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nonprotein nitrogens
clinically significant non-protein nitrogens
| Question | Answer |
|---|---|
| What has the determination of npn in the blood been used to monitor? | renal function |
| Concentration of nitrogen containing compounds was measured spectrophotometrically by converting nitrogen to ammonia and subsequent reaction with what reagent to form what color? | Nessler's reagent. Yellow color. |
| NPN are the products of what types of catabolism? | protein and nucleic acid |
| NPN in highest concentration in blood? | Urea |
| Excretory product of protein and AA metabolism | Urea |
| Synthesized in liver from ammonia and CO2 from the deamination of AA in urea cycle? | Urea |
| Filtered by the glomerulus. 40% reabsorbed in tubules. | Urea |
| Amount of urea reabsorbed depends on what? | Urine flow rate and hydration |
| Conversion of BUN to urea | multiply by 2.14 |
| How much nitrogen does 60 grams of urea contain? | 28 grams nitrogen |
| Refers to elevated levels of urea in the blood | azotemia |
| Refers to high levels of urea accompanied by renal failure | uremia |
| Pre-renal causes of azotemia | Reduced blood flow->less urea filtered dehydration, shock, corticosteroid therapy, high protein diet, fever, CHF |
| Renal causes of azotemia | decreased renal function. glomerular-nephritis, tubular necrosis, chronic renal failure, intrinsic renal disease. |
| Post-renal causes of azotemia | urinary tract obstruction - stones, tumor, severe infection |
| Causes of decreased plasma urea | decreased protein intake, late pregnancy, infancy, severe liver disease |
| Tests used to differentiate the cause of azotemia | BUN and Creatinine |
| Normal BUN:Creatinine ratio | 10:1 - 20:1 |
| Pre-renal conditions have what levels of BUN and Creatinine. What ratio? | increased BUN, Normal Creatinine. High BUN:Creatinine ratio |
| Post-renal conditions have what levels of BUN and Creat? What ratio? | increased BUN, increased Creat. High ratio. |
| Conditions resulting in decreased BUN:Creat ratio | decreased urea production. decreased protein intake, tubular necrosis, liver disease |
| First step in enzymatic methods for urea | conversion of urea to ammonia in presence of urease |
| Glutamate dehydrogenase (GLDH) coupled reaction for urea | kinetic method that measures rate of disappearance of NADH at 340nm. |
| NH4 + 2-oxoglutarate + NADH -> Glutamate +H2O + NAD+ | GLDH coupled enzymatic reaction for urea |
| NH3+ + pH indicator -> color change | indicator dye method for urea |
| Conductometric method for urea | conversion of unionized urea to NH4+ and HCO3- results in decreased conductivity. Specific and Rapid. |
| Advantages of conductometric method | specific and rapid. ammonia does not interfere. |
| NH4+ + 5NaOCl + 2phenol -(nitroprusside/OH-)-> indophenol + 5NaCl + 5H2O -indophenol colored. | Berthelot Method for urea |
| What are disadvantages to Berthelot method? | Non-specific. Sensitive to interference from endogenous ammonia. |
| Measurement of urea by condensation with diacetyl monoxime in the presence of a strong acid and an oxidizing agent. | Forms diazine which is yellow and is measured at 540 nm |
| Disadvantages of diacetyl monoxime method / advantages | toxic reagents, non-specific ammonia does not interfere. |
| o-Phthaldehyde and naphthylethylenediamine react with what to form a chromogen? | urea |
| Proposed definitive method for urea | isotope-dilution mass spectrometry |
| Reference method for urea | urease/GLDH coupled enzymatic reaction |
| What inhibits urease and should be avoided for specimen collection? | sodium citrate and sodium fluoride |
| Why should specimens for urea analysis be refrigerated? | Urea is susceptible to bacterial composition |
| Specimens for urea concentrations | plasma, serum, or urine |
| Reference ranges for BUN serum and urine | 6-20 mg/dL and 12 - 20 g/day. |
| conversion of mg/dL to mmol/L | multiply by 0.36 |
| Who has slightly higher levels of urea? | adults over 60 and males |
| Who has slightly lower urea levels? | pregnant women and children |
| Synthesized in the liver from arginine, glycine and methionine | creatine |
| What is creatine converted to after being transported to muscle and what is it good for? What enzyme involved? | phosphocreatine - high energy source for muscle building. Creatine Kinase |
| How much creatine is converted to creatinine daily? | 2% |
| Waste product of muscle metabolism | creatinine |
| What is formed when creatine phosphate loses phosphoric acid or when creatine loses water. | creatinine |
| How is creatinine excreted? | filtered by glomerulus and excreted in urine |
| What is plasma creatinine conc. a function of? | muscle mass, creatine turnover, and renal function |
| Causes of increased plasma and urine creatine | muscular dystrophy, polio, hyperthyroidism, trauma |
| Is creatinine elevated in cases of increased creatine? | creatinine is normal |
| Are plasma creatine levels elevated in renal disease? | NO |
| Are serum creatinine levels affected by a high protein diet? Muscle mass? | NO. Yes, proportional to muscle mass. |
| Why is Creatinine is a reliable indicator of kidney function as it relates to glomerular function? | 1) It's filtered completely through glomerulus and not reabsorbed by nephron tubule 2) It's an endogenous substance |
| measure of the ability of the glomerulus to filter blood | creatinine clearance |
| Equation for creatinine clearance | urine creat x urine vol / plasma creat x 1440 |
| correction factor for body mass | x 1.73/A |
| plasma conc of creatinine is ______ to creatinine clearance | inversely proportional |
| Reference Ranges for Creatinine Clearance | Male: 97-137 mL/min per 1.73 m2 Female: 88-128 mL/min per 1.73 m2 |
| What is the Jaffe reaction | based on principle that creatinine reacts with picrate in an alkaline soln to form an orange-red complex. |
| Disadvantages of Jaffe | nonspecific and subject to positive interference from acetoacetate, acetone, glucose, ascorbate,pyruvate, cephalosporins |
| Adsorbent for jaffe | Fuller's Earth or lloyds reagent |
| Dry slide method for creatinine | coupled enzymatic reaction using creatininase, creatinase, sarcosine oxidase, and peroxidase. |
| method for creatinine using reagent strip | 3,5-dinitrobenzoic acid (DNBA) + creatinine = purple product |
| Interferences of dry slide method | some + due to lidocaine. Not affected by acetoacetate or cephalosporins. |
| Proposed reference method for creatinine | HPLC |
| Specimen collection for creatinine | plasma, serum, or urine. Avoid hemolysis and icterus (esp Jaffe), refrig urine and adjust to pH 7 |
| Major product of purine metabolism | uric acid |
| where is uric acid synthesized and where excreted | liver adn kidney |
| what form is nearly all uric acid in plasma | monosodium urate ions |
| At what conc can urate in plasma form crystals and precipitate? | >6.4 mg/dL |
| Disease states associated with hyperuricemia | gout, increased metabolism of cell nuclei(chemotherapy), renal disease, hemolytic/megaloblastic anemia, Lesch-Nyhan syndrome, dietary intake of purines, G6PD def, toxemia of pregnancy and lactic acidosis |
| Clinical Significance of hypouricemia | secondary to liver disease ro defective tubular reabsorption (Fanconi's syndrome), chemo with 6-mercaptopurine or azathioprine. Overtreatment with allopurinol |
| uric acid is readily oxidized to what in the presence of what | allantoin in the presence of uricase |
| caraway method for urea | oxidation of uric acid with subsequent reduction of phosphotungstic acid to tungsten blue at 650-700 nm. Lacks specificity. |
| what provides alkaline pH for phosphotungstic method | sodium carbonate |
| spectrophotometric method for uric acid using uricase | measures decrease in absorbance at 293 nm as uric acid is converted to allantoin by uricase |
| interferences in simple uricase method | proteins reduce sensitivity. Neg interference from hemoglobin and xanthine |
| Coupled enzymatic reactions for uric acid | measure hydrogen peroxide produced as uric acid is converted to allantoin. |
| What catalyzes the indicator reaction in uric acid coupled reactions | peroxidase or catalase |
| Interference in peroxide coupled reactions | bilirubin and ascorbic acid destroy peroxide. minimize with potassium ferricyanide or ascorbate oxidase |
| Uric Acid Ref Ranges Male: | 3.5 - 7.2 mg/dL |
| Uric Acid Female | 2.6 - 6.0 mg/dL |
| uric acid child | 2.0 - 5.5 mg/dL |
| uric acid 24hr urine | 250 - 750 mg/dL |
| uric acid increase or decrease with age, pregnancy, children, premenopause | increase,increase,decrease,decrease |
| Specimen for uric acid | plasma, serum, urine. separate from RBCs ASAP |
| Falsley increase uric acid | salicylates and thiazides |
| Falsely decrease uric acid | hemolysis, icterus |
| Deamination product of AAs due to work of digestive and bacterial enzymes on proteins in GI Tract | Ammonia |
| Released from skeletal muscle in exercise | ammonia |
| what happens to ammonia in liver | consumed by parenchymal cells in production of urea |
| are plasma ammonia conc dependent on renal function | no |
| what are high levels of ammonia associated with | being neurotoxic and associated with encephalopathy |
| what is ammonia conc useful for | monitoring progress of severe clinical conditions |
| High levels of ammonia seen in | liver disease, Reye's syndrome (children treated with asprin for virus), Renal failure, inherited defects in urea cycle |
| all enzymes in urea cycle are deficient in inherited disorders except for | argininosuccinase |
| ion exchange method for ammonia | NH3 adsorbed onto Dowex 50 resin, eluted, and quantitated with Berthelot reagent |
| ISE method for ammonia | measures change in potential as pH of ammonium chloride soln as ammonia diffuses across membrane |
| Enzymatic method for ammonia | GLDH. measures decrease in absorbance at 340 nm as NADPH is reduced to NADP+ |
| Adult ammonia ref range | 11-35 umol/L plasma 10-107 mmol N/day |
| child ammonia range | 40 - 80 umol/L (higher than adults) |
| Specimen for ammonia | heparin or EDTA. Place on ice immediately. Centrifuge at 0-4C within 20min and remove plasma. Assay ASAP or freeze at -20C |
| errors causing increased Plasma ammonia levels | smoking,ammonium salts, asparginase, barbituates, diuretics, ethanol, analgesics, hemolysis |
| errors causing decreased plasma ammonia | diphenhydramine, lactobacillus acidophilus, levodopa, antibiotics |
| what causes reduction of nitrates to nitrites in urine | gram negative bacteria |
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