Investigation of Non-Protein Nitrogen Compounds

Investigation of Non-Protein Nitrogen Compounds

  • Focus on compounds in the body that contain nitrogen but are not part of proteins.

Key Non-Protein Nitrogen Compounds

  • Ammonia: Produced from the catabolism of amino acids.
  • Urea: Major end product of nitrogen metabolism; formed in the liver and excreted by kidneys.
  • Creatinine: Waste product from muscle metabolism.
  • Uric Acid: Product of purine metabolism; forms crystals in joints (gout).
  • Bilirubin: Breakdown product of hemoglobin.

Ammonia Metabolism

Origin
  • Catabolism of amino acids (deamination).
  • Hydrolysis of glutamine to glutamate.
  • Catabolism of purines and pyrimidines.
  • Suggested contribution from intestinal bacteria.
Elimination
  • Kidneys: Minor role in ammonia elimination.
  • Liver: Predominantly eliminates ammonia by converting it to urea. Hepatic ureogenesis accounts for 95% elimination.
    • Urea is non-toxic and easily excreted; ammonia is toxic and can lead to neurological disturbances (e.g., hepatic coma).
Functionality
  • Ammoniogenesis helps maintain acid-base balance by removing H+ ions during acidosis and conserving Na+ and K+.

Urea Metabolism

  • Process: Urea is synthesized in the liver (ureogenesis) and excreted via kidneys in two phases: glomerular filtration and passive tubular reabsorption.
  • Importance of Urea Measurement: Commonly done to evaluate kidney function alongside creatinine measurements.

Sample Collection for Testing

  • Blood Samples: Fasting, collected in anticoagulant tubes (EDTA or lithium heparinate). Transport on ice to minimize ammonia production from deamination.
  • Urine Samples: 24-hour collections, using antiseptic solutions to prevent contamination.

Dosage Methods for Analyzing Ammonia

  • Micro-titration Methods
  • Colorimetric Methods: Nessler's Reaction and Berthelot Reaction.
  • Other Techniques: Electrochemical and enzymatic methods.

Additional Diagnostic Tests

  • Measuring activity of urea cycle enzymes (e.g., CPS, OCT).
  • Blood amino acid and urinary organic acid chromatography.
  • Assessment of orotic acid and carnitine levels.

Normal Values for Ammonia & Urea

  • Ammonia (Blood): 14 to 38 μmol/L.
  • Urea (Urine, 24h): 30 to 60 mmol.

Pathological Variations

Acquired Conditions:
  • Metabolic acidosis (also increases NH4+).
  • Liver insufficiency (e.g., cirrhosis).
  • Effects of certain medications (e.g., Depakine).
Inherited Disorders:
  • Urea cycle deficiencies (e.g., lack of CPS or OCT).
  • Organic acidurias and metabolic disorders affecting nitrogen elimination.

Creatinine Metabolism

Overview
  • Origin: Creatinine is a waste product from creatine breakdown in muscles.
  • Functionality: Excreted via kidneys; relevant for kidneys assessment.
Sample Collection for Creatinine
  • Adequate collection techniques preserve sample integrity (avoid hemolysis).
Measurement Methods
  • Chemical Techniques: Jaffé reaction for creatinine measurement.
    • Can be affected by interferences from glucose and proteins.
  • Enzymatic Techniques: More specific with less interference.
  • Reference Techniques: HPLC and IDMS for accuracy and standardization.
Normal Creatinine Values
  • Blood:
    • Men: 6 – 12 mg/L
    • Women: 5 – 10 mg/L
    • Children: 4 – 9 mg/L
  • Urinary Excretion: Average 1 to 2 g/day.

Pathological Conditions Related to Creatinine Levels

  • Hypercreatininemia: Indicative of acute or chronic renal failure.
  • Hypocreatininemia: May indicate muscle atrophy or severe myopathies.

Uric Acid and Its Metabolism

Overview
  • Uric acid arises from purine metabolism; primarily eliminated via the kidneys.
  • Forms sodium urate, which can precipitate in joints, causing gout.
Diagnosis of Gout
  • Symptoms include sudden pain, swelling in great toe, and elevated serum uric acid levels (>9 mg/dL).
Sample Types for Uric Acid Analysis
  • Blood (dry tube or heparinized) and urine (24-hour collection).
Normal Uric Acid Ranges
  • Blood Uric Acid:
    • Men: 30 to 70 mg/L
    • Women: 25 to 60 mg/L
  • Dietary Effects: Diet rich in purines can raise uric acid levels.

Bilirubin Measurement and Clinical Relevance

Overview
  • Total bilirubin levels can indicate liver function and disease.
Sample Collection for Bilirubin
  • Must collect under specific conditions to avoid hemolysis and light exposure.
Dosage Methods of Bilirubin
  • Alkalinization techniques and colorimetric assays for measuring bilirubin levels.
Normal Bilirubin Values
  • Adults: Total bilirubin 6 to 10 mg/L, Conjugated < 2 mg/L.
Pathological Variations
  • An increase in bilirubin indicates jaundice, with specific conditions leading to either unconjugated or conjugated bilirubin elevation, requiring careful differential diagnosis.