Urea + Electroylte Tests

Question 1

Which components are typically filtered by the kidneys?

Answer 1

• Low molecular weight (LMW) components are filtered by the kidneys.

Question 2

What is the normal glomerular filtration rate (GFR) in humans?

Answer 2

• The normal GFR is approximately 120 mL/min.

Question 3

What is the typical range of urine production in a 24-hour period?

Answer 3

• Normal urine production is between 1–2 liters per day

Question 4

Why is glomerular filtration rate (GFR) important?

Answer 4

• GFR is a key indicator of overall health and is particularly important for assessing kidney function and drug excretion.

Question 5

Which substance is commonly used as a proxy marker for GFR?

Answer 5

• Creatinine is used as a proxy marker for GFR because it is completely filtered by the kidneys and not reabsorbed.

Question 6

What is creatinine?

Answer 6

• Creatinine is a waste product formed from the normal breakdown of creatine, a compound essential for muscle energy metabolism

Question 7

How is creatinine eliminated from the body?

Answer 7

• Creatinine is filtered out of the blood by the kidneys and excreted in urine.

Question 8

Why does muscle mass affect creatinine levels?

Answer 8

• Muscle mass affects creatinine levels because creatinine production is proportional to muscle metabolism, meaning individuals with more muscle mass produce more creatinine

Question 9

What happens to the majority of creatinine in the kidneys?

Answer 9

• About 90–95% of creatinine is filtered through the glomerulus.

Question 10

What happens to the remaining 5–10% of creatinine in the kidneys?

Answer 10

• the remaining 5–10% of creatinine is secreted into the urine by the cells of the distal tubule.

Question 11

What is the Cockcroft-Gault equation used for?

Answer 11

• The Cockcroft-Gault equation is used to estimate creatinine clearance (CrCl), which reflects kidney function.

Question 12

What is the Cockcroft-Gault equation ?

Answer 12

• CrCl (mL/min) = (140-age) x weight x (1.23 male/1.04 female) / SrCr (μmol/L)

Question 13

What creatinine clearance (CrCl) ranges correspond to kidney impairment?

Answer 13

• 50–20 mL/min: Mild impairment
• 20–10 mL/min: Moderate impairment
• <10 mL/min: Severe impairment

Question 14

Why is creatinine clearance (CrCl) inherently inaccurate?

Answer 14

• CrCl slightly overestimates GFR because a small amount of creatinine is secreted by the renal tubules
• its accuracy is influenced by various patient factors.

Question 15

In which patients is CrCl particularly inaccurate?

Answer 15

• Patients with significant muscle wastage.
• Patients with low muscle mass.
• Cachexic (severely malnourished) patients.
• Patients with rapidly changing serum creatinine levels.

Question 16

What is acute kidney injury (AKI)?

Answer 16

• AKI is a sudden decline in kidney function, characterized by reduced glomerular filtration rate (GFR)
• impaired fluid and electrolyte balance, and accumulation of waste products in the blood.

Question 17

What are the primary causes of AKI?

Answer 17

1. Pre-renal: Reduced blood flow to the kidneys (e.g., dehydration, hypotension).
   
   2. Intrinsic: Direct damage to kidney tissues (e.g., acute tubular necrosis, glomerulonephritis).
   3. Post-renal: Obstruction of urine outflow (e.g., kidney stones, enlarged prostate).

Question 18

How is urea produced ?

Answer 18

• in the liver
• after the delaminating of amino acids

Question 19

How is urea cleared form the body ?

Answer 19

• by the golmerular filtration
• it is a major source of N loss from the body

Question 20

Is urea reabsorbed in the body ?

Answer 20

• some urea is reabsorbed by passive tubular reabsorption

Question 21

What does high level of urea indicate ?

Answer 21

• dehydration
• gastric blood loss
• infection

Question 22

What does low level of urea indicate ?

Answer 22

• oedema
• pregnancy
• low protein diet

Question 23

Where is potassium primarily found in the body?

Answer 23

• Potassium is primarily an intracellular cation, meaning most of it is found inside cells.

Question 24

Why are serum potassium (K+) levels important?

Answer 24

• Serum K+ levels are crucial because they influence membrane potential and can cause rapid changes in cell function, particularly in nerve and muscle cells.

Question 25

What percentage of potassium is available for exchange in the body?

Answer 25

- About 90% of the total body potassium is available for exchange.

Question 26

Where is the remaining 10% of potassium in the body found?

Answer 26

- the remaining 10% of potassium is bound in red blood cells (RBCs) and other tissues.

Question 27

How are potassium and sodium movements related in the kidneys?

Answer 27

- K and Na movements are closely related because as Na is actively reabsorbed, K moves into the filtrate to maintain membrane potential balance.

Question 28

How do hydrogen ions (H+) move in relation to potassium in the kidneys?

Answer 28

- H+ ions tend to move with potassium in the renal tubules - but this depends on the ability of the tubular cells to secrete H+.

Question 29

What happens to potassium levels in acidosis?

Answer 29

- hyperkalemia (high potassium) - because hydrogen ions shift into cells, and potassium shifts out to maintain charge balance.

Question 30

What happens to potassium levels in alkalosis?

Answer 30

- hypokalemia (low potassium) - hydrogen ions shift out of cells, and potassium moves into cells to maintain balance - less in bloodstream

Question 31

What is the normal range for potassium in the body ?

Answer 31

3.6 - 5.2 mmol/L

Question 32

What happens when the water content of the blood is low?

Answer 32

- blood water content is low (due to too much salt or sweating) - brain produces more ADH, causing the kidneys to reabsorb more water - resulting in low urine output / less water in urine (small volume of concentrated urine).

Question 33

What happens when the water content of the blood is high?

Answer 33

- blood water content is high (due to drinking too much water) - the brain produces less ADH - leading to low reabsorption of water by the kidneys and high urine output (large volume of dilute urine).

Question 34

What is the definition of hyponatremia?

Answer 34

- serum sodium concentration of less than 135 mmol/L. - Treatment is typically required when serum sodium is below 120 mmol/L.

Question 35

What is the most common cause of hyponatremia?

Answer 35

- rarely due to low sodium intake but is usually caused by defective homeostatic mechanisms - such as the inability to properly regulate water and sodium balance.

Question 36

What is the underlying issue in most cases of hyponatremia?

Answer 36

- often an excess of water relative to sodium, meaning there is more water than sodium in extracellular fluid

Question 37

What is required to develop hyponatraemia ?

Answer 37

- Source of free water • Impaired ability of the urine to excrete dilute urine. • Reduced solute intake • Poor renal function

Question 38

What are symptoms of people with hyponatraemia ?

Answer 38

- Cerebral edema • Confusion • Seizures • Coma • Brain herniation (in severe cases)

Question 39

What is hypernatraemia ?

Answer 39

- marked decrease in water relative to sodium. • Does not occur unless there is impaired thirst mechanisms or lack of access to water • Can be cause by drugs or (usually) by drinking sea water

Question 40

What is the role of glomerular filtration in protein loss?

Answer 40

- the glomerular filtration system is designed to filter out large molecules, such as proteins, and prevent them from crossing into the filtrate.

Question 41

What is the normal range for protein loss in the urine?

Answer 41

- A protein loss of <150 mg/day is considered normal.

Question 42

What is microalbuminuria?

Answer 42

- Microalbuminuria refers to the loss of albumin in the urine at levels of >30 mg/L.