Biochemical Measurements Flashcards
what are the two methods of testing glomerular function
glomerular filtration rate and proteinuria
what happens in the proximal tubule
sire of main reabsorption
what happens in the distal tubule
secretion
what happens in the loop of henle
concentration of filtrate
the perfect marker of GFR is inulin- why is it not used clinically
impracticable, not endogenous have to inject it
what is the urea cycle
the end of protein metabolism
how is urea transported
from gut to liver in portal system
leaves liver and goes into systemic circulation where most excrete but 25% goes back into go (extra renal elimination, limits its value for measuring GFR)
what is urea
end product of protein metabolism in the liver
why is urea not as good at measuring GFR
extra renal elimination dietary dependent (doesnt appear at a constant rate) is reabsorbed in the renal tubule (e.g urea in blood will increase if you loose lot of blood/ water as filtration rate goes down)
what produces creatine
muscle
what happens to creatinine in the body
renal excretion (90-95% filtered, 5-10% secreted by distal tubule)
is creatinine secreted into the renal tubule
yes (only downfall of it to measure GFR- but only 5-10%)
how do you assess GFR
eGFR (can also use creatinine or serum creatinine clearance)
what happens to serum creatinine as GFR decreases
it rises (not being filtered from blood)
what it then normal GFR value
above 120 mL/min
below what GFR does serum creatinine leave the reference interval
not until below 60 (not sensitive to changes in GFR until quite low)
what measure of creatinine is more sensitive to changes in GFR at values above 60
urine creatinine clearance
what affects serum creatinine
age (young higher) sex (males generally higher) muscle mass (more muscle higher) diet (poor= lower) ethnicity (higher if black)
what is eGFR (4 variable MDRD)
estimated GFR- adjusts serum creatinine for the confounding factors (age, sex, muscle mass)
what is serum creatinine clearance
represents volume of plasma that is theoretically cleared of a substance per minute
(urine creatine conc x urine volume) / (serum creatine conc x duration of collection)
(can have high creatinine but be healthy as you making and excreting lots)
what are the CKD stages
1= kidney damage with normal/ ^ GFR (GFR>/= 90)
2= kidney damage with mildly decreased GFR (60-89)
3= moderatly decreased GFR (30-59)
4=severely decreased GFR (15-29)
5 kidney failure (<15/ dialysis)
what is proteinuria a sign of
reduce glomerular function (plasma proteins shouldn’t be in urine)
how can you estimate proteinuria
24 hour urine collection
protein/creatinine ratio
proteinuria over what is suggestive is significant of glomerular damage
> 150 mg/day
what type of proteinuria is multiple myeloma
overflow (cancer of plasma cells (b lymphocyte that produces immunoglobulins) causes overproduction of the Ig= too much protein, kidney unable to filter it all)
what type of proteinuria is albuminuria
glomerular (glomeruli not working as effective filter, abnormal proteins in urine. loose proteins (albumin) in urine which reduces oncotic pressure in capillaries so fluid moves into the interstitial fluid)
what creates oncotic pressure
albumin
what is anasarca
gross oedema
what is microalbuminuria
excretion of albumin in abnormal quantities, below the limit to be detected by a dipstick
what are the normal albumin creatine ratio figures
<2.5 males
<3.4 females
what is the earliest expression of diabetic nephropathy
microalbuminuria
what cant help stop progression of diabetic nephropahty
ace inhibitor
what is tubular function
the reabsorbtion of important substances (water, electrolytes, amino acids, glucose) from the filtrate
what are the pre renal causes of oliguria
reduced renal perfusion (blood loss)
what are the post renal causes of oliguria
ureteric/uretheral obstruction (stones/malignancy)
what are the renal causes of oliguria
intrinsic kidney tissue damage (glomerulonephritis, nephrotoxins)
what is uremia
high levels of urea in the blood
what happens to the components of urine when renal tubules stop working
increased urine sodium
decreased urine/serum urea (urine should always be much higher than serum)
urine/serum osmolality almost 1:1
how does urine:serum osmolality show tubular function
urine osmolality should be much higher than serum
if ratio is close to one the tubules not filtering effectively as both liquids similar osmolality
what is the commonest cause of proteinuria
glomerular (e.g. albuminuria, microalbuminuria)
what is the best method for measuring tubular function
urine:serum osmolality
