Measurement of kidney function

Question 1

What are the three basic processes that occur in the nephron?

Answer 1

Filtration, reabsorption, and secretion.

Question 2

What substances are filtered during the process of filtration in the nephron?

Answer 2

Blood cells, proteins, and the ultrafiltrate of plasma.

Question 3

What substances are reabsorbed in the nephron?

Answer 3

Electrolytes, solutes, and water.

Question 4

What substances are secreted in the nephron?

Answer 4

Hydrogen ions, potassium, and drugs.

Question 5

What is the definition of renal clearance?

Answer 5

Renal clearance is the volume of plasma completely cleared of a given substance in unit time (measured in mL/min).

Question 6

What does renal clearance measure and provide information about?

Answer 6

Renal clearance measures excretion and provides summary information about glomerular filtration, tubular reabsorption, and tubular secretion.

Question 7

What is the glomerular filtration rate (GFR)?

Answer 7

The glomerular filtration rate is the rate at which fluid is filtered at the glomerulus, measured in mL/min.

Question 8

How does GFR differ from clearance?

Answer 8

GFR measures glomerular function only, while clearance provides information about both filtration and reabsorption.

Question 9

What substances are involved in both filtration and clearance?

Answer 9

Filtration includes blood cells, proteins, and the ultrafiltrate of plasma, while clearance includes GFR.

Question 10

Which process is responsible for the excretion of urine?

Answer 10

Excretion is the final step and results in the formation of urine.

Question 11

What factors determine the glomerular filtration rate (GFR)?

Answer 11

Filtration pressures, charge of molecules, and size of molecules.

Question 12

How does renal blood flow affect GFR?

Answer 12

Renal blood flow plays a role in controlling GFR by influencing the filtration pressures in the glomerulus.

Question 13

What is the role of the macula densa in controlling GFR?

Answer 13

The macula densa, located in the distal convoluted tubule, senses changes in sodium concentration and controls GFR through the tubuloglomerular feedback mechanism.

Question 14

How is GFR assessed in a clinical setting?

Answer 14

GFR can be assessed through serum biochemistry, measurement of clearance, and calculated clearance using methods such as renography.

Question 15

What are the principles of clearance?

Answer 15

Clearance is determined by the filtration and reabsorption of substances. Inulin is freely filtered and not reabsorbed, para-aminohippurate is filtered and partially reabsorbed, and certain substances like amino acids are filtered and completely reabsorbed.

Question 16

What is inulin clearance?

Answer 16

Inulin clearance is a measure of the virtual volume of blood that would be completely cleared of inulin in a given time. It is calculated using the formula: Inulin Clearance = (UInulin x Vurine) / PInulin.

Question 17

What is a drawback of using inulin clearance?

Answer 17

Inulin clearance requires infusion of inulin to maintain a constant plasma concentration, measurement of inulin concentration in blood samples, timed urine collection, and accurate measurement of urine volumes, making it cumbersome for routine clinical use.

Question 18

What does the volume of urine formed in a given time represent?

Answer 18

The volume of urine formed in a given time reflects the excretory function of the kidneys.

Question 19

What is creatinine?

Answer 19

Creatinine is a breakdown product of creatine phosphate in muscle.

Question 20

How is creatinine generally produced in the body?

Answer 20

Creatinine is generally produced at a constant rate in the body.

Question 21

How is creatinine handled in the kidneys?

Answer 21

Creatinine is filtered at the glomerulus and some of it is also secreted into the proximal tubule.

Question 22

What factors can alter creatinine levels?

Answer 22

Large muscle mass, cachexia, pregnancy, liver disease, and certain drugs such as cimetidine and trimethoprim can alter creatinine levels.

Question 23

Can changes in creatinine levels accurately reflect kidney function?

Answer 23

Yes, large changes in creatinine levels can indicate kidney dysfunction even when there is little change in glomerular filtration rate (GFR).

Question 24

Can changes in GFR be reflected in creatinine levels?

Answer 24

In later stages of renal disease, there can be significant changes in creatinine levels even when there is little change in GFR.

Question 25

What is creatinine clearance?

Answer 25

Creatinine clearance is the virtual volume of blood that would be completely cleared of creatinine in a given time, measured in mL/min.

Question 26

How is creatinine clearance calculated?

Answer 26

Creatinine clearance is calculated using the formula: Creatinine Clearance = (Ucreat x Vurine) / Pcreat.

Question 27

What is a drawback of using creatinine clearance?

Answer 27

Inaccurate measurement of urine volumes can introduce large errors. Additionally, creatinine clearance does not provide information about the proportion of creatinine that is filtered versus secreted. It also tends to overestimate glomerular filtration rate (GFR) at low levels of GFR.

Question 28

How can clearance be estimated using plasma creatinine?

Answer 28

The Cockcroft-Gault, MDRD, and CKD-EPI formulas are commonly used to estimate GFR based on plasma creatinine levels, age, and other factors.

Question 29

What is renography, and how is it used to estimate clearance?

Answer 29

Renography involves injecting a radioactive tracer and measuring its concentration in the blood over time. It is considered the most accurate method for estimating GFR, but it is expensive and requires specialized equipment.

Question 30

What do U&E and RFT stand for in blood tests?

Answer 30

U&E stands for Urea and Electrolytes, while RFT stands for Renal Function Tests.

Question 31

What is the purpose of arterial blood gases (ABG) test?

Answer 31

Arterial blood gases are used to assess the oxygen and carbon dioxide levels, as well as the acidity (pH) and bicarbonate levels in the blood.

Question 32

What does a urinalysis involve?

Answer 32

Urinalysis is the examination of urine to assess various components such as pH, specific gravity, presence of proteins, glucose, blood cells, and bacteria.

Question 33

Why is renal function important?

Answer 33

Renal function is important for the identification of renal disease, maintenance of homeostasis, elimination of drugs by the kidney, fluid balance, blood pressure control, acid-base balance, and prevention of cardiovascular disease and sepsis.

Question 34

What are the common causes of kidney dysfunction?

Answer 34

Kidney dysfunction can be categorized as pre-renal (e.g., sepsis, heart failure), renal (e.g., glomerulonephritis, diabetic nephropathy), or post-renal (e.g., kidney stones, ureteric obstruction).

Question 35

What are the symptoms of kidney dysfunction?

Answer 35

Symptoms of kidney dysfunction may include lethargy/fatigue, nausea/vomiting, anorexia, confusion, oliguria, anuria, haematuria, itching, and a relevant drug history.

Question 36

What are the signs and observations indicating kidney dysfunction?

Answer 36

Signs may include rash, edema, palpable bladder, while observations may involve fluid status, weight changes, low urine output (oliguria), absence of urine output (anuria), and low or high blood pressure.

Question 37

What investigations are used to diagnose kidney dysfunction?

Answer 37

Diagnostic investigations include serum creatinine, estimated glomerular filtration rate (eGFR), potassium levels, ECG, blood gases, urinalysis, urinary albumin/creatinine ratio, and imaging such as CT or ultrasound (USS).

Question 38

How is kidney function monitored?

Answer 38

Monitoring of kidney function involves regular assessment of pulse/blood pressure, urine output, daily weight, blood tests (including potassium and creatinine levels), blood gases (pH and lactate), urine tests (albumin/creatinine ratio), and other relevant investigations.

Question 39

What is the role of the kidney in acid-base balance?

Answer 39

The kidney helps regulate the acid-base balance in the body.

Question 40

What is the role of the kidney in water balance?

Answer 40

The kidney helps maintain water balance by regulating water reabsorption and excretion.

Question 41

What is the role of the kidney in electrolyte balance?

Answer 41

The kidney helps regulate the levels of electrolytes such as sodium, potassium, calcium, and phosphate in the body.

Question 42

What is the role of the kidney in toxin and waste product removal?

Answer 42

The kidney filters and removes waste products, toxins, and excess substances from the blood, which are then excreted in the urine.

Question 43

What is the role of the kidney in blood pressure control?

Answer 43

The kidney helps regulate blood pressure by adjusting the volume of blood and the balance of sodium and water in the body.

Question 44

What is the role of the kidney in erythropoietin production?

Answer 44

The kidney produces erythropoietin, a hormone that stimulates the production of red blood cells in the bone marrow.

Question 45

What is the role of the kidney in vitamin D activation?

Answer 45

The kidney plays a crucial role in converting inactive vitamin D into its active form, which is important for calcium homeostasis and bone health

Question 46

What are some potential signs or symptoms of kidney dysfunction?

Answer 46

Oedema (swelling), high blood pressure, anemia, low serum calcium, acidosis, fluid overload, and drug toxicity may indicate kidney dysfunction.

Question 47

What are some tests or measurements used to assess kidney function?

Answer 47

Blood gases, serum renal function tests (RFTs), clearance measurements, hemoglobin (Hb) levels, blood calcium levels, blood pressure monitoring, weight measurement, and urine output monitoring are used to evaluate kidney function.