Non Protein Nitrogen

• Monitor and asses renal function.
• Result from the breakdown of protein and nucleic acids.

UREA

• Most abundant (45-50%) NPN
• Major end product of protein metabolism
• First metabolite to increase in kidney dxs
• BUN:Crea Ratio 10:1-20:1
• Urea is decreased in severe hepatic dxs
• Methods:
  • Micro-Kjeldahl Nesslerization method
    • Indirect method
    • Nitrogen x 2.14 = urea x 0.467 = BUN
  • Rosenthal method
    • Direct method
    • Diacetyl monoxime method
  • Enzymatic method
    • Urease
  • IDMS
    • Reference method

CREATININE

• Major end product of muscle catabolism
• Produced by three AA: methionine, arginine and lysine
• Index of overall renal function
• Evauluate fetal kidney maturity
• 100% is excreted
• Creatine: 100% is reabsorbed by kidney
• RV:
  • Male = 0.9 – 1.3 mg/dL (80 – 115 umol/L)
  • Female = 0.6 – 1.1 mg/dL (53 – 97 umol/L)
• Methods:
  • Jaffe reaction
  • Note: falsely elevated in px taking caphalosporin
    • Color reagent: Alkaline picrate
    • Lloyd’s reagent: sodium aluminum silicate
    • Fuller’s Earth: aluminum magnesium silicate
    • Enzymatic method
      • Creatinine aminohydrolase CK Method
      • Creatinase-hydrogen peroxide method

AMINO ACIDS

• Building blocks of proteins

AMMONIUM

• Used to monitor hepatic coma
• Important indicator of Reye’s syndrome

URIC ACID

• Major product of purine metabolism
• Forms crystals in joints (tophi)
• Methods:
  • Folin method
  • Henry’s method
  • Enzymatic method