alpha1-Antitrypsin and alpha1-Antitrypsin Phenotyping(redirected from Pi phenotype)
α1-Antitrypsin and α1-Antitrypsin Phenotyping
Synonym/acronym: α1-antitrypsin: A1AT, α1-AT, AAT; α1-antitrypsin phenotyping: A1AT phenotype, α1-AT phenotype, AAT phenotype, Pi phenotype.
To assist in the identification of chronic obstructive pulmonary disease (COPD) and liver disease associated with α1-antitrypsin (α1-AT) deficiency.
SpecimenSerum (1 mL) for α1-AT and serum (2 mL) for α1-AT phenotyping collected in a gold-, red-, or red/gray-top tube. Whole blood from one full lavender-top (EDTA) is also acceptable.
(Method: Rate nephelometry for α1-AT, isoelectric focusing/high-resolution electrophoresis for α1-AT phenotyping)
|Age||Conventional Units||SI Units (Conventional Units × 0.01)|
|0–1 mo||124–348 mg/dL||1.24–3.48 g/L|
|2–6 mo||111–297 mg/dL||1.11–2.97 g/L|
|7 mo–2 yr||95–251 mg/dL||0.95–2.51 g/L|
|3–19 yr||110–279 mg/dL||1.1–2.79 g/L|
|Adult||126–226 mg/dL||1.26–2.26 g/L|
There are three major protease inhibitor phenotypes:
- SS—Intermediate; heterozygous
- ZZ—Markedly abnormal; homozygous
The total level of measurable α1-AT varies with genotype. The effects of α1-AT deficiency depend on the patient’s personal habits but are most severe in patients who smoke tobacco.
α 1-AT is the main glycoprotein produced by the liver. Its inhibitory function is directed against proteolytic enzymes, such as trypsin, elastin, and plasmin, released by alveolar macrophages and bacteria. In the absence of α1-AT, functional tissue is destroyed by proteolytic enzymes and replaced with excessive connective tissue. Emphysema develops at an earlier age in α1-AT–deficient emphysema patients than in other emphysema patients. α1-AT deficiency is passed on as an autosomal recessive trait. Inherited deficiencies are associated early in life with development of lung and liver disorders. In the pediatric population, the ZZ phenotype usually presents as liver disease, cholestasis, and cirrhosis. Greater than 80% of ZZ-deficient individuals ultimately develop chronic lung or liver disease. It is important to identify inherited deficiencies early in life. Typically, α1-AT–deficient patients have circulating levels less than 50 mg/dL. Patients who have α1-AT values less than 140 mg/dL should be phenotyped. Elevated levels are found in normal individuals when an inflammatory process, such as rheumatoid arthritis, bacterial infection, neoplasm, or vasculitis, is present. Decreased levels are found in affected patients with COPD and in children with cirrhosis of the liver. Deficiency of this enzyme is the most common cause of liver disease in the pediatric population. Decreased α1-AT levels also may be elevated into the normal range in heterozygous α1-AT–deficient patients during concurrent infection, pregnancy, estrogen therapy, steroid therapy, cancer, and postoperative periods. Homozygous α1-AT–deficient patients do not show such an elevation.
This procedure is contraindicated for
- Assist in establishing a diagnosis of COPD
- Assist in establishing a diagnosis of liver disease
- Detect hereditary absence or deficiency of α1-AT
- Acute and chronic inflammatory conditions (related to rapid, nonspecific response to inflammation)
- Carcinomas (related to rapid, nonspecific response to inflammation)
- Estrogen therapy
- Postoperative recovery (related to rapid, nonspecific response to inflammation or stress)
- Pregnancy (related to rapid, nonspecific response to stress)
- Steroid therapy
- Stress (extreme physical) (related to rapid, nonspecific response to stress)
- COPD (related to malnutrition and evidenced by decreased protein synthesis) Homozygous α1-AT–deficient patients (related to decreased protein synthesis) Liver disease (severe) (related to decreased protein synthesis) Liver cirrhosis (infant or child) (related to decreased protein synthesis) Malnutrition (related to insufficient protein intake) Nephrotic syndrome (related to increased protein loss from diminished renal function)
- Drugs that may increase total LDH levels include amiodarone, etretinate, Fluosol-DA, methotrexate, oxacillin, plicamycin, propoxyphene, and streptokinase.
- Drugs that may decrease total LDH levels include ascorbic acid, cefotaxime, enalapril, fluorides, naltrexone, and oxylate.
- Hemolysis will cause significant false elevations in total LDH and a false “flip” pattern of the isoenzymes because LDH1 fraction is of red blood cell origin.
- Some isoenzymes are temperature sensitive; therefore, prolonged storage at refrigerated temperatures may cause false decreases.
- α1-AT is an acute-phase reactant protein, and any inflammatory process elevates levels. If a serum C–reactive protein is performed simultaneously and is positive, the patient should be retested for α1-AT in 10 to 14 days.
- Rheumatoid factor causes false-positive elevations.
- Drugs that may increase serum α1-AT levels include aminocaproic acid, estrogen therapy, oral contraceptives (high-dose preparations), oxymetholone, streptokinase, tamoxifen, and typhoid vaccine.
Nursing Implications and Procedure
- 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 identifying lung and liver disease.
- 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 hepatobiliary and respiratory systems, 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). Oral contraceptives should be withheld 24 hr before the specimen is collected, although this restriction should first be confirmed with the health-care provider (HCP) ordering the test.
- Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain to the patient 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.
- 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.
- Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
- Instruct the patient to resume usual medication as directed by the HCP.
- Nutritional Considerations: Malnutrition is commonly seen in α1-AT–deficient patients with severe respiratory disease for many reasons, including fatigue, lack of appetite, and gastrointestinal distress. Research has estimated that the daily caloric intake required for respiration in patients with COPD is 10 times higher than that required in normal individuals. Inadequate nutrition can result in hypophosphatemia, especially in the respirator-dependent patient. During periods of starvation, phosphorus leaves the intracellular space and moves outside the tissue, resulting in dangerously decreased phosphorus levels. Adequate intake of vitamins A and C is important to prevent pulmonary infection and to decrease the extent of lung tissue damage. The importance of following the prescribed diet should be stressed to the patient and caregiver.
- Nutritional Considerations: Water balance must be closely monitored in α1-AT–deficient patients with COPD. Fluid retention can lead to pulmonary edema.
- Educate the patient with abnormal findings in preventive measures for protection of the lungs (e.g., avoid contact with persons who have respiratory or other infections; avoid the use of tobacco; avoid areas having highly polluted air; and avoid work environments with hazards such as fumes, dust, and other respiratory pollutants).
- Instruct the affected patient in deep breathing and pursed-lip breathing to enhance breathing patterns as appropriate. Inform the patient of smoking cessation programs, as appropriate.
- Recognize anxiety related to test results, and be supportive of fear of shortened life expectancy. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Because decreased α1-AT can be an inherited disorder, it may be appropriate to recommend resources for genetic counseling if levels less than 140 mg/dL are reported. It may also be appropriate to inform the patient that α1-AT phenotype testing can be performed on family members to determine the homozygous or heterozygous nature of the deficiency.
- Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Inform the patient of the importance of medical follow-up, and suggest ongoing support resources to assist the patient in coping with chronic illness and possible early death. 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 tests include ACE, anion gap, arterial/alveolar oxygen ratio, biopsy lung, blood gases, blood pool imaging, bronchoscopy, electrolytes, lung perfusion scan, lung ventilation scan, osmolality, PET heart, phosphorus, PFTs, plethysmography, and pulse oximetry if COPD is suspected. ALT, albumin, ALP, ammonia, bilirubin and fractions, biopsy liver, cholangiography percutaneous transhepatic, cholangiography post-op, CT biliary tract and liver, ERCP, GGT, hepatobiliary scan, liver and spleen scan, protein and fractions, PT/INR, and US liver if liver disease is suspected.
- See the Hepatobiliary and Respiratory systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners