G6PD

Glucose-6-Phosphate Dehydrogenase

Synonym/acronym: G6PD.

Common use

To identify an enzyme deficiency that can result in hemolytic anemia.

Specimen

Whole blood (1 mL) collected in a lavender-top (EDTA) tube.

Normal findings

(Method: Fluorescent) Qualitative assay—enzyme activity detected; quantitative assay—the following table reflects enzyme activity in units per gram of hemoglobin:

Age	Conventional Units	SI Units (Conventional Units × 0.0645)
Newborn	7.8–14.4 international units/g hemoglobin	0.5–0.93 micro units/mol hemoglobin
Adult–older adult	5.5–9.3 international units/g hemoglobin	0.35–0.60 micro units/mol hemoglobin

Description

Glucose-6-phosphate dehydrogenase (G6PD) is a red blood cell (RBC) enzyme. It is involved in the hexose monophosphate shunt, and its function is to protect hemoglobin from oxidation. G6PD deficiency is an inherited X-linked abnormality; approximately 20% of female carriers are heterozygous. This deficiency results in hemolysis of varying degrees and acuity depending on the severity of the abnormality. There are three G6PD variants of high frequency in different ethnic groups. G6PD A–is more common in African Americans (10% of males) than in other populations. G6PD Mediterranean is especially common in Iraqis, Kurds, Sephardic Jews, and Lebanese and less common in Greeks, Italians, Turks, North Africans, Spaniards, Portuguese, and Ashkenazi Jews. G6PD Mahidol is common in Southeast Asians (22% of males). Polymerase chain reaction (PCR) methods that can detect gene mutations for the enzyme in whole blood are also available. Counseling and written, informed consent are recommended and sometimes required before genetic testing.

This procedure is contraindicated for

N/A

Indications

Assist in identifying the cause of hemolytic anemia resulting from drug sensitivity, metabolic disorder, or infection
Assist in identifying the cause of hemolytic anemia resulting from enzyme deficiency

Potential diagnosis

Increased in

The pathophysiology is not well understood but release of the enzymes from hemolyzed cells increases blood levels.
Chronic blood loss (related to reticulocytosis; replacement of RBCs)
Hepatic coma (pathophysiology is unclear)
Hyperthyroidism (possible response to increased basal metabolic rate and role of G6PD in glucose metabolism)
Idiopathic thrombocytopenic purpura
Megaloblastic anemia (related to reticulocytosis; replacement of RBCs)
Myocardial infarction (medications [e.g., salicylates] may aggravate or stimulate a hemolytic crisis in G6PD-deficient patients)
Pernicious anemia (related to reticulocytosis; replacement of RBCs)
Viral hepatitis (pathophysiology is unclear)

Decreased in

Congenital nonspherocytic anemia G6PD deficiency Nonimmunological hemolytic disease of the newborn

Critical findings

N/A

Interfering factors

Drugs that may increase G6PD levels include fluorouracil.
Drugs that may precipitate hemolysis in G6PD deficient individuals include acetanilid, acetylsalicylic acid, ascorbic acid, chloramphenicol (Chloromycetin), dapsone, doxorubicin, furazolidone, isobutyl nitrate, methylene blue, nalidixic acid, naphthalene, niridazole, nitrofurantoin, para-aminosalicylic acid, pentaquine, phenacetin, phenazopyridine, phenylhydrazine, primaquine, quinidine, quinine, sulfacetamide, sulfamethoxazole, sulfanilamide, sulfapyridine, sulfisoxazole, thiazolsulfone, toluidine blue, trinitrotoluene, urate oxidase, and vitamin K.
G6PD levels are increased in reticulocytes; the test results may be falsely positive when a patient is in a period of acute hemolysis. G6PD levels can also be affected by the presence of large numbers of platelets and white blood cells, which also contain significant amounts of the enzyme.

Nursing Implications and Procedure

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this test can assist in diagnosing anemia.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
Obtain a history of the patient’s hematopoietic system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

Potential complications: N/A
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
Nutritional Considerations: Educate the patient with G6PD deficiency, as appropriate, to avoid certain foods, vitamins, and drugs that may precipitate an acute episode of intravascular hemolysis, including fava beans, ascorbic acid (large doses), acetanilid, antimalarials, furazolidone, isobutyl nitrate, methylene blue, nalidixic acid, naphthalene, niridazole, nitrofurantoin, phenazopyridine, phenylhydrazine, primaquine, sulfacetamide, sulfamethoxazole, sulfanilamide, sulfapyridine, thiazolsulfone, toluidine blue, trinitrotoluene, and urate oxidase.
Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include biopsy bone marrow, bilirubin, CBC, CBC RBC morphology (including examination of peripheral smear for the presence of Heinz bodies), direct antiglobulin test, folate, Ham’s test, haptoglobin, hemosiderin, newborn screening, osmotic fragility, reticulocyte count, UA, and vitamin B₁₂.
Refer to the Hematopoietic System table at the end of the book for related tests by body system.