Non-protein Nitrogen Compounds Flashcards
Describe non-protein nitrogen compounds
General term that can be used for different substances that have the element nitrogen in them, but are not proteins
Non-protein nitrogen compounds are products of what?
Products from the catabolism of proteins and nucleic acids which includes about 15 different substances (/compounds: NPN fraction)
Non-protein nitrogen compounds are used in evaluating
Renal function and excretion (plasma npns increased in renal failure; ordered as blood tests)
What are the most important NPNs
- BUN (Blood Urea Nitrogen)
- Creatinine
- Uric acid
- Ammonia
Major components of NPN with plasma concenctration (%plasma npn)
- Urea: associated with urine and fertilizer (BUN: 45%)
- Uric acid: increases with intake of protein (20%)
- Creatinine (5%)
- Creatine: component of whey protein (1-5%)
- Amino acids (20%)
- Ammonia (0.2%)
What replaced the measurement of NPN?
determination of blood urea nitrogen (BUN)
It is the nitrogenous end-product of protein or amino acid and nucleic acid metabolism which constitutes 45-50% of NPN
Urea
How is urea synthesized in the liver?
Synthesized in the liver when NH3 is removed and combined with CO2 (Ammonia is very toxic so it is converted to urea)
Other characteristics of urea
- Excreted by glomerular filtration and partially reabsorbed through renal tubules
- Rises quickly as compared to creatinine
- Majority excreted in urine
- Most widely used screening test of kidney function
Normal value of urea
• Normal value: 10–50 mg/dL
Highest concentration of NPN in blood and a major excretory product of protein metabolism (processes which release nitrogen, which is converted to ammonia and synthesized again in the liver from CO2 and ammonia that arises from deamination of amino acids)
Blood urea nitrogen
BUN=urea determination
BUN is excreted by what organ?
Kidneys
• Filtered by the glomerulus but 40% is reabsorbed by the renal tubules
• <10% of the total are excreted through the gastrointestinal tract and skin
Plasma BUN Concentration is determined by:
- Renal function
- Dietary protein intake
- Protein catabolism rate
[Clinical significance of BUN)
Measurement of urea is used to:
- Evaluate renal function
- Assess hydration status
- Determine nitrogen balance
- Aid in the diagnosis of renal disease
- Verify adequacy of dialysis
Pre-renal causes (ie blood vessels) of Hyperuremia or increased BUN
(Sometimes translates into dehydration) • ↓ Renal blood flow (e.g. CHF & dehydration) • ↑ Protein catabolism (as in fever) • High protein diet • Corticosteroid drugs
Renal/within the kidney causes of hyperuremia have usually what
Co-morbidity with other diseases
Renal causes of HYPERUREMIA
- Acute and chronic renal failure (associated with diabetes mellitus)
- Glomerular nephritis
- Tubular necrosis
- Malignant hypertension
Post-renal (outside the kidney) causes of HYPERUREMIA are usually associated with
Obstruction: • Urethral stones • Tumors of bladder • Prostate enlargement • Cervical cancer
A decrease in BUN is associated with
Hypouremia
Symptoms of hypouremia
- Liver failure or severe liver disease (lack of urea synthesis)
- Severe vomiting and/or diarrhea
- Decreased dietary protein
- Increased protein synthesis (observed in pregnant women and children)
- Malnutrition (e.g. Kwashiorkor)
- Overhydration
- Early and late stages of pregnancy
It is the elevated urea concentration in blood (>20mg/dL)
Azotemia
T or F: Azotemia is always due to kidney dysfunction
False
Very high plasma urea concentration accompanied with renal failure
Uremic Syndrome or Uremia
• Urea crosses the blood-brain barrier which is used by the brain for energy (Leads to confusion, lethargy, and comatose)
• Uremic pericarditis: presence of heart murmurs
What is the mechanism of azotemia in pre-renal causes?
Reduced renal blood flow > less blood is delivered to the kidney > less urea filtered
(Anything that causes a decrease in functional blood volume (low blood pressure))
Pre-renal causes of AZOTEMIA
- Congestive heart failure
- Shock
- Hemorrhage
- Dehydration
- High-protein diet
- Increased catabolic states (e.g. fever, major illness, stress)
Why does decreased renal function (glomerular filtration) lead to increased blood urea?
Poor excretion
Renal causes of AZOTEMIA
- Acute & chronic renal failure
- Glomerulonephritis
- Nephrotic syndrome
- Tubular necrosis
- Other intrinsic renal diseases
Post-renal causes of AZOTEMIA are usually due to
Obstruction of renal flow (renal calculi/kidney stones)
• Tumors of the bladder or prostate
• Severe infections (UTI)
T or F: BUN is more susceptible to non-renal functions
True
Reference ranges for BUN
Reference range: 7–18 mg/dL
Specimen requirements for BUN
- Plasma
- Serum
- 24-hour Urine Collection
- Non-hemolyzed (Hemolysis can increase BUN)
Methods used for BUN
Kjeldahl method (classical, measures nitrogen) Berthelot reaction (manual, uses urease to split off ammonia and produce color rxn) Diacetyl monoxide (or monoxime) (popular but not manual, uses strong acids and oxidizing chemicals
How is BUN converted to urea?
Urea nitrogen concentration can be converted to urea concentration by multiplying by 2.14
(See trans for example)
Methodology for conversion of BUN to urea
- Enzymatic (Most common method that couples the urease reaction with glutamate dehydrogenase, see trans)
- Indicator Dye (Addition of PH indicator to ammonium ion results to color change)
- Conductimetric (Conversion of unionized urea to NH4+ and CO32- results in increased conductivity)
Reference Range of Urea N
- Serum or Plasma: 6–20 mg/dL
* 24 hours urine: 12–20 grams/day
(See trans for bun/creatinine ratio)
(See trans for bun/creatinine ratio)
What are the sources of creatine in the liver?
arginine, glycine, and methionine
Creatine is converted to
Creatine phosphate (High energy source for muscle tissues)
Where does creatinINe come from?
produced as a waste product of creatine and creatine phosphate in muscles
Creatine Phosphate – Phosphoric Acid = Creatinine
Creatine – Water = Creatinine
When is creatine elevated in plasma and urine?
muscular dystrophy, hyperthyroidism, trauma
Specialized testing; not part of routine lab
Internal anhydride derived from dephosphorylation of creatine phosphate and a metabolic product cleared entirely by the glomerular filtration
Creatinine
T or F: creatinine is not reabsorbed
True
Neither secreted nor absorbed by renal tubules
What must happen in order to see increased creatinine in serum?
50% kidney function is lost
What affects creatinine?
Creatinine levels are affected by muscle mass, creatine turnover, and renal function
(Released into circulation at a stable rate proportional to muscle mass; excreted in urine)