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ipfc 1 midterm 1 > Clinical Biochem 3 > Flashcards

Clinical Biochem 3 Flashcards

1
Q

Why do we check renal function? What is the kidney responsible for?

A
  • clearing waste material from blood
  • Maintain salt/water balance
  • Regulate blood pressure
  • Stimulate bone marrow to make RBCs
  • Control Ca/Phos absorption and secretion
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2
Q

Differentiate between hemodialysis and peritoneal dialysis

A

Hemodialysis
- blood is cleaned outside the body with a machine

Peritoneal dialysis
- blood is cleaned inside the body
- Dialysis fluid is added to abdominal cavity using catheter
- toxins and water are absorbed by the fluid, dirty fluid is replaced by clean fluid

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3
Q

What 2 renal function tests (natural vs non-natural) can be used to estimate GFR. give examples

A

Exogenous (not natural) substances administed
- eg. Inulin, iothalamte and radioactive substances

Endogenous (natural) substances are measured in the body and used as surrogate markers of GFR
- eg. Blood Urea Nitrogen (BUN), Serum Creatinine (SCr)

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4
Q

Describe Inulin

A
  • It is not metabolized, secreted, reabsorbed or protein bound therefore = 100% is cleared from kidney = true measure of GFR
  • Gold standard for measure of GFR but is invasive and requires specialized tools (research only)
  • calculate inulin clearance by measuring plasma and urine inulin conc. and urine flow
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4
Q

What is BUN (blood urea nitrogen) used for? Reference range?

A

2.5-8 mmol/L
Non-specific screening/monitoring tool
- To assess hydration, renal function, protein tolerance, catabolism

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4
Q

Describe Iothalamte and Radioactive Substances

A
  • Invasive: requires injectin of foreigh substances, frequent blood sampling, and timed urine collection
  • research tool only
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5
Q

Why is BUN not as accurate as inulin or radioactive markers

A

Urea undergoes some tubular reabsoportion

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6
Q

What does a decreased BUN indicate? What does it not indicate?

A
  • indicate malnourishment
  • may be associated with liver disease

NOT CAUSED BY renal dysfunction
(no pathological consequence)

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7
Q

What are the 3 causes associated with elevated BUN

A

Pre-renal causes
Intra-renal causes
Post-renal causes

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8
Q

Explain Pre-renal causes that elevate BUN (2)

A
  1. Decreased renal blood flow –> decreased GFR by 10%
    eg. Congestive heart failure, dehydration, hypotension
  2. Increased protein breakdown –> increased urea production (no effect on GFR)
    eg. GI bleed, burn, fever, too much protein
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9
Q

Explain Intrarenal causes that elevate BUN (2)

A
  1. Acute renal failure
    - Nephrotoxic drugs
    - severe hypertension
    - Glomerular nephritis
    - Tubular nerosis
  2. Chronic renal failure
    - diabetes
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10
Q

Explain post-renal causes that elevate BUN (2)

A

Obstruction of urine flow (post-kidney
- Ureter
- bladder neck
- Urethra

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11
Q

Reference range for Serum Creatinine SCr? Where does it come from? how is it eliminated? Does diet or urine flow affect it?

A

58-110 mmoles/L
- Marker of renal function
- Comes from breakdown of creatine phosphate
- eliminated through GF

  • not affected by diet or urine flow
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12
Q

Explain renal and non-renal causes of elevated SCr

A

Renal: due to decreased GFR = less creatinine clearance

Non-renal (temp. increase): large meal of meat, vigorous exercise, increased muscle mass

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13
Q

Explain the causes of decreased SCr

A

Decreased muscle mass/activity
eg.
Coma
Taking neuromuscular blocking agents
Patients with spinal cord injuries
Elderly

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14
Q

What is the rule of thumb for SCr normal renal function

A

Stable SCr = normal renal function
- doubling value into reference range is more dangerous than consistency below range

15
Q

What reflects the changes in GFR? how/ what is the trend?

A

SCr increases, there is a delay depending on renal function
- the worse the renal function the longer it’ll take to adjust

16
Q

Reference range for creatinine clearance (CrCl)? what is it used to?

A

90-140 mL/min
Used to
- assess kidney function
- monitor effect of drugs on slowing progression of kidney disease
- monitor patients on nephrotoxic drugs
- determine dose adjustments for renally eliminated drugs

17
Q

What is the relationship between SCr and CrCL and renal function? when does SCr rise?

A

SCr is inversely proportional to CrCL and renal function
CrCL function = renal function

Before SCr rises:
- decline in CrCL
- 50% of nephrons are non-functional
- because of this, SCr alone is not a good indicator of early decreased kidney function

18
Q

What is the requirement for measuring CrCl?

A

Requires 24 hour urine collection
- time consuming, labour intensive

19
Q

What are drawbacks of the Cockcroft-Gault Equation

A
  • Based on small study only on men
  • Based on patients with stable SCr value, so not useful for changing renal function/SCr
  • Misleading for SCr affected by non-renal factors
  • DOES NOT CONSIDER BODY SURFACE AREA
20
Q

What are drawbacks of the Schwartz equation

A
  • May overestimate CrCL
  • only for paediatric patients 1 week- 18 years
  • not for changing SCr/ renal function
21
Q

What are the drawbacks of the Modification of Diet in Renal Disease (MDRD) equation?

A
  • estimates ONLY GFR, NOT CrCL
  • not for changing SCr/renal function
22
Q

What happens if we use the equations for rapidly decreasing/increasing SCr value?

A

SCr decreasing –> underestimate of renal function (good function) = reduce dose unneccesarily

SCr increasing –> overestimate of renal function (bad function) = increase dose too high for kidneys to handle

23
Q

What happens if you use the equations for patients on dialysis

A

Dialysis machine removes Cr –> underestimate of renal function (good function)

24
Q

What consideration for CrCL measurement if renal dysfunction is temporary or chronic?

A

Temporary: IV rehydration
Chronic: use CG/MDRD equation -> SCr levels are stable

25
Q

Consideration for drug response with urgent or non-immediate symptom cases

A

Urgent: start with normal dose and reasses renal function

Non-urgent: start low and tritrate up to response or toxicity

25
Q

What consideration should you take with size of therapeutic window?

A

Careful with drug with narrow therapeutic window. Start low, go slow

25
Q

When should CG equation be used?

A
  • when determining dosing recommendations and dosing adjustments
  • since it is a measure of actual CrCL and not relative renal function
26
Q

When should MDRD equation be used?

A

MORE ACCURATE
- used to estimate GFR

ipfc 1 midterm 1 (8 decks)

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