Glucose-6-Phosphate Dehydrogenase

Synonym/Acronym:
G6PD.

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

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
(Method: Enzymatic) 7–15 units/G hemoglobin; SI Units (Conventional Units × 0.0645) = 0.45–0.97 micro units/mol hemoglobin.

Critical Findings and Potential Interventions
N/A

Overview

(Study type: Blood collected in a lavender-top [EDTA] tube; related body system: Circulatory system.) 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 the most common enzyme abnormality and affects over 400 million people worldwide. This deficiency results in hemolysis of varying degrees and acuity depending on the severity of the abnormality. Globin chains from the oxidized hemoglobin attach to the RBC membrane and can be seen in stained peripheral smears; the round inclusions are called Heinz bodies and are associated with hemolytic anemias such as G6PD deficiency. The deficiency is passed on as a sex-linked recessive (X chromosome) mutation expressed more frequently in males than in females. There are numerous G6PD variants, and of these three have a high frequency in specific ethnic groups. G6PD A is more common in males of African descent (10%) 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.

Knowledge of genetics assists in identifying those who may benefit from additional education, risk assessment, and counseling. Genetics is the study and identification of genes, genetic mutations, and inheritance. For example, genetics provides some insight into the likelihood of inheriting a medical condition such as G6PD deficiency. Some conditions are the result of mutations involving a single gene, whereas other conditions may involve multiple genes and/or multiple chromosomes. G6PD is an example of a recessive sex-linked genetic disorder passed from a mother to male children. Further information regarding inheritance of genes can be found in the study titled "Genetic Testing."

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

Interfering Factors

Factors that may alter the results of the study

  • Drugs and other substances that may increase G6PD levels include fluorouracil.
  • Drugs and other substances that may precipitate hemolysis in G6PD-deficient individuals include acetylsalicylic acid, ascorbic acid (large doses), chloramphenicol, dapsone, doxorubicin, furazolidone, methylene blue, nalidixic acid, naphthalene, niridazole, nitrofurantoin, pentaquine, phenazopyridine, phenylhydrazine, primaquine, quinidine, quinine, sulfacetamide, sulfamethoxazole, sulfanilamide, sulfapyridine, sulfisoxazole, thiazolsulfone, toluidine blue, uricase (rasburicase), 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.

Potential Medical Diagnosis: Clinical Significance of Results

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

Nursing Implications

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

  • Inform the patient this test can assist in diagnosing anemia.
  • Explain that a blood sample is needed for the test.

After the Study: Potential Nursing Actions

Treatment Considerations

  • Chronic fatigue related to anemia can be problematic for the patient in maintaining activities of daily living. Collaborate with the patient to prioritize activities and conserve energy. Discuss limiting daytime napping to facilitate nighttime sleeping. Correct anemia with ordered interventions such as blood transfusion.

Nutritional Considerations

  • Educate the patient with G6PD deficiency, as appropriate, to avoid certain foods (e.g., fava beans), vitamins, and drugs that may precipitate an acute episode of intravascular hemolysis.

Followup Evaluation and Desired Outcomes

  • Acknowledges key signs and symptoms of hemolytic anemia that must be reported to the health-care provider to include back pain, fatigue, jaundice, rapid breathing, and rapid heart rate; knowledge of signs and symptoms is especially important for individuals in high-risk groups based on age (newborns with severe jaundice that does not resolve), ethnicity (African, Middle Eastern, or Asian descent with a family history of hemolytic anemia), and gender (males with a family history of jaundice, enlarged spleen or hemolytic anemia).

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