Lecture 4-Measurement of Kidney Function Flashcards
What is GFR?
Glomerular filtration rate = amount of filtrate produced from blood flow per unit time
What is the normal range for GFR?
90-120 ml/min/1.73m^2
What does GFR depend on?
Gender, age, size of individual and kidneys, pregnancy
When does nephron development finish?
35th-36th week of development
After what age does GFR start to decline?
30 y/o
What can compensatory hypertrophy of nephrons lead to?
Cortical scars and atrophy due to poor blood supply
What is clearance?
Volume of plasma cleared of substance per unit time
What is the equation for clearance?
C = A (amount of substance eliminated from plasma) / P (plasma conc of substrate)
What is renal clearance?
[U (amount of urine) x V (urine flow rate)] / P
If used to measure kidney clearance, a substance should have what properties?
- be produced at a constant rate
- be freely filtered
- not be reabsorbed
- not be secreted
What is the best GFR marker?
Inulin
Why is inulin not used to measure GFR?
It requires constant IV and needs a catheter and timed urine collections
Which radioactively labelled marker can be used to measure GFR?
51 Cr-EDTA
True or false: 51 Cr-EDTA has a 20% lower clearance than inulin
FALSE - 10%
Which is the most commonly used marker for GFR?
Creatinine
What is creatinine?
End product of muscle breakdown
Is creatinine clearance an overestimate or underestimate of GFR?
Overestimate by 10-20% because it is secreted into the nephron
What affects creatinine levels?
- intake
- metabolism
- bowel excretion
- renal excretion and secretion
What can increase serum creatinine?
- large muscle bulk
- black male
- supplements, lots of meat
- drugs (trimethoprim)
What can decrease serum creatinine?
- reduced muscle mass
- old, hispanic/Indo-Asian female
- vegetarian
Why is serum creatinine high in early childhood?
High when still in mother because levels will be same as mother’s and will then decrease
What is eGFR based on?
- serum creatinine
- age
- sex
- Caucasian or black
When is eGFR inaccurate?
- people with kidney disease
- children
- pregnancy
- old age
- other ethnicities
- amputees
True or false: eGFR overestimates true GFR
FALSE - underestimates
