

How can the spot urine protein/creatinine ratio be used in proteinuria

Answer 21

Normal ratio of 0:1
Ration greater than 3.5 indicates nephrotic range proteinuria

Question 22

What is postural proteinuria also called

Answer 22

Orthostatic proteinuria

Question 23

Write about orthostatic proteinuria
(3)

Answer 23

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

Question 24

Write about microabluminuria

Answer 24

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.

Question 25

Write about tubular proteinuria
(3)

Answer 25

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

Question 26

Write about the presence of proteinuria but normal renal function, what might cause this?

Answer 26

Bence Jonnes Protein production

Severe haemolysis with haemoglobinuria

Severe muscle damage with myoglobinuria

Question 27

5 marks on estimated glomerular filtration rate

Answer 27

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

Question 28

5 marks on GFR prediction equations

Answer 28

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

Question 29

What are the two main eGFR equations used

Answer 29

Modification of Diet in Renal Disease Study (MDRD) equation

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation

Question 30

5 marks on urinalysis

Answer 30

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.

Question 31

5 marks on creatinine clearance

Answer 31

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