Interpretive Handbook

Test 26953 :
Alpha-1-Antitrypsin Phenotype




Most normal individuals have the M phenotype (M, M1, or M2). Over 99% of M phenotypes are genetically MM. In the absence of family studies, the phenotype (M) and quantitative level can be used to infer the genotype (MM). The most common alleles associated with a quantitative deficiency are Z and S.




Identification of homozygous and heterozygous phenotypes of the alpha-1-antitrypsin deficiency

Interpretation Provides information to assist in interpretation of the test results

There are >40 alpha-1-antitrypsin (A1A) phenotypes (most of these are associated with normal quantitative levels of protein). The most common normal phenotype is M (M, M1, or M2), and >90% of Caucasians are genetically homozygous M (MM).


A1A deficiency is usually associated with the Z phenotype (homozygous ZZ), but SS and SZ are also associated with decreased A1A levels.


This assay identifies the phenotype of the circulating alpha-1-antitrypsin (A1A) protein. If the patient is already on replacement therapy, the phenotype will detect patient and replacement protein.


If 2 bands are seen, such as an M band and a Z bands, it is reported as MZ (eg, heterozygous)


If 1 band is seen, such as the Z band and the quantitative level is consistent with a homozygote, the phenotype is assumed to be homozygous and is reported as ZZ.



100-190 mg/dL



The interpretive report will identify the alleles present. For rare alleles, the report will indicate whether or not they have been associated with reduced quantitative levels of alpha-1-antitrypsin.


1. Morse JO: Alpha-1-antitrypsin deficiency. N Engl J Med 1978;299:1045-1048;1099-1105

2. Donato LJ, Jenkins SM, Smith C, et al: Reference and interpretive ranges for alpha(1)-antitrypsin quantitation by phenotype in adult and pediatric populations. Am J Clin Pathol 2012 Sep;138(3):398-405