Biochemistry Flashcards
What are the positive points for inulin as a measure of GFR?
Constant rate Freely filtered at glomerulus Not reabsorbed Not secreted No extra-renal eliminiation
Why is inulin not used?
It would need to be inputted as oral/injectible form and wait for it to be metabolised.
Hard to measure
What is urea?
End of product of protein metabolism
Where does the urea cycle occur?
in liver
Why is urea not suitable for eGFR ?
One quarter of elimination does not occur in kidneys
What will increase urea output?
Heavy protein intake
What is creatinine?
Product of muscle breakdown
Why is creatinine not a perfect marker for GFR?
Small amount is secreted by distal tubule
What is the normal for GFR?
120
What is the maximum number given for eGFR?
60.
Harder to measure in bigger numbers
What is the issue with using creatinine as a marker of GFR?
Not sensitive to changes in GFR until it is significantly reduced
What is clearance?
The volume of plasma that is cleared of a specific substance per minute
How is urinary creatinine clearance worked out?
[creatinine]urine X urine volume / [creatinine]serum x duration of collection
What factors impact on serum creatinine?
Muscle mass Age Sex Diet Ethnicity
If a very accurate eGFR is necessary then what is used?
Chromium- EDTA
What is the gold standard for measuring proteinuria?
24 hour collection
Obviously not practical
What test can be done relatively simply for proteinuria?
Protein:creatinine ratio
How much protein must be excreted/day to be significant?
Over 150mg
What is overflow proteinuria?
Proteinload is too much and kidney cannot reabsorb all of it.
When is overflow proteinuria common?
Multiple myeloma
What is glomerular proteinuria?
A normal amount of protein but the glomeruli do not filter it and cannot all be reabsorbed
What is tubular proteinuria?
Microglobulins usually go through the glomeruli but in tubular they are not reabsorbed
What is a key histological sign of multiple myeloma?
Eccentric nucleus.
Nucleus not in centre
What is multiple myeloma?
Malignancy is uncontrolled multiplication of B lymphocytes to make immunoglobulins
What is sometimes described on x-ray with multiple myeloma?
Pepper pot appearance in skull
What is microalbuminuria?
Excretion of albumin, below limits of protein detention by dipstick
What can microalbuinuria be a sign of?
Diabetic nephropathy
If hypertensive and microalbuminuria then what drug is given?
ACEI
What 3 classes of pathology can cause oliguria?
Pre-renal
Renal
Post renal
Give an example of a pre-renal issue
Reduced renal perfusion e.g. hypovolaemia
Give an example of a renal cause of oliguria
Intrinsic kidney damage e.g. glomerulonephritis
Give an example of a renal cause of oliguria
Ureteric obstruction e.g. stones or malignancy
What biochemical measurements are necessary to figure out the cause of oliguria?
Urine osmolality
Serum osmolality
