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HelpTest Code A1ALC Alpha-1-Antitrypsin Proteotype S/Z, LC-MS/MS, Serum
Reporting Name
A1AT Proteotype S/Z, LC-MS/MS, SUseful For
Identification of homozygous and heterozygous S and Z proteotypes of alpha-1-antitrypsin deficiency
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| A1ASZ | A1AT Proteotype S/Z, LC-MS/MS | No | Yes |
| AATP | Alpha-1-Antitrypsin, S | Yes, (order AAT) | Yes |
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| A1APR | Alpha-1-Antitrypsin Phenotype, S | Yes, (order A1APP) | No |
Testing Algorithm
If the mass spectrometry proteotype and quantitative serum level are discordant, then phenotyping will be added and performed at an additional charge.
For more information see Alpha-1-Antitrypsin-A Comprehensive Testing Algorithm
Method Name
A1ASZ: Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
AATP: Nephelometry
A1APR: Isoelectric Focusing
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumSpecimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 1.25 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 28 days | |
| Ambient | 28 days | ||
| Frozen | 28 days |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | Reject |
| Gross icterus | OK |
Special Instructions
Reference Values
ALPHA-1-ANTITRYPSIN:
100-190 mg/dL
ALPHA-1-ANTITRYPSIN PROTEOTYPE:
Negative for S and Z phenotype (Non S Non Z)
Day(s) Performed
Monday, Thursday
CPT Code Information
82103
82542
82104 (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| A1ALC | A1AT Proteotype S/Z, LC-MS/MS, S | 102082-5 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| AATP | Alpha-1-Antitrypsin, S | 6771-0 |
| 34855 | A1AT Proteotype S/Z, LC-MS/MS | 49244-7 |
Clinical Information
Alpha-1-antitrypsin (A1A) is a protein that inhibits the enzyme neutrophil elastase. It is predominantly synthesized in the liver and secreted into the bloodstream. The inhibition function is especially important in the lungs because it protects against excess tissue degradation. Tissue degradation due to A1A deficiency is associated with an increased risk for early onset panlobular emphysema, which initially affects the lung bases (as opposed to smoking-related emphysema, which presents with upper-lung field emphysema). Patients may become symptomatic in their 30s and 40s. The most frequent symptoms reported in a National Institute of Health study of 1129 patients with severe deficiency (mean age 46 years) included cough (42%), wheezing (65%), and dyspnea with exertion (84%). Many patients were misdiagnosed as having asthma. It is estimated that approximately one-sixth of all lung transplants are for A1A deficiency. Liver disease can also occur, particularly in children; it occurs much less commonly than emphysema in adults.
Alpha-1-antitrypsin deficiency is a relatively common disorder in those of Northern European ancestry. The diagnosis of A1A deficiency is initially made by quantitation of protein levels in serum followed by determination of specific allelic variants by isoelectric focusing (IEF). While there are many different alleles in this gene, only 3 are common. The 3 major alleles include: M (full functioning, normal allele), S (associated with reduced levels of protein), and Z (disease-causing variant associated with liver disease and premature emphysema). The S and Z alleles account for the majority of the abnormal alleles detected in affected patients. As a codominant disorder, both alleles are expressed. An individual of SZ or S-null genotype may have a small increased risk for emphysema (but not liver disease) due to slightly reduced protein levels. On the other hand, an individual with the ZZ genotype is at greater risk for early onset liver disease and premature emphysema. Smoking appears to hasten development of emphysema by 10 to 15 years. These individuals should be monitored closely for lung and liver function.
Historically, IEF has been the primary method for characterizing variants, although in some cases, the interpretation is difficult and prone to error. Serum quantitation is helpful in establishing a diagnosis but can be influenced by other factors. A proteomic method using trypsin-digested sera can detect the mutated peptides of the S and Z alleles but can miss disease alleles other than the S and Z alleles. This test combines all of these methods to provide a comprehensive result.
Interpretation
For each of the possible alpha-1-antitrypsin (A1A) genotypes there is an expected range for the total serum level of A1A. However, a number of factors can influence either the A1A serum level or the A1A proteotype results, including acute illness (A1A is an acute-phase reactant), protein replacement therapy, the presence of other rare variants, or the presence of rare DNA alterations (ie, polymorphisms). When the serum level differs from what is expected for that proteotype (ie, discordant), additional studies are performed to ensure the most appropriate interpretation of test results. Additional follow-up may include A1A phenotyping by isoelectric focusing, obtaining additional clinical information, and DNA sequencing. See Alpha-1-Antitrypsin Testing Result Table.
Cautions
This assay will not detect 5% of the known genetic variants that cause alpha-1-antitrypsin (A1A) deficiency. Therefore, the absence of a detectable genetic variant does not rule out the possibility that an individual is a carrier of, or affected with, this disease.
Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in the interpretation of results may occur if information given is inaccurate or incomplete.
Rare variants exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.
Errors in interpretation may occur if patients have had a recent blood transfusion or are on A1AÂ replacement therapy.
Method Description
Alpha-1-Antitrypsin Proteotype S/Z
The method detects the differences in mass to charge ratios of alpha-1-antitrypsin (A1A) tryptic peptides containing the S and Z point mutations. Serum from a patient suspected of having an A1A S or Z mutation is prepared for digestion and then digested using trypsin to generate tryptic peptides from the proteins. The peptides are then subjected to liquid chromatography tandem mass spectrometry to interrogate the mixture for peptides consistent with wild type (Non S, Non Z) or mutated (S, Z) peptides from the S and Z A1A phenotypes. Reverse phase liquid chromatography is used to separate the peptides based on hydrophobicity while the eluate is scanned for the desired peptides using a triple quadrupole mass spectrometer operating under Standard Reaction Monitoring principles. Labeled internal standards, which have identical chemistry to the desired peptides but have slightly different masses, are used to assure the detected peptides from the sample are consistent with the internal standard elution times. By detecting the presence or absence of these peptides, the phenotype status for the S and Z alleles can be determined. It should be kept in mind that this method does not detect other phenotypes. Discrepancies between A1A quantitation levels and the results of this test need be followed up with isoelectric focusing testing.(Unpublished Mayo Method)
Alpha-1-Anitrypsin
In this Siemens Nephelometer II method, the light scattered onto the antigen-antibody complexes is measured. The intensity of the measured scattered light is proportional to the amount of antigen-antibody complexes in the sample under certain conditions. If the antibody volume is kept constant, the signal behaves proportionally to the antigen volume.
A reference curve is generated by a standard with a known antigen content on which the scattered light signals of the samples can be evaluated and calculated as an antigen concentration. Antigen-antibody complexes are formed when a sample containing antigen and the corresponding antiserum are put into a cuvette. A light beam is generated with a light emitting diode, which is transmitted through the cuvette. The light is scattered onto the immuno-complexes that are present. Antigen and antibody are mixed in the initial measurement, but no complex is formed yet. An antigen-antibody complex is formed in the final measurement.
The result is calculated by subtracting value of the final measurement from the initial measurement. The distribution of intensity of the scattered light depends on the ratio of the particle size of the antigen-antibody complexes to the radiated wavelength.(Instruction manual: Siemens Nephelometer II. Siemens, Inc; Version 2.3, 2008; Addendum to the Instruction Manual 2.3, 08/2017)