Kidney disease - the basics

Question 1

What are the functions of the kidney?

Answer 1

• Metabolic waste excretion
• Control of solutes and fluid status
• Endocrine functions
• Blood pressure control
• Acid/base balance
• Drug metabolism/excretion

Question 2

What is the primary role of the kidneys?

Answer 2

maintain fluid and electrolyte homeostasis in response to blood pressure and hormones

Question 3

How can we measure metabolic waste excretion

Answer 3

Measure urea and creatinine

Question 4

How can we measure the control of solute and fluid status

Answer 4

Measure sodium and potassium

Question 5

What are the endocrine functions of the kidneys?

Answer 5

• vitamin D
• EPO - erythropoietin
• PTH - parathyroid hormone

Question 6

What are the U and Es?

Answer 6

• Sodium
• Potassium
• chloride
• Urea
• creatinine
• eGFR
• Sometimes bicarbonate

Question 7

What are the characteristics of a substance used to measure kidney function?

Answer 7

• Freely filtered at the glomerulus
• Not secreted
• Not reabsorbed

Question 8

What are the causes of an abnormal serum urea?

Answer 8

• Diet: high protein or GI bleed
• Dehydration: passive reabsorption in the proximal tubule
• Tissue breakdown e.g. corticosteroid
• Liver failure lowers urea
• Up to 40% reabsorption

Question 9

What is renal clearance?

Answer 9

Volume of plasma which would be cleared of the substance per unit time

Question 10

What is the best measure of renal clearance?

Answer 10

Inulin

Question 11

What is the MDRD formula based on?

Answer 11

• Plasma creatinine concentration
• Age (adults only)
• Gender

Question 12

How is the value of eGFR expressed when using the MDRD formula?

Answer 12

ml/min per 1.73m^2 body surface area

Question 13

What is measured to calculate eGFR?

Answer 13

Plasma creatinine

Question 14

When is it not suitable to use eGFR?

Answer 14

• Acute kidney injury

* When renal function is unstable

Question 15

Describe stage 1 of chronic kidney disease

Answer 15

• eGFR >/90ml/min

* Need to have another abnormality otherwise regarded as normal

Question 16

Describe stage 2 of chronic kidney disease

Answer 16

• eGFR 60-89ml/min

* needs to have another abnormality otherwise regarded as normal

Question 17

Describe stage 3 of chronic kidney disease

Answer 17

• eGFR 30-59

* Moderate impairment

Question 18

Describe stage 4 of chronic kidney disease

Answer 18

• eGFR: 15-29

* Severe impairment

Question 19

Describe stage 5 of chronic kidney disease

Answer 19

• eGFR <15

* Advanced renal failure

Question 20

What are the normal proportions of proteinuria?

Answer 20

• Albumin 15%

* Other proteins 85% e.g. Tamm Horsfall, immunoglobulin

Question 21

What proteins does urinalysis detect?

Answer 21

Albumin only

Question 22

What is the detection of protein in the urine dependent on?

Answer 22

The concentration of the urine, if it is very concentrated it will look like there is a lot more protein in the urine than there actually is so don’t depend on dipstick alone

Question 23

How do you measure urinary protein excretion?

Answer 23

• 24 hour urine collection
• Protein:creatinine ratio (PCR) on morning spot sample
• Albumin:creatinine ration

Question 24

Describe the balance of protein in proteinuria

Answer 24

• 70% albumin

* 30% other proteins

Question 25

What is the classification of microalbuminuria?

Answer 25

Male: 2.5-25 mg/mmol
female: 3.5-35 mg/mmol

Question 26

What is the classification of macroalbuminuria?

Answer 26

Male >25mg/mmol

Female >35 mg/mmol