AMMONIA

Question 1

produced in the deamination of amino acids during protein metabolism. It is removed from the circulation and converted to urea in the liver.

Answer 1

Ammonia

Question 2

however, ammonia is present in the plasma in low concentrations

Answer 2

Free ammonia is toxic

Question 3

-produced in the catabolism of amino acids and by bacterial metabolism in the lumen of the intestine
-excreted as ammonium ion by the kidney and acts to buffer urine.

Answer 3

Ammonia (NH3)

Question 4

ammonia is consumed by the parenchymal cells of the liver in the___________________________a nontoxic compound that is excreted in the urine.

Answer 4

KrebsHenseleit or urea cycle to produce urea

Question 5

Clinical conditions in which blood ammonia concentration provides useful information are

Answer 5

hepatic failure, Reye’s syndrome, and inherited deficiencies

Question 6

most common cause of disturbed ammonia metabolism

Answer 6

Severe liver disease

Question 7

The monitoring of blood ammonia may be used to determine prognosis, although correlation between the extent of ______________________________________ is not always consistent.

Answer 7

hepatic encephalopathy and plasma ammonia concentration

Question 8

better indicator of the severity of disease

Answer 8

Arterial ammonia concentration

Question 9

-occurring most commonly in children, is a serious disease that can be fatal. Frequently, the disease is preceded by a viral infection and the administration of aspirin.
-an acute metabolic disorder of the liver, and autopsy findings show severe fatty infiltration of that organ.

Answer 9

Reye’s syndrome

Question 10

can be correlated with both the severity of the disease and prognosis.

Answer 10

Blood ammonia concentration

Question 11

Ammonia is of use in the diagnosis of inherited deficiency of urea cycle enzymes. Testing should be considered for any neonate with unexplained

Answer 11

nausea,
vomiting, or
neurological deterioration associated with feeding

Question 12

can be used to monitor hyperalimentation therapy and measurement of urine ammonia can be used to confirm the ability of the kidneys to produce ammonia

Answer 12

Assay of blood ammonia

Question 13

The accurate laboratory measurement of ammonia in plasma is complicated by its

Answer 13

low concentration, instability, and pervasive contamination

Question 14

which ammonia is isolated from the sample and then assayed.

Answer 14

two-step approach

Question 15

involves direct measurement of ammonia by an enzymatic method or ion-selective electrode

Answer 15

second approach

Question 16

-One of the first analytic methods for ammonia, developed by
-exploited the volatility of ammonia to separate the compound in a microdiffusion chamber

Answer 16

Conway in 1935

Question 17

The amount of ammonia is determined by

Answer 17

titration

Question 18

-Ammonia can be measured by an enzymatic method using
-this method is convenient and the most common technique used currently

Answer 18

GLDH

Question 19

-preferred coenzyme because it is used specifically by GLDH

Answer 19

NADPH

Question 20

NADH will participate in reactions of other endogenous substrates, such as

Answer 20

pyruvate

Question 21

added to the reaction mixture to increase the rate of the reaction and to stabilize GLDH. This method is used on many automated systems and is available as a prepared kit from numerous manufacturers.

Answer 21

Adenosine diphosphate

Question 22

-uses a thin-film colorimetric assay
-In this method, ammonia reacts with an indicator to produce a colored compound that is detected spectrophotometrically

Answer 22

dry slide automated system

Question 23

The electrode measures the change in pH of a
solution of___________as ammonia diffuses across a semipermeable membrane

Answer 23

ammonium chloride

Question 24

extremely important for plasma ammonia assays

Answer 24

Careful specimen handling

Question 25

increases rapidly following specimen collection because of in vitro amino acid deamination

Answer 25

Whole blood ammonia concentration

Question 26

should be obtained without trauma and placed on ice immediately

Answer 26

Venous blood

Question 27

are suitable anticoagulants

Answer 27

Heparin and EDTA

Question 28

should be evaluated for ammonia interference before a new lot is put into use

Answer 28

Commercial collection containers

Question 29

Samples should be centrifuged at ____°C within 20 minutes of collection and the plasma removed

Answer 29

0-4

Question 30

Specimens should be assayed as soon as possible or frozen. Frozen plasma is stable for several days at ___°C

Answer 30

-20

Question 31

contain two to three times as much ammonia as plasma; hemolysis should be avoided

Answer 31

Erythrocytes

Question 32

significant source of ammonia contamination. It is recommended that patients do not smoke for several hours before a specimen is collected

Answer 32

Cigarette smoking by the patient

Question 33

Many substances influence the in vivo ammonia concentration. -may increase ammonia in plasma

Answer 33

Ammonium salts, asparaginase, barbiturates, diuretics, ethanol, hyperalimentation, narcotic analgesics, and some other drugs

Question 34

several antibiotics decrease concentrations

Answer 34

Diphenhydramine, Lactobacillus acidophilus, lactulose, levodopa

Question 35

interferes in dry slide methods

Answer 35

Glucose at concentrations greater than 600 mg/dL (33 mmol/L)

Question 36

potential problem in the laboratory measurement of ammonia

Answer 36

Ammonia contamination

Question 37

must be taken to minimize contamination in the laboratory in which the assay is performed

Answer 37

Precautions

Question 38

Elimination of sources of ammonia contamination can significantly improve the accuracy of ammonia assay results. Sources of contamination include

Answer 38

tobacco smoke, urine, and ammonia in detergents, glassware, reagents, and water

Question 39

ammonia content of serum-based control material is

Answer 39

unstable

Question 40

Frozen aliquots of human serum albumin containing known amounts of________________________ Solutions containing known amounts of ammonium sulfate are commercially available.

Answer 40

ammonium chloride or ammonium sulfate

Question 41

Values obtained vary somewhat with the method used.8 Higher concentrations are seen in

Answer 41

newborns

Question 42

in which there is significant collateral circulation (as in cirrhosis) or if parenchymal liver cell function is severely impaired, ammonia is not removed from the circulation and blood concentration increases.

Answer 42

severe liver disease

Question 43

High concentrations of NH3 are

Answer 43

neurotoxic and often associated with encephalopathy

Question 44

Ammonia alters metabolic processes in the brain, which results in accumulation of

Answer 44

toxic species, and impairs astrocyte function

Question 45

associated with inherited deficiency of urea cycle enzymes. Measurement of plasma ammonia is important in the diagnosis and monitoring of these inherited metabolic disorders

Answer 45

Hyperammonemia