Urea and Electrolytes

Question 1

What does a reddish serum indicate in a separated blood sample?

Answer 1

Haemolysis

Question 2

What are some physiological compensatory mechanisms for fluid loss?

Answer 2

• Thirst
• ADH
• RAAS system

Question 3

What are some therapeutic compensatory mechanisms for fluid loss?

Answer 3

• IV therapy
• Diuretics
• Dialysis

Question 4

What is ADH stimulated in response to?

Answer 4

Rise in concentration of osmotically active particles (osmolality)

Question 5

Since ADH analysis is not readily available how can it be measured?

Answer 5

• Measuring plasma and urine osmolality

- Urine > plasma suggests ADH is active

Question 6

What levels suggest the RAAS is active?

Answer 6

If urine Na+ is < 10 mmol/l

Question 7

What do plasma and urine levels of creatinine usually reflect?

Answer 7

Muscle mass

Question 8

What is elevated urea found in?

Answer 8

• CCF
• Shock
• MI
• Severe burns
• Gastric bleed

Question 9

How much urea enters the tubular lumen each day?

Answer 9

800 mmol (48g)

Question 10

What is the normal range of GFR?

Answer 10

90 - 150 ml/min

Question 11

What is GFR influenced by?

Answer 11

• Renal perfusion pressure
• Renal vascular resistance
• Glomerular damage
• Post-glomerular resistance

Question 12

What is the best overall measure of kidney function?

Answer 12

GFR

Question 13

What is eGFR used for?

Answer 13

Used to aid ‘staging’ of kidney disease

Question 14

What is an AKI flag used for/

Answer 14

Highlights subtle changes in renal function

Question 15

eGFR and AKI flag values are calculated based on what substance?

Answer 15

Creatinine

Question 16

What is hyponatraemia caused by?

Answer 16

• Too little Na in ECF (alcoholics usually)
• Excess water in ECF
• Pseudo hyponatraemia due to increased protein or lipid

Question 17

What is hypernatraemia caused by?

Answer 17

• Too little water in ECF

- Too much in ECF

Question 18

What is dehydration caused by?

Answer 18

• Water deficiency

- Fluid (Na and water) depletion

Question 19

What can hypovolaemia plus decreased urine sodium be due to?

Answer 19

• Vomitting
• Diarrhoea
• Skin loss

Question 20

What can hypovolaemia plus increased urine sodium be due to?

Answer 20

• Diuretics
• Addisons
• Na losing nephritis

Question 21

What can euvolemia plus normal plasma osmolarity be due to?

Answer 21

Pseudohyponatraemia

Question 22

What can euvolemia plus low plasma osmolarity plus increased urine Na+ be due to?

Answer 22

• SIADH
• Drugs
• CRF

Question 23

What can euvolemia plus low plasma osmolarity plus decreased urine Na+ be due to?

Answer 23

• Stress
• Post surgery
• Endocrine: Hypothyroid

Question 24

What can high plasma osmolarity and euvolemia be due to?

Answer 24

HYpertonic hyponatraemia

Question 25

What factors can affect plasma potassium?

Answer 25

• Acid-base status
• Insulin / glucose therapy
• Adrenaline
• Rapid cellular incorporation - TPN, leukaemia

Question 26

What is the effect of an acidosis oh K+?

Answer 26

Potassium moves out of cells (hyperkalaemia)

Question 27

What is the effect of an alkalosis on K+?

Answer 27

Potassium moves into cells (hypokalaemia)

Question 28

What can the causes of hyperkalaemia be?

Answer 28

Artefactual 
- Delay in sample analysis 
- Haemolysis 
- Drug therapy - excess intake 
Renal
- Acute + Chronic renal failure 
Acidosis (intracellular exchange)
Mineralocorticoid dysfunction 
- Adrenocortical failure 
- Mineralocorticoid resistance - e.g spironalactone 
Cell death 
- Cytotoxic therapy

Question 29

What are the causes of potassium depletion?

Answer 29

• Low intake
• Increased urine loss (diuretics, tubular dysfunction, mineralocorticoid excess)
• GI losses
• Hypokalaemia without depletion (alkalosis, insulin therapy)

Question 30

What can potassium depletion cause in the kidney?

Answer 30

• Polyuria

- Alkalosis - increase renal HCO3 production

Question 31

What could you possibly see in a history of someone with potassium depletion?

Answer 31

• Diarrhoea, vomitting, drugs (diuretics, digoxin)
• Symptoms of lethargy / weakness
• Cardiac arrythmias