Non-Protein Nitrogen(NPN) Compounds

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

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

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

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

14. 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: 6-20 mg/dl 24 hours Urine: 12-20 g/day