CLINICAL CHEMISTRY CHAPTER 9. NON - PROTEIN NITROGEN. Introduction. NPN ( Non - Protein Nitrogen ) is a “funky” term that can be used for a bunch of different substances that have the element nitrogen in them, but are not proteins.
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NON - PROTEIN NITROGEN
BUN / Creat Ratio
Hyper ( hypo ) uricemia
Reyes SyndromeKey Terms
2 NH4+ + HCO3-
NH4+ + 2-OXOGLUTARATE
Measure the rate of decreased absorbance at 340 nm
NADH absorbs … NAD does not absorb
Reference range : 10 – 20 mg / dl
Liver Amino Acids Creatine
Muscles Creatine Phosphocreatine
Muscles Phosphocreatine Creatinine
Creatinine formed at a constant rate by the muscles as a function of muscle mass
Creatinine is removed from the plasma by glomerular filtration
Creatinine is not secreted or absorbed by the renal tubules
Therefore : Plasma creatinine is a function of glomerular filtration
Unaffected by other factors
It’s a very good test to evaluate renal function
Creatinine + Picrate Acid Colored chromogen
Specimen : Plasma or serum
Elevated bilirubin and hemolysis causes falsely decreased results
Reference range : 0.5 - 1.5 mg / dl
URIC ACID Creatine
Breakdown product of purines ( nucleic acid / DNA )
Purines from cellular breakdown are converted to uric acid by the liver
Uric acid is filtered by the glomerulus ( but 98 – 100 % reabsorbed )
Elevated plasma uric acid can promote formation of solid uric acid crystals in joints and urine
Uric acid + O2 + H2O
Allantoin + CO2
Uric acid absorbs light @ 293 nm , Allantoin does not.
The rate of decreased absorption is proportional to the uric acid concentration.
Specimen : Plasma or serum
Reference range : 3.5 - 7.2 mg/dl (males)
2.6 - 6.0 mg/dl (females)
Let’s remember 3.0 - 7.0 mg/dl
Ammonia analytical techniques Creatine
NH4+ + 2-OXOGLUTARATE + NADPH L-GLUTAMATE +
There is a decreasing absorbance @ 340 nm, proportional to the ammonia concentration.
Specimen : EDTA or Heparinized Whole Blood on ice
Must be tested ASAP or plasma frozen
Delayed testing caused false increased values
Reference range : 20 – 60 µg / dl
24 Hour Urine collection Creatine
The volume can be measured
directly off the container.
U = Creatinine concentration of the 24 hour urine ( mg / dl )
V = 24 hour urine volume ( mls ) per minute - V / 1440 = mls / minute
P = Plasma creatinine concentration ( mg / dl )
A = Correction factor accounts for differences in body surface area
obtained from a height – weight chart
24 hour urine volume = 1000 mls
24 hour urine creatinine = 20.0 mg / dl
Plasma creatinine = 5.0 mg / dl
Patients height / weight = 6’00 / 190 lbs ( see pg. 680 )
Creat Cl = 2 ml / min …. Very poor clearance !!!
Don’t forget to divide V by 1440 !