Renal Lab Eval Flashcards Preview

Nephrology > Renal Lab Eval > Flashcards

Flashcards in Renal Lab Eval Deck (102)
Loading flashcards...

Kidney's fxn?

- excretion of waste products of metabolism
- regulate excretion of water and solutes (Na, K, and H), through changes in tubular reabsorption or secretion
- secretes hormones: renin, prostaglandins, and bradykinin
erythropoietin, Ca2+, phosphorus, (and calcitriol)


Sxs of kidnney disease?

- gross hematuria, flank pain
- edema, HTN, signs of uremia
- many pts are asx, only sign is elevated serum creatinine or abnorm uirnalysis



- elevated BUN and/or creatinine, buildup of abnormally large amounts of nitrogenous waste products in the blood



- urine output of less than 400 ml a day, or less tahn 20 cc/hr



- hardly any output at all
- less than 100 mL/day


Causes of pre-renal failure?

- volume contraction (dehydration)


Causes of intrinsic renal failure?

- arteriolar damage (acute HTN)
- glomerulonephritis
- ATN (acute tubular necrosis)


Causes of post-renal obstruction?

- ureteral obstruction
- bladder outlet obstruction


What does the GFR tell us? normals? influenced by?

- sum filtration rate of all fxning nephrons
- men norm: 130 mL/min
- women: 120 mL/min
- influenced by: age, sex, body size, RBF and HP in glomerulus


How can the GFR be measured?

- CrCl
- urea clearance
- inulin clearance - 100% filtered, gold std for GFR


What is CrCl? Normals?

- endogenous substance used to assess GFR
- men (Up to 40): 107-139 ml/min
- women: 87-107
- overestimates true GFR by up to 40% because of active tubular secretion of creatinine


How does GFR correlate with kidney disease?

- level of GFR has prognostic indications but isn't the exact correlate to loss of nephron mass
- stable GFR: doesn't imply stable disease
- some pts with renal disease may go unrecognized b/c of normal GFR


What is BUN (blood urea nitrogen)

- urea nitrogen is what is formed when protein breaks down
- normal range: 6-20 mg/dL
- many drugs can effect the BUN
- usually measured with creatinine to monitor kidney fxn


What causes an increase in BUN?

increases when protein is broken down and more ammonia forms:
- renal disease
- excessive protein breakdown (catabolism - tissue necrosis)
- very high protein diet
- GI bleeding***
- burns
- tetracycline
- fever
- decreased GFR: less BUN presented at glomerulus to be removed from the blood
slower transport time through PCT allows more reabsorption


What causes a decrease in BUN?

- liver disease (liver unavailable to convert ammonia to urea then the BUN will decrease and the ammonia increases)
- starvation


Where does BUN come from?

- protein is cleaved from the AA and a nitrogen is left behind so it takes up 3 H+ to form ammonia
- NH3+ is then processed through the liver to become urea
- when urea enters to blood stream it is called BUN
- then it is excreted by the kidney


How does decreased GFR lead to increased BUN?

- 2 ways
1. decreased flow through glomerulus
2. slower transport time allows more BUN to be resorbed at level of PCT


What is creatinine?

- formed from normal breakdown of muscle
- more muscle mass the higher creatinine
- lower the muscle mass the lower the creatinine (normal reduction in creatinine as a person ages and loses muscle mass)


Normal range of creatinine?

- waste product of protein breakdown excreted by the kidneys
- normal range: men - 0.8-1.4
women: 0.6-1.2
- 50% loss of renal fxn is needed to increase serum creatinine from 1-2 mg/dL
- used in ratio with BUN to determine types of azotemia


In what situations is creatinine increased?

- renal failure
- diet: increased digestion of meats
-meds: ACEIs, diuretics, NSAIDs
- muscle disease/breakdown: muscular dystrophy, rhabdomyolysis
- blockage at sites in DCT that allow for active secretion
- decreased GFR as there is less creatinine presented at glomerulus to be filtered out


when would creatinine be decreased?

- pregnancy: normal occurence
- range in pregnancy: 0.4-0.6 mg/dL (increased volume)


What happens to creatinine with a decreased GFR?

- increases
- instead of creatinine being reabsorbed in the tubules like BUN with a decreased GFR the creatinine is just dumped out
- in the DCT creatinine is actively secreted from the body to be eliminated by the kidneys
- this active secretion at the DCT can be blocked by drugs such as cimetidine and trimethoprim therefore increasing serum creatinine


Normal range of BUN/creatinine ratio?

- normal: 10-20.1
- elevated: greater than 20.1
- increased ratio in a low flow (low BP) state
- BUN/serum creatinine


When is BUN/creatinine ratio increased with normal creatinine?

- prerenal disease (decreased renal perfusion)
- catabolic state with increased tissue breakdown
- GI hemmorrhage
- high protein intake
- certain drugs: tetracycline, steroids


When is BUN/creatinine ratio increased with elevated creatinine?

- postrenal disease (obstructive uropathy)
- prerenal disease superimposed on renal disease


When is decreased BUN/creatinine (less than 10:1) with decreased BUN occur?

- acute tubular necrosis (intrarenal disease)
- low protein diet, starvation, severe liver disease
- repeated dialysis
- pregnancy


When is BUN/Creatinine decreased with increased creatinine?

- rhabdomyolysis
-muscular pts who develop renal failure


Normal values for Na and K?

- Na+: 135-145 mmol/L
- K+: 3.8-5.5 mmol/L


Normal values for anions?

- chloride: 98-106 mmol/L
- bicarb: 21-28 mmol/L
- total CO2: 23-30 mmol/L


substances that are normally reabsorbed in the kidneys?

- Na+
- K+
- urate
- chloride
- Ca2+
- phosphate ions
- glucose
- AAs