1. Non-Protein Nitrogen(NPN) Compounds
UG3, Semester 5
Clinical Biochemistry
Lecture 3
Non-Protein Nitrogen(NPN) Compounds

2. Non-protein Nitrogen Compounds
The determination of nonprotein nitrogenous substances in the blood has traditionally been used to monitor renal function.
Nitrogen containing compounds that are not proteins or polypeptides
Useful clinical information is obtained from individual components of NPN fraction

3. Clinically Significant NPN
The NPN fraction comprises about 15 compounds
Majority of these compounds arise from catabolism of proteins and nucleic acids

4. Urea Nitrogen (Blood) BUN
Highest concentration of NPN in blood
Major excretory product of protein metabolism
These processes release nitrogen, which is converted to ammonia
Synthesized in the liver from CO2 and Ammonia that arises from deamination of amino acids
Organisms synthesize urea from ammonia because ammonia (a common metabolic waste product) raises pH in cells to toxic levels. Therefore, urea synthesis is necessary even though it costs energy to produce. Urea is neither acidic nor basic, so it is a perfect vehicle for getting rid of nitrogen waste

5. Urea Nitrogen (Blood) BUN
Assays for urea were based on measurement of nitrogen, the term blood urea nitrogen (BUN) has been used to refer to urea determination.
Excreted by the kidneys – 40% reabsorbed
<10% of the total are excreted through the gastrointestinal tract and skin.
Concentration is determined by:
Renal function
Dietary intake
Protein catabolism rate

6. Clinical Application Measurement of urea is used to:
evaluate renal function,
to assess hydration status,
to determine nitrogen balance,
to aid in the diagnosis of renal disease,
and to verify adequacy of dialysis.

7. Disease Correlations Azotemia: elevated conc. of urea in blood
Very high plasma urea concentration accompanied by renal failure is called uremia, or the uremic syndrome
Causes of urea plasma elevations are:
Prerenal
Renal
and postrenal

8. Pre-Renal Azotemia
Reduced renal blood flow Less blood is delivered to the kidney less urea filtered
Anything that produces a decrease in functional blood volume, include:
Congestive heart failure,
shock,
hemorrhage,
dehydration
High protein diet or increased catabolism (Fever, major illness, stress)

9. Renal Azotemia
Decreased renal function causes increased blood urea due to poor excretion
Acute & Chronic renal failure
Glomerular nephritis
Tubular necrosis
& other Intrinsic renal disease
Glomerulonephritis, also known as glomerular nephritis, abbreviated GN, is a renal disease characterized by inflammation of the glomeruli, or small blood vessels in the kidneys

10. Post-Renal Azotemia Obstruction of urine flow
Renal calculi
Tumors of bladder or prostate
Severe infections

11. Decreased Urea Nitrogen
Low protein dietary intake
Liver disease (lack of synthesis)
Severe vomiting and/or diarrhea (loss)
Increase protein synthesis

12. Analytical methods
Assays for urea were based on measuring the amount of nitrogen in the sample (BUN)
Current analytic methods have retained this custom and urea often is reported in terms of nitrogen concentration rather than urea concentration (urea nitrogen).
Urea nitrogen concentration can be converted to urea concentration by multiplying by 2.14

13. Conversion of BUN to urea
Atomic mass of nitrogen = 14 g/mol;
Molecular mass of urea = g/mol.
Urea contains two nitrogen atoms per molecule.
Urea nitrogen (urea N) is 46.6% by weight of urea (28 divided by 60.06).
Therefore: 10 mg/dL of BUN divided by = mg/dL of urea

14. Analytical methods Enzymatic
Urease → hydrolysis of urea to ammonium ion , then detect ammonium ion (NH4+)
Enzymatic
The most common method couples the urease reaction with glutamate dehydrogenase
glutamate dehydrogenase = GLDH

15. NH4+ + pH indicator → color change
Analytical methods
Indicator dye
NH4+ + pH indicator → color change
Conductimetric
Conversion of unionized urea to NH4+ and CO32- results in increased conductivity
Reference range of Urea N:
Serum or plasma: mg/dl
24 hours Urine: g/day :