Biochemistry Flashcards
What criteria should a substance meet to be able to measure Glomerular Filtration rate (GFR)?
- Appear at a constant rate
- Be freely filtered at the glomerulus
- Not be reabsorbed from the renal tubule
- Not be secreted by the renal tubule
- Not undergo extra-renal elimination
Why is Inulin not used to measure GFR if it fits all of the previous criteria?
It is not endogenous (produced by the body)
=> need to give it to the patient and then measure excretion
It is also NOT easy to measure in clinical practice
Why is Urea not suitable for measuring GFR?
It doesnt appear at a constant rate
It is reabsorbed from the renal tubule
It undergoes extra-renal elimination
Where is urea produced?
Liver => end product of protein breakdown
Patients with a large muscle mass produce more Creatinine than those with a normal muscle mass. TURE/FALSE?
TRUE
Why is creatinine not measured for GFR?
It is secreted into the renal tubule
What is considered a normal GFR?
> 120mL/min
If the GFR is very low, what happens to the serum creatinine?
It gets very high
Give an example of creatinine measurement in a pre-dialysis patient?
600-700 micromol/L
Why is creatinine not used as an indicator of GFR?
It is not sensitive to the small changes in GFR
What 4 factors are used to give an estimated GFR (eGFR)?
Age
Sex
Ethnicity
Creatinine
What is meant by urinary creatinine clearance?
volume of plasma that is cleared of creatinine per minute
How do we calculate urinary creatinine clearance?
[creatinine]urine x urine volume
DIVIDED BY
[creatinine]serum x duration of collection
What is urinary creatinine clearance used for?
It is sensitive to GFRs between 100-120mL/min
When would 51Cr-EDTA clearance be used?
Before nephrotoxic agents are given in cancer patients
CKD stage 5 indicates what?
End stage renal failure
When is eGFR not completely accurate?
If it is >60
How do we measure proteinuria?
24 hour urine collection
OR protein:creatinine ratio on a spot urine sample
Protein over what level indicates significant glomerular damage?
> 150mg/day
In Microalbuminuria, no protein is picked up on urine dipstick. TRUE/FALSE?
TRUE
Dipstick test is negative
What does microalbuminuria indicate in certain patients?
earliest expression of diabetic nephropathy
What treatment is given to slow the progression of diabetic nephropathy?
ACE inhibitor
Overflow proteinuria occurs in what condition?
Multiple myeloma
B lymphocyte cancer
Causes plasma cells to make too many antibodies
=> too much protein for glomeruli to handle
Why does nephrotic syndrome occur?
Less protein remains in the blood
=> oncotic pressure pushes fluid from blood to interstitial space
=> oedema occurs
What is normally the cause of a pre-renal uraemia?
Blood loss
What can cause a post-renal uraemia?
Stones/malignancy
What causes are there for a renal uraemia?
Glomerulonephritis or Nephrotoxin
If the urine and serum osmolality are close, this is a good sign. TRUE/FALSE?
FALSE
this means the glomeruli are having no effect on the fluid they are receiving from the blood serum
