Alternative name: PI phenotyping
General information α1-Antitrypsin deficiency
Description: There are >59 variants which result in varying levels of a1-antitrypsin and are associated with different symptom levels. Phenotypes are designated as Pi phenotypes – M, S, Z, F etc. PIMM (i.e homozygous) have 40% reduction in levels, PiMZ (heterozygous) 85% reduction. One rare type Mduarte produces a normal concentration of functionally deficient protein.The test should be performed in adults if α1-antitrypsin levels are determined to be below age related median result. Phenotyping should be determined in all children with liver disease irrespective of AAT concentration. Severe genetic deficiencies of α1-antitrypsin (<0.6g/L) occur with an incidence of around 1 in 2,000.
Indication: Investigation of genetic origin of adults/children with α1-antitrypsin deficiency. Investigation of all children with liver disease irrespective of α1-antitrypsin levels. Used in family screening for deficiency when deficient sibling has been identified.
Interpretation: Patients who are homozygous for a deficiency allele or are heterzygous for two deficiency alleles will have a severe reduction of serum a1 antitrypsin (<0.6g/L). A hetererozygous state with one deficiency allele and one “normal” allele will normally have level 0.6-1.4 g/L. The laboratory will use as a lower limit of normal of 1.0g/L for carrying out phenotypic analysis.
Sample: Serum Separator Tube (SST)
Assay details: Isoelectric focusing in polyacrylamide gel (pH 4-5).
Restrictions: Referred test
Reference range: Descriptive report
Assay range notes:
Turnaround time: 14 Days
Analysing laboratory: Sheffield Protein Reference Unit