lab Diagnosis lecture - renal tests Flashcards
what does renal function testing tell us?
renal blood flow, GFR, and tubular function
what does renal disease imply
presence of histological leasions in kidney, not degreee of dysfunction
renal failure
75% of total nephron pop is non functional, not necessarily histological lesiona, could be dehydration
what are the two main categories of renal testing
- to evaluate clearance, 2. evaluate tubular function
What 4 tests are to evaluate clearance?
Blood urea nitrogen(BUN), Serum Creatinine, Creatinine clearance , Albumin creatine ratio
what are the tests to evaluate tubular function?
fractional excretion of NA+
What is GFR
measure of volume of plasma from which a substance is removed by glomerulus
what is the most frequently preformed renal function test
GFR
what is importaint in substance to measure GFR
1.filtered through Glom, 2.non protein bound, 3.not used in body, 4.only way out is kidneys, 5.doesn’t do anything at renal tubules, 6. stable in blood and urin, 7. easily measured
What does blood nitorgen come from
protein catabolism
What makes the BUN not accurate without calculations in urine?
100% is filtered by the glomerulus, then 40% is reabsorbed by tubules, so your clearance is only 60% of actual
What is serum plasma testing for?
evaluate liver function, rough indicator of GFR and renal blood flow althoug its indirect
serum plasma testing is part of what pannel
CMP comprehensive metabolic pannel or basic metabolic pannel, BMP
what can decreas BUN levels
pregnancy and liver disease, malnutrion, overhydration
asotemia
increased blood urea nitrogen
Prerenal causes of Bun increase, azotemia
Low blood volume, CHF, MI, GI bleed, High protein, Starvation, Sepsis
Renal causes of azotemia, BUN increase
Renal disease, glomerulonephritis, pyelonephritis, tubular necrosis, drugs
Post renal causes of azotemia, Bun increase
Ureter obstruction, bladder outlet obstruction (prostate)
What is a more stable marker than BUN?
Serum creatinine, a catabolic product of creatine phosphate from skeletal muscles.
Does BUN or Creatinine increase first?
BUN increases first, then serum creatinine
why would old and young have decreased creatinine
reduced muscle mass.
How much creatinine is filtered by kidneys
almost completely filtered by glom and secreated at proximal tubule
what is serum creatinine used to diagnose?
imparied renal function because its not as affected by liver function as BUN
what is importaint to remember about how renal disease effects BUN and creatinin
large changes in GFR early in disease don’t change it much, only at the late stages of renal disease do changes big enough for thiese tests to pick up happen. So it only picks up later stage renal disease.
when taking the bun/creatine ratio, how would you know if the problem base prerenal increase(azotemia)
If the amount of BUN is 20 or more times that of Creatinine
if the RUN /creatinine ratio is 10-20 :1, what does that indicate?
Renal Azotemia- chronic kidney disease, glomerular damage, tubular necrosis
With what azotemia would you be able to pick up on dip stick?
Protein in urine during Renal axotemia
what happens as GFR goes down?
serum creatine goes up
eGFR
estimated GFR calculated using serum creatine
what would make eGRF inacurate
Vegetarian, malmurished, old or young,
when you need a more accurate estimate of GFR use what?
creatinine clearance
How doe you get creatinine clearance
24 hour urine collection and blood draw that are analyzed for creatine then calculated by using patients height and weight
does creatine clearace over or underestimate GFR?
Overestimates GFR by 10% due to tubular secreation.
at what point will the GFR from CC, creatinine clearance be invalid?
when the GFR is less than 30% of normal
what happens to CC as you age
decrease 6.5 ml/min each decade after 20.
what can increase CC?
exercise, pregnancy and drugs, low if incompelte urine
What test is superior to serum creatine?
cystatin C, estimates GFR independent of age, musclemass and liver damage
how will tests tell me its acute renal failure
occurs over hours/days, no broad casts in urine sedament, absent anemia, kidney size, renal function hx seen normal
how will tests tell me its chronic renal failure?
gradual over time, increased BUN and creatinine, small kidney, anemia present, broad casts in urine
what is the most common cause of acute renal failure
pre renal and tubular necrosis
how would you determine the difference between pre, and renal acute renal failure?
Fractional socium excretion
if its Pre renal, sodium does what
FEN is 1%
if its renal Acute failure FEN is what?
FEN is greater than 2%
