Chem Path - Assessing renal function Flashcards
Best method of measuring kidney function?
GFR
Normal is 120ml/min
Age related decline of 1ml/year
What is the clearance formula?
C = (UxV)/P
U=Urinary conc, V=Urinary flow rate, P=plasma conc
If there is no funny business going on (marker binding to serum proteins, being reabsorbed or not being filtered properly), then C = GFR
Inulin = gold standard but requires steady IV drip
How is Urea as a endogenous marker of GFR?
Bad
Firstly, it has variable reabsorption.
Secondly, many factors can affect its level.
- Protein levels in diet (↑ urea)
- Liver function (impaired function can cause low urea)
- GI bleed (↑urea)
How is Creatinine as a marker of GFR?
Pretty good
Freely filtered in kidney - very good.
It can be variable between people
- ↑ in black people
- ↑ with more muscle mass
- ↑ with high protein diet
- Secreted into urine by renal tubules
But it is a good marker of trend. Currently used to calculate eGFR - takes into account age, gender and ethnicity using special formula.
Can a urine sample accurately measure proteinuria?
Yes!
Protein:Creatinine ratio can be used to estimate well
What can a 24h collection be useful for?
Creatinine clearance estimation - may be more accurate than 1 sample
Stone forming elements - see what’s causing stone
Can urine dip exclude haematuria?
Yes
It is very sensitive (sometimes overly sensitive).
Can also be positive with myoglobin - which is nephrotoxic!
Does a negative dip for nitrites exclude bacteria?
No
Gram +ve might not show nitrite signs.
Does a negative dip for leucocytes exclude white cells?
Yes
This is significant
Is a urine sample able to detect bence jones proteins?
No
Bence Jones proteins are found in multiple myeloma
Is a urine test diagnostically useful for diabetes?
Technically yes, but not as good as blood. Still need a blood result to diagnose diabetes.
What would calcium oxalates on urine microscopy suggest?
Kidney stone
Ethylene glycol poisoning is another possibility and this would be more likely if Pt was acting intoxicated. 1st stage of ethylene glycol poisoning would mimic alcohol poisoning.
Will progress to kidney failure or death if untreated
What would RBC casts on microscopy suggest?
Glomerulonephritis
SLE, Goodpastures, Post-strep, Wegener’s
What would epithelial casts on microscopy suggest?
Acute tubular necrosis and toxins (mercury, diethylene glycol, mercury, salicylate)
What is 1st line radiological test for kidney stone?
CT KUB
Plain KUB if no money
