C12 Non-Protein Nitrogens Flashcards
What are NPNs?
Increased in renal failure and are commonly ordered as blood tests to check renal function
Most important NPNs?
BUN, Creatinine, Uric Acid, and Ammonia
BUN
Blood Urea Nitrogen, 50% of NPNs, urea, filtered by glomerulus but also aborbed by renal tubules (40%), some is lost through the skin and GI tract (<10%)
Urea
by product of protein catabolism which produces ammonia
Ammonia
very toxic- converted to urea by the liver
Liver converts ammonia and CO2 into?
urea
Plasma BUN is affected by?
renal function, dietary protein, and protein catabolism
Azotemia
elevated plasma BUN
Prerenal (increased) BUN- not related to renal function
low bp, decreased flow to kidney, increased dietary protein or protein catabolism
increased BUN/normal creatinine
Prerenal (decreased) BUN- not related to renal function
decreased dietary protein, increased protein synthesis (pg women and children)
Renal causes of (increased) BUN
renal disease with decreased glomerular filtration (glomerular nephritis, renal failure from DM)
Post renal cause of (increased) BUN-not related to renal function
obstruction of urine flow- kidney stones, tumors, UTIs
increased BUN/increased creatinine
Renal decreased BUN
low dietary protein or severe liver disease
decreased BUN/normal creatinine
Creatinine
formed at a constant rate by the muscles as a function of muscle mass, removed from plasma by glomerular filtration, not secreted/absorbed by the renal tubules
Liver
Amino acids>creatinine
Muscles
Creatinine>phosphoscreatinine
phosphocreatinine>creatinine
Plasma creatinine?
function of glomerular filtration, unaffected by other factors, its a very good test to evaluate renal function
delta check
significant change from previous results
Jaffee Method
creatinine analytical technique
Creatinine+Picrate Acid>colored chromogen
Specimen-plasma/serum
elevated bilirubin and hemolysis causes falsely decreased results (everyone uses this technique)
Uric Acid
breakdown product of purines (nucleic acid/DNA), converted from liver, filtered by glomerulus (98-100% reabsorbed)
Elevated plasma uric acid?
can promote formation of solid uric acid crystals in joints and urine
Uric acid diseases?
Gout (increased plasma uric acid, acid crystals in joints, associated with alcohol consumption, may also form kidney stones)
Leukemias and lymphomas
Megaloblastic anemias
renal disease
Uric acid absorbs light at?
293 nm, rate of decreased absorption is proportional to the uric acid concentration
Ammonia
produced from the deamaination of amino acids, bacterial enzymatic conversion of GI tract protein, muscle catabolism
Causes of increased ammonia
liver disease, Reye’s syndrome, sever renal disease, genetic enzyme dificiencies of the urea cycle, Valproic acid (anti-seizure medications)
Ammonia analytical technique
decreasing absorbance @340 nm proportional to the ammonia concentration
EDTA/Heparinized whole blood on ice, delayed testing causes false increase values
Creatinine clearance
calculated measurement of the rate at which creatinine is removed from the plasma by the kidneys, measurement of glomerular filtration
Creatinine is?
an endogenous substance (not affected by diet), filtered by glomerulus but not secreted or reaborbed by renal tubules
Creatinine clearance specimens?
24 hr urine specimen
plasma/serum creatinine collected during the urine collection
Creatinine Clearance Formula
(UV//P)(1.73/A)
U=creatinine concentration of the 24 hr urine (mg/dl)
V=24 hr urine volumes, V=V/1440=ml/min
P=plasma creatinine concentration (mg/dl)
A=correction factor accounts for differences in BMI
