AMMONIA

Ammonia

deamination of amino acids during protein metabolism.

Ammonia

removed from the circulation and converted to urea in the liver

Free ammonia

toxic to human cells

Ammonia

present in the plasma in low concentrations.

Some endogenous ammonia

results from anaerobic metabolic reactions that occur in skeletal muscle during exercise.

urea

nontoxic compound

Ammonia

excreted as ammonium ion by the kidney and acts to buffer urine.

Clinical Application

hepatic failure, Reye’s syndrome, and inherited deficiencies of urea cycle enzymes.

Severe liver disease

most common cause of disturbed ammonia metabolism.

Arterial ammonia concentration

better indicator of the severity of disease

Reye’s syndrome

occurring most commonly in children, is a serious disease that can be fatal.

Reye’s syndrome

acute metabolic disorder of the liver, and autopsy findings show severe fatty infiltration of that organ.

Blood ammonia concentration

can be correlated with both the severity of the disease and prognosis; as ammonia levels rise, the prognosis decreases.

Survival reaches 100%

plasma NH3 concentration remains below five times normal.

Ammonia

use in the diagnosis of inherited deficiency of urea cycle enzymes.

Blood ammonia

used to monitor hyperalimentation therapy

urine ammonia

used to confirm the ability of the kidneys to produce ammonia.

low concentration, instability, and pervasive contamination.

accurate laboratory measurement of ammonia in plasma is complicated

two-step approach

ammonia is isolated from the sample and then assayed.

enzymatic method or ion selective electrode

direct measurement of ammonia

microdiffusion chamber

One of the first analytic methods for ammonia

developed by Conway in 1935, exploited the volatility of ammonia to separate the compound in a

GLDH

enzymatic method

This method is convenient and the most common technique used currently.

thin-film colorimetric assay

dry slide automated system

In this method, ammonia reacts with an indicator to produce a colored compound that is detected spectrophotometrically

ion-selective electrode

Direct measurement has been developed.

The electrode measures the change in pH of an ammonium chloride solution as ammonia diffuses across a semipermeable membrane.

Whole blood ammonia concentration

increases rapidly folowing specimen colection because of in vitro amino acid deamination.

Venous blood

should be obtained without trauma and placed on wet ice immediately.

Heparin and EDTA

are suitable anticoagulants.

0 to 4°C within 20 minutes of colection

Samples should be centrifuged at _____ and the plasma removed.Specimens should be assayed as soon as possible or frozen.

assayed, frozen

Specimens should be _____ as soon as possible or _____.

–20°C

Frozen plasma is stable for several days at

Erythrocytes, avoided

contain two to three times as much ammonia as plasma;

hemolysis should be _____

Cigarette smoking

by the patient is a significant source of ammonia contamination.

increase

Ammonium salts, asparaginase, barbiturates, diuretics, ethanol, hyperalimentation, narcotic analgesics, and some other drugs may _____ ammonia in plasma.

decrease

Diphenhydramine, Lactobacillus acidophilus, lactulose, levodopa, and several antibiotics _____ concentrations.

dry slide

Glucose at concentrations greater than 600 mg/dL (33 mmol/L) interferes in _____ methods

Ammonia contamination

potential problem in the laboratory measurement of ammonia

Sources of contamination

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

unstable

ammonia content of serum-based control material is _____

ammonium chloride or ammonium sulfate

Frozen aliquots of human serum albumin containing known amounts of _____ or _____ may be used.

ammonium sulfate

Solutions containing known amounts of _____ are commercially available.

newborns

Higher concentrations are seen in _____.

Hyperammonemia

associated with inherited deficiency of urea cycle enzymes.