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CC finals readings > NPN/urea > Flashcards

NPN/urea Flashcards

1
Q

originated in the early days of clinical chemistry when analytic methodology required removal of protein from a specimen before analysis

A

nonprotein nitrogen (NPN)

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2
Q

The concentration of nitrogen-containing compounds in this protein-free filtrate was quantified spectrophotometrically by converting nitrogen to ammonia and subsequent reaction with

A

Nessler’s reagent (K2[HgI4]) to produce a yellow color

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3
Q

this method was technically difficult but provided an accurate determination of total NPN concentration

A

Nessler’s reagent (K2[HgI4])

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4
Q

-NPN compound present in highest concentration in the blood
-major excretory product of protein metabolism
-formed in the liver from amino groups (−NH2) and free ammonia generated during protein catabolism

A

urea

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5
Q

-historic assays for urea were based on the measurement of nitrogen
-used to refer to urea determination

A

blood urea nitrogen (BUN)

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6
Q

more appropriate term

A

Urea nitrogen (urea N)

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7
Q

produces amino acids that can be oxidized to produce energy or stored as fat and glycogen

A

Protein metabolism

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8
Q

-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
-originally performed on a protein-free filtrate of whole blood and based on measuring the amount of nitrogen

A

Measurements of urea

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9
Q

can be converted to urea concentration by multiplying by 2.14

A

Urea N concentration

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10
Q

International System of Units (SI), urea is reported in units of

A

millimoles per liter

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11
Q

Urea N concentration in milligrams per deciliter may be converted to urea concentration in millimoles per liter by multiplying by

A

0.36

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12
Q

most frequently in clinical laboratories

A

Enzymatic methods

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13
Q

catalyzes hydrolysis of urea in the sample

A

enzyme urease (urea amidohydrolase, EC 3.5.1.5)

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14
Q

produced in the reaction is quantified

A

ammonium ion

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15
Q

most common method couples the urease reaction with glutamate dehydrogenase (GLDH, EC 1.4.1.3), and the rate of disappearance of nicotinamide adenine dinucleotide (reduced, NADH) at ____ nm is measured

A

340

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16
Q

from the urease reaction can also be measured by the color change associated with a pH indicator

A

Ammonium

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17
Q

reference method

A

isotope dilution mass spectrometry (IDMS)

18
Q

Urea concentration may be measured in

A

plasma, serum, or urine

19
Q

If plasma is collected, ammonium ions and high concentrations of sodium citrate and sodium fluoride must be avoided;

A

citrate and fluoride inhibit urease

20
Q

Urea is susceptible to bacterial decomposition, so specimens (particularly urine) that cannot be analyzed within a few hours should be

A

refrigerated

21
Q

should be refrigerated during the collection period

A

Timed urine specimens

22
Q

require modification for use with urine specimens because of high urea concentration and the presence of endogenous ammonia

A

Methods for plasma or serum

23
Q

elevated concentration of urea in the blood

A

azotemia

24
Q

-Very high plasma urea concentration accompanied by renal failure
-This condition is eventually fatal if not treated by dialysis or transplantation

A

uremia/uremic syndrome

25
Q

result of reduced renal blood flow. Less blood is delivered to the kidney; consequently, less urea is filtered.

A

Prerenal azotemia

26
Q

Prerenal azotemia Causative factors include

A

congestive heart failure,
shock,
hemorrhage,
dehydration,
and other
factors resulting in a significant decrease in blood volume

27
Q

The amount of protein metabolism also induces prerenal changes in blood urea concentration. A high-protein diet or increased protein catabolism, such as

A

occurs in stress,
fever,
major illness,
corticosteroid therapy, and
GI hemorrhage, may increase the urea concentration.

28
Q

causes an increase in plasma urea concentration as a result of compromised urea excretion

A

Decreased renal function

29
Q

causes of elevated urea include acute and chronic renal failure, glomerular nephritis, tubular necrosis, and other intrinsic renal disease

A

Renal

30
Q

can be due to obstruction of urine flow anywhere in the urinary tract by renal calculi, tumors of the bladder or prostate, or severe infection

A

Postrenal azotemia

31
Q

major causes of decreased plasma urea concentration

A

low protein intake and severe liver disease

32
Q

Plasma urea concentration is decreased during late _______ ________ as a result of increased protein synthesis

A

pregnancy and in infancy

33
Q

Differentiation of the cause of abnormal urea concentration is aided by calculation of the urea nitrogen/creatinine (urea N/creatinine) ratio, which is

A

normally 10:1 to 20:1

34
Q

tend to elevate plasma urea, whereas plasma creatinine remains normal, causing a high urea N/creatinine ratio

A

Prerenal conditions

35
Q

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

A

postrenal conditions

36
Q

low urea N/creatinine ratio is observed in conditions associated with decreased urea production, such as

A

low protein intake, acute tubular necrosis, and severe liver disease

37
Q

Decreased urea Concentration

A

Low protein intake
Severe vomiting and diarrhea
Liver disease
Pregnancy

38
Q

Increased urea Concentration

A

Prerenal
Renal
Postrenal

39
Q

Prerenal

A

congestive heart failure
Shock, hemorrhage
Dehydration
Increased protein catabolism
High-protein diet

40
Q

Renal

A

Acute and chronic renal failure
Renal disease, including glomerular nephritis and tubular necrosis

41
Q

Postrenal

A

Urinary tract obstruction

CC finals readings (16 decks)

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