CC LAB: RENAL FUNCTION

• All proteins have nitrogen group, not everything that has nitrogen is a protein
• Nephrons


  Function unit of kidney
• Glomerulus


  • Filtration
  • Large particles does not pass through
  • Non protein may enter
  • Amino Acid can pass through
• Kidney function


  1. Secretion

  2. Reabsorption
• Excretion: analytes secreted to urine
• Amino acid


  Not Protein, Has Nitrogen
• Afferent


  Blood enters
• Efferent


  Blood exits
• Non Protein


  • Urea
  • Amino Acids
• Blood Urea Nitrogen (BUN)


  Most abundant
• Protein breakdown


  Protein> Amino Acid> Ammonia> Urea
• Protein absorption and synthesis


  1. Absorb proteins from diet> Travel to liver (Protein Synthesis)

  2. Protein must be breakdown/converted to amino acid then converted to Protein by the Liver for the use of protein synthesis
• Deamination


  Amino Acid remove Amine group> NH2
• Ammonia is toxic for the CNS (Hyperammonemia)
• Urea


  • Main waste product of Nitrogen-containing chemical in the body
  • Approximately 90% of the Nitrogen excreted
  • Major end product of protein (dietary) and amino acid catabolism
• Liver damage


  • Amino acid decrease (Deamination of proteins)
  • Small portion of hepatocytes can convert ammonia to urea
  • Toxic accumulation of Ammonia
• All waste product must be eliminated by the kidney
• Urea


  • Widely used as a measure of renal dysfunction but its value as a measure of GFR is not plausible
  • Freely filtered by the glomerulus but is reabsorbed (approx 40%) in some parts of the nephron
• Urea rises if there is 50% dysfunctional kidney
• Glomerular filtration


  PCT Descending Loop of Henle> Ascending Loop of Henle> Distal Convoluted Tubule> Convoluted Tubule> Urine
• 40-60% of urea is reabsorbed
• If urea secretion is detected, it means blood vessel has urea that is transported to tubules
• Criteria for 100% filtered urea: 1) 100% filtered, 2) 0% reabsorbed/secreted, 3) 100% detected by the urine
• Blood Urea Nitrogen (BUN)


  • To evaluate renal function
  • To assess hydration status
  • To determine nitrogen balance
  • To aid in the diagnosis of renal diseases
  • To verify adequacy of dialysis
• Fluoride or citrate inhibit urease which converts urea to ammonia
• Urine should be refrigerated if it cannot be analyzed within an hour
• Alcohol intake can falsely decrease BUN
• Urea Nitrogen


  • Urea Nitrogen (mg/dL) x 2.14 = Urea (mg/dL)
  • Urea Nitrogen (mg/dL) x 0.36 = Urea (mmol/L)
• Conventional method for urea measurement


  1. Hydrolysis of urea by urease

  2. Quantification of NH4+ (Ammonium Ion)

  3. Nessler's reaction

  4. Berthelot's reaction with Nitroprusside
• Nesslerization

  Potassium Mercuric Iodide> Brown Compound
• Berthelot


  Phenol> Indophenole> Blue Compound
• Kinetic method for urea measurement


  1. 2 enzymes used: Urease and GLDPH

  2. Measures the disappearance of NADH @340nm
• Glutamate Dehydrogenase (GLDPH)


  NADH> GLDH > NAD+ (Decrease)
• Diacetyl monoxime (direct method) for urea measurement


  Urea reacts directly with diacetyl monoxime in strong acidic condition to form a yellow diazine derivative @540nm
• Alpha-phthalaldehyde method can immediately detect urea
• Isotope Dilution-Mass Spectrometry (ID-MS)


  Gold standard reference method for non-protein, nitrogen
• Creatine is oxidized to form creatinine
• Creatine


  • Synthesized primarily in the liver from arginine, glycine, and methionine
  • Transported to tissues and converted to creatine phosphate (phosphocreatine), which serves as a high-energy source
  • Needed for muscular movement
• Creatinine


  • Endogenous substance with a molecular weight of 113 daltons
  • Waste product of muscle metabolism
  • Released into the circulation at a relative constant rate in proportion to an individual's muscle mass
• Creatinine

  • Most widely used marker for GFR
  • Endogenous substance with constant rate of production
  • Not bound to plasma proteins
  • Not reabsorbed by the tubules
  • Only a small amount is secreted by the tubules