NPN/urea

Question 1

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

Answer 1

nonprotein nitrogen (NPN)

Question 2

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

Answer 2

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

Question 3

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

Answer 3

Nessler’s reagent (K2[HgI4])

Question 4

-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

Answer 4

urea

Question 5

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

Answer 5

blood urea nitrogen (BUN)

Question 6

more appropriate term

Answer 6

Urea nitrogen (urea N)

Question 7

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

Answer 7

Protein metabolism

Question 8

-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

Answer 8

Measurements of urea

Question 9

can be converted to urea concentration by multiplying by 2.14

Answer 9

Urea N concentration

Question 10

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

Answer 10

millimoles per liter

Question 11

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

Answer 11

0.36

Question 12

most frequently in clinical laboratories

Answer 12

Enzymatic methods

Question 13

catalyzes hydrolysis of urea in the sample

Answer 13

enzyme urease (urea amidohydrolase, EC 3.5.1.5)

Question 14

produced in the reaction is quantified

Answer 14

ammonium ion

Question 15

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

Answer 15

340

Question 16

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

Answer 16

Ammonium

Question 17

reference method

Answer 17

isotope dilution mass spectrometry (IDMS)

Question 18

Urea concentration may be measured in

Answer 18

plasma, serum, or urine

Question 19

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

Answer 19

citrate and fluoride inhibit urease

Question 20

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

Answer 20

refrigerated

Question 21

should be refrigerated during the collection period

Answer 21

Timed urine specimens

Question 22

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

Answer 22

Methods for plasma or serum

Question 23

elevated concentration of urea in the blood

Answer 23

azotemia

Question 24

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

Answer 24

uremia/uremic syndrome

Question 25

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

Answer 25

Prerenal azotemia

Question 26

Prerenal azotemia Causative factors include

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

Decreased renal function

Question 29

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

Answer 29

Renal

Question 30

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

Answer 30

Postrenal azotemia

Question 31

major causes of decreased plasma urea concentration

Answer 31

low protein intake and severe liver disease

Question 32

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

Answer 32

pregnancy and in infancy

Question 33

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

Answer 33

normally 10:1 to 20:1

Question 34

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

Answer 34

Prerenal conditions

Question 35

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

Answer 35

postrenal conditions

Question 36

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

Answer 36

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

Question 37

Decreased urea Concentration

Answer 37

Low protein intake Severe vomiting and diarrhea Liver disease Pregnancy

Question 38

Increased urea Concentration

Answer 38

Prerenal Renal Postrenal

Question 39

Prerenal

Answer 39

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

Question 40

Renal

Answer 40

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

Question 41

Postrenal

Answer 41

Urinary tract obstruction