Presentation on theme: "CLINICAL CHEMISTRY CHAPTER 9"— Presentation transcript:
1 CLINICAL CHEMISTRY CHAPTER 9 NON - PROTEIN NITROGEN
2 IntroductionNPN ( Non - Protein Nitrogen ) is a “funky” term that can be used for a bunch of different substances that have the element nitrogen in them, but are not proteins.This is a little unusual, because most of the body’s nitrogen is associated with proteins.There are many different unrelated NPNs, but we are only interested in 4 of them:Creatinine , Blood Urea Nitrogen ( BUN ) , Uric Acid and AmmoniaIn general, plasma NPNs are increased in renal failure and are commonly ordered as blood tests to check renal function
4 ObjectivesList the origin and principle clinical significance of BUN, Creatinine, Uric Acid and AmmoniaList the reference ranges for the 4 principle NPNsDiscuss why creatinine is the most useful NPN to evaluate renal functionCalculate Creatinine ClearanceDiscuss the common methodologies used to measure BUN, Creatinine, Uric Acid and Ammonia
5 General ideas about the NPNs Antiquated term when protein – free filtrates were required for testingThe NPNs were used for evaluating renal functionThe NPNs include about 15 different substancesMost NPNs are derived from protein or nucleic acid catabolismMost important NPNsBUN ( Blood Urea Nitrogen )CreatinineUric acidAmmonia
6 Urea BUN ( Blood Urea Nitrogen ) Blood Urea Nitrogen = BUN = Urea 50% of the NPNsProduct of protein catabolism which produces ammoniaAmmonia is very toxic – converted to urea by the liverLiver converts ammonia and CO2Filtered by the glomerulus but also reabsorbed by renal tubules ( 40 % )Some is lost through the skin and the GI tract ( < 10 % )Plasma BUN is affected byRenal functionDietary proteinProtein catabolismUrea
7 BUN disease correlations Azotemia = Elevated plasma BUNPrerenal BUN ( Not related to renal function )Low Blood Pressure ( CHF, Shock, hemorrhage, dehydration )Decreased blood flow to kidney = No filtrationIncreased dietary protein or protein catabolismPrerenal BUN ( Not related to renal function )Decreased dietary proteinIncreased protein synthesis ( Pregnant women , children )
8 Renal disease with decreased glomerular filtration Renal causes of BUNRenal disease with decreased glomerular filtrationGlomerular nephritisRenal failure form Diabetes MellitusPost renal causes of BUN ( not related to renal function )Obstruction of urine flowKidney stonesBladder or prostate tumorsUTIs
9 BUN / Creatinine RatioNormal BUN / Creatinine ratio is 10 – 20 to 1Creatinine is another NPNPre-renal increased BUN / Creat ratioBUN is more susceptible to non-renal factorsPost-renal increased ratio BUN / Creat ratioBoth BUN and Creat are elevatedRenal decreased BUN / Creat ratioLow dietary protein or severe liver disease
10 BUN analytical methods BUN is an old term, but still in common use Specimen : Plasma or serumTo convert BUN to Urea : BUN x = Urea ( mg / dl )Urease2 NH HCO3-UREAGLDHNH OXOGLUTARATEGLUTAMATENADHNADMeasure the rate of decreased absorbance at 340 nmNADH absorbs … NAD does not absorbReference range : – 20 mg / dl
11 Liver Amino Acids Creatine Muscles Creatine Phosphocreatine CREATININELiver Amino Acids CreatineMuscles Creatine PhosphocreatineMuscles Phosphocreatine CreatinineCreatinine formed at a constant rate by the muscles as a function of muscle massCreatinine is removed from the plasma by glomerular filtrationCreatinine is not secreted or absorbed by the renal tubulesTherefore : Plasma creatinine is a function of glomerular filtrationUnaffected by other factorsIt’s a very good test to evaluate renal function
12 Creatinine disease correlations Increased plasma creatinine associated with decreased glomerular filtration ( renal function )Glomerular filtration may be 50 % of normal before plasma creatinine is elevatedPlasma creatinine is unaffected by dietPlasma creatinine is the most common test used to evaluate renal functionPlasma creatinine concentrations are very stable from day to day - If there is a delta check , its very suspicious and must be investigated
13 Creatinine analytical techniques Jaffee Method ( the Classic technique )Creatinine + Picrate Acid Colored chromogenSpecimen : Plasma or serumElevated bilirubin and hemolysis causes falsely decreased resultsReference range : mg / dl
14 URIC ACIDBreakdown product of purines ( nucleic acid / DNA )Purines from cellular breakdown are converted to uric acid by the liverUric acid is filtered by the glomerulus ( but 98 – 100 % reabsorbed )Elevated plasma uric acid can promote formation of solid uric acid crystals in joints and urine
15 Uric acid diseases Gout Increased plasma uric acid Painful uric acid crystals in jointsUsually in older males ( > 30 years-old )Associated with alcohol consumptionUric acid may also form kidney stonesOther causes of increased uric acidLeukemias and lymphomas ( DNA catabolism )Megaloblastic anemias ( DNA catabolism )Renal disease ( but not very specific )
16 + Uric acid analysis Uricase Uric acid + O2 + H2O Allantoin + CO2 H2O2 Uric acid absorbs light @ 293 nm , Allantoin does not.The rate of decreased absorption is proportional to the uric acid concentration.Specimen : Plasma or serumReference range : mg/dl (males)mg/dl (females)Let’s remember mg/dl
17 Ammonia is very toxic - The liver converts ammonia into urea Produced from the deamaination of amino acids in the muscle and from bacteria in the GI tractAmmonia is very toxic - The liver converts ammonia into ureaUrea is less toxic and can be removed from the plasma by the kidneysIn severe hepatic disease, the liver fails to convert ammonia into urea, resulting in increased plasma ammonia levelsIncreased plasma ammonia concentrations in :Liver failureReye’s Disease
18 Ammonia analytical techniques NH OXOGLUTARATE + NADPH L-GLUTAMATE +NADP+There is a decreasing nm, proportional to the ammonia concentration.Specimen : EDTA or Heparinized Whole Blood on iceMust be tested ASAP or plasma frozenDelayed testing caused false increased valuesReference range : 20 – 60 µg / dl
19 Creatinine is an endogenous substance ( not affected by diet ) Creatinine ClearanceCalculated measurement of the rate at which creatinine is removed from the plasma by the kidneysMeasurement of glomerular filtration ( renal function )A good test of glomerular filtration becauseCreatinine is an endogenous substance ( not affected by diet )Creatinine is filtered by the glomerulus, but not secreted or re-absorbed by the renal tubules
20 24 Hour Urine collectionContainer.The volume can be measureddirectly off the container.
21 Creatinine Clearance specimens 24 hour urine specimenPlasma / serum creatinine collected during the urine collection24 Hour Creatinine Clearance FormulaCREATININE CLEARANCE =U = Creatinine concentration of the 24 hour urine ( mg / dl )V = hour urine volume ( mls ) per minute V / 1440 = mls / minuteP = Plasma creatinine concentration ( mg / dl )A = Correction factor accounts for differences in body surface areaobtained from a height – weight chart
22 Example of a 24 Hour Creatinine Clearance calculation 24 hour urine volume = mls24 hour urine creatinine = mg / dlPlasma creatinine = mg / dlPatients height / weight = 6’00 / lbs ( see pg. 680 )Creat Cl = ml / min …. Very poor clearance !!!
23 Procedure for 24 Hour Urine Collection Have the patient empty his / her bladder ( discard this urine ).Note the time . For the next 24 hours, have the patient collect and save all urine in an appropriate container.At the end of the 24 hour period have the patient void one last time into the urine container. This completes the collection.If possible, keep the urine specimen refrigerated.
24 Reference rangeml / min ( male)ml / min (female)Let’s remember ml / min
25 NPN TOP 10 Increased Creatinine associated with renal failure Increased BUN associated with renal failure and protein catabolismIncreased Uric Acid associated with GoutIncreased Ammonia is associated with liver diseaseCreatinine derived from cellular creatine … very constant from day to dayDelta checks on plasma Creatinine must be investigated !!!BUN ( Urea ) is derived from protein catabolismProtein Ammonia UreaUric Acid is derived from purine( a component of DNA ) catabolismDecreased Creatinine Clearance associated with decreased Glomerular FiltrationDon’t forget to divide V by 1440 !
26 Reference Ranges BUN 10 - 20 mg / dl Creatinine 0.5 - 1.5 mg /dl Uric Acid mg / dlCreatinine Clearance ml / minAmmonia ug / dlBUN / Creat Ratio to 1