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MLS 411 Clinical Chemistry I > Bishop Chapter 12 Nonprotein Nitrogen Compounds > Flashcards

Bishop Chapter 12 Nonprotein Nitrogen Compounds Flashcards

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1
Q

What NPN compound is present in the highest concentration in the blood?

A

Urea.

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2
Q

Protein metabolism produces amino acids that release what by-product?

A

Nitrogen.

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3
Q

Following synthesis in the liver, urea is carried where?

A

By the blood to the kidney, where it is readily filter from the plasma by the glomerulus.

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4
Q

The concentration of urea in the plasma is determined by what?

A

Protein content of the diet, the rate of protein catabolism, and renal function and perfusion.

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5
Q

What is the importance of urea measurement?

A

Used to evaluate renal function, assess hydration status, determine nitrogen balance, aid in renal disease Dx, and to verify adequacy of dialysis.

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6
Q

Concentration of what element is urea reported?

A

Concentration of Nitrogen.

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7
Q

Urea nitrogen concentration can be converted to urea concentration by multiplying by what?

A

2.14.

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8
Q

What analytical methods are most commonly used to assay urea?

A

Enzymatic methods.

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9
Q

What is the methodology of enzymatic methods that use a similar first step - catalyze by urease?

A

Enzymatic production of ammonium ion (NH4+) from urea.

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10
Q

What is the methodology of the GLDH-coupled enzymatic method?

A

Enzymatic reaction of NH4+, 2-oxoglutarate, and NADH to form glutamate and NAD+.

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11
Q

What is the methodology of the indicator dye enzymatic method?

A

NH4+ + pH indicator –> color change

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12
Q

What is the methodology of the conductometric enzymatic method?

A

Conversion of unionized urea to ammonium and carbonate results in increased conductivity.

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13
Q

What is the methodology of the isotope dilution mass spectrometry method?

A

Detection of characteristic fragments following ionization; quantification using isotopically labeled compounds.

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14
Q

Urea concentration may be measured in what types of samples?

A

Plasma, serum, or urine.

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15
Q

Why should sodium citrate and sodium fluoride tubes be avoided?

A

Citrate and fluoride inhibit urease.

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16
Q

Why should urine specimens be refrigerated if not analyzed within a few hours?

A

Urea is susceptible to bacterial decomposition.

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17
Q

Define azotemia.

A

Elevated concentration of urea in the blood.

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18
Q

Define uremia/uremic syndrome.

A

Very high plasma urea concentration accompanied by renal failure.

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19
Q

Conditions causing increased plasma urea are classified according to the cause into what three categories?

A

Prerenal, renal, and postrenal.

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20
Q

Prerenal azotemia is a result of what?

A

Reduced renal blood flow.

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21
Q

What are the main causes of decreased plasma urea concentration?

A

Low protein intake and severe liver disease.

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22
Q

What is considered normal for a urea nitrogen/creatinine (urea N/creatinine) ratio?

A

Between 10:1 to 20:1.

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23
Q

A high urea N/creatinine ratio with an elevated creatinine is usually seen where?

A

In postrenal conditions.

24
Q

A low urea N/creatinine ratio is usually observed in conditions associated with decreased urea production, what conditions would this include?

A

Low protein intake, acute tubular necrosis, and severe liver disease.

25
Q

Uric acid is product of what process?

A

Catabolism of the purine nucleic acids.

26
Q

Nearly all of the uric acid in plasma is present as what?

A

Monosodium urate.

27
Q

Uric acid is measured to confirm diagnosis and monitor the treatment of what condition?

A

Gout.

28
Q

What are the most common and most specific methods for uric acid measurement?

A

Methods using uricase, the enzyme that catalyzes the oxidation of uric acid to allantoin.

29
Q

At what absorption is uric acid and allantoin measured?

A

293 nm.

30
Q

Uric acid concentration may be measured in what types of samples?

A

Heparinized plasma, serum, or urine.

31
Q

How does a high bilirubin affect uric acid measurements?

A

May falsely decrease results obtained by peroxidase methods.

32
Q

What drugs have been shown to increase values for uric acid?

A

Salicylates and Thiazides.

33
Q

What should the urine pH be when measuring uric acid?

A

pH 8.0.

34
Q

Define hyperuricemia.

A

Overproduction of uric acid.

35
Q

How are uric acid measurements effected by a patient with hemolytic or megaloblastic anemia?

A

May exhibit elevated uric acid concentration.

36
Q

Why does chronic renal disease cause elevated uric acid concentrations?

A

Because filtration and secretion are impaired.

37
Q

Hypouricemia is usually secondary to what condition(s)?

A

Severe liver disease or defective tubular reabsorption.

38
Q

How is creatinine formed?

A

Creatinine is formed from creatine and creatine phosphate in muscle and is excreted into the plasma at a constant rate related to muscle mass.

39
Q

Plasma creatinine is inversely related to ___.

A

Glomerular filtration rate (GFR).

40
Q

What three amino acids form creatine?

A

Arginine, glycine, and methionine.

41
Q

What does creatinine clearance (CrCl) measure?

A

It measures the amount of creatinine eliminated from the blood by the kidneys; used to gauge renal function.

42
Q

What are acceptable samples to test for creatinine?

A

Plasma, serum, or urine.

43
Q

What types of samples should be avoided if testing for creatinine?

A

Hemolyzed, icteric, and lipemic.

44
Q

When plasma creatinine concentration is elevated, and GFR is decreased, what does that indicate?

A

Renal damage.

45
Q

In what conditions is both plasma creatine and urinary creatinine often elevated?

A

Muscular dystrophy, poliomyelitis, hyperthyroidism, and trauma.

46
Q

Plasma creatine concentration is NOT elevated in what condition(s)?

A

Renal disease.

47
Q

How is ammonia produced?

A

In the deamination (removal of amino group) of amino acids during protein metabolism.

48
Q

Ammonia is removed from the circulation and converted to ___ in the liver.

A

Urea.

49
Q

What biochemical process is ammonia consumed?

A

The Krebs or Urea cycle.

50
Q

What condition(s) is blood ammonia concentration provides useful information?

A

Hepatic failure, Reye’s syndrome (acute metabolic disorder of the liver), inherited deficiencies of urea cycle enzymes.

51
Q

What is the most common method for ammonia determination?

A

An enzymatic method using glutamate dehydrogenase.

52
Q

At what absorbance is NADPH consumed and becomes equally proportional to ammonia concentration?

A

340 nm.

53
Q

How should a blood sample for ammonia be collected.

A

Venous blood (without trauma) and placed on ice immediately.

54
Q

What is done by the patient that can cause a significant source of ammonia contamination?

A

Cigarette smoking.

55
Q

In what conditions is ammonia not removed from the circulation therefore increases in blood concentration?

A

Severe liver disease.

MLS 411 Clinical Chemistry I (31 decks)

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