Bishop Chapter 12 Nonprotein Nitrogen Compounds Flashcards
What NPN compound is present in the highest concentration in the blood?
Urea.
Protein metabolism produces amino acids that release what by-product?
Nitrogen.
Following synthesis in the liver, urea is carried where?
By the blood to the kidney, where it is readily filter from the plasma by the glomerulus.
The concentration of urea in the plasma is determined by what?
Protein content of the diet, the rate of protein catabolism, and renal function and perfusion.
What is the importance of urea measurement?
Used to evaluate renal function, assess hydration status, determine nitrogen balance, aid in renal disease Dx, and to verify adequacy of dialysis.
Concentration of what element is urea reported?
Concentration of Nitrogen.
Urea nitrogen concentration can be converted to urea concentration by multiplying by what?
2.14.
What analytical methods are most commonly used to assay urea?
Enzymatic methods.
What is the methodology of enzymatic methods that use a similar first step - catalyze by urease?
Enzymatic production of ammonium ion (NH4+) from urea.
What is the methodology of the GLDH-coupled enzymatic method?
Enzymatic reaction of NH4+, 2-oxoglutarate, and NADH to form glutamate and NAD+.
What is the methodology of the indicator dye enzymatic method?
NH4+ + pH indicator –> color change
What is the methodology of the conductometric enzymatic method?
Conversion of unionized urea to ammonium and carbonate results in increased conductivity.
What is the methodology of the isotope dilution mass spectrometry method?
Detection of characteristic fragments following ionization; quantification using isotopically labeled compounds.
Urea concentration may be measured in what types of samples?
Plasma, serum, or urine.
Why should sodium citrate and sodium fluoride tubes be avoided?
Citrate and fluoride inhibit urease.
Why should urine specimens be refrigerated if not analyzed within a few hours?
Urea is susceptible to bacterial decomposition.
Define azotemia.
Elevated concentration of urea in the blood.
Define uremia/uremic syndrome.
Very high plasma urea concentration accompanied by renal failure.
Conditions causing increased plasma urea are classified according to the cause into what three categories?
Prerenal, renal, and postrenal.
Prerenal azotemia is a result of what?
Reduced renal blood flow.
What are the main causes of decreased plasma urea concentration?
Low protein intake and severe liver disease.
What is considered normal for a urea nitrogen/creatinine (urea N/creatinine) ratio?
Between 10:1 to 20:1.
A high urea N/creatinine ratio with an elevated creatinine is usually seen where?
In postrenal conditions.
A low urea N/creatinine ratio is usually observed in conditions associated with decreased urea production, what conditions would this include?
Low protein intake, acute tubular necrosis, and severe liver disease.
Uric acid is product of what process?
Catabolism of the purine nucleic acids.
Nearly all of the uric acid in plasma is present as what?
Monosodium urate.
Uric acid is measured to confirm diagnosis and monitor the treatment of what condition?
Gout.
What are the most common and most specific methods for uric acid measurement?
Methods using uricase, the enzyme that catalyzes the oxidation of uric acid to allantoin.
At what absorption is uric acid and allantoin measured?
293 nm.
Uric acid concentration may be measured in what types of samples?
Heparinized plasma, serum, or urine.
How does a high bilirubin affect uric acid measurements?
May falsely decrease results obtained by peroxidase methods.
What drugs have been shown to increase values for uric acid?
Salicylates and Thiazides.
What should the urine pH be when measuring uric acid?
pH 8.0.
Define hyperuricemia.
Overproduction of uric acid.
How are uric acid measurements effected by a patient with hemolytic or megaloblastic anemia?
May exhibit elevated uric acid concentration.
Why does chronic renal disease cause elevated uric acid concentrations?
Because filtration and secretion are impaired.
Hypouricemia is usually secondary to what condition(s)?
Severe liver disease or defective tubular reabsorption.
How is creatinine formed?
Creatinine is formed from creatine and creatine phosphate in muscle and is excreted into the plasma at a constant rate related to muscle mass.
Plasma creatinine is inversely related to ___.
Glomerular filtration rate (GFR).
What three amino acids form creatine?
Arginine, glycine, and methionine.
What does creatinine clearance (CrCl) measure?
It measures the amount of creatinine eliminated from the blood by the kidneys; used to gauge renal function.
What are acceptable samples to test for creatinine?
Plasma, serum, or urine.
What types of samples should be avoided if testing for creatinine?
Hemolyzed, icteric, and lipemic.
When plasma creatinine concentration is elevated, and GFR is decreased, what does that indicate?
Renal damage.
In what conditions is both plasma creatine and urinary creatinine often elevated?
Muscular dystrophy, poliomyelitis, hyperthyroidism, and trauma.
Plasma creatine concentration is NOT elevated in what condition(s)?
Renal disease.
How is ammonia produced?
In the deamination (removal of amino group) of amino acids during protein metabolism.
Ammonia is removed from the circulation and converted to ___ in the liver.
Urea.
What biochemical process is ammonia consumed?
The Krebs or Urea cycle.
What condition(s) is blood ammonia concentration provides useful information?
Hepatic failure, Reye’s syndrome (acute metabolic disorder of the liver), inherited deficiencies of urea cycle enzymes.
What is the most common method for ammonia determination?
An enzymatic method using glutamate dehydrogenase.
At what absorbance is NADPH consumed and becomes equally proportional to ammonia concentration?
340 nm.
How should a blood sample for ammonia be collected.
Venous blood (without trauma) and placed on ice immediately.
What is done by the patient that can cause a significant source of ammonia contamination?
Cigarette smoking.
In what conditions is ammonia not removed from the circulation therefore increases in blood concentration?
Severe liver disease.
