The importance of early detection and
screening
Because AATD is still largely underdiagnosed (<10%
of what would be expected from epidemiological
data), early detection of AATD subjects remains a
primary concern and must be conducted in reference
centres that can provide the best diagnostic tools.
The laboratory diagnosis of AATD has evolved
over the past 50 years, since the first cases of the
disorder were reported. The diagnostic procedure
is complex because it comprises both quantitative
and qualitative tests. The use of dried blood spots
(drops of blood that have been dried onto a special
filter paper) for the routine laboratory diagnosis of
AATD has become widespread and has facilitated
centralisation of testing. 22–24 This kind of matrix
allows easier preservation and shipping of samples,
thereby allowing wide detection or screening
programs for AATD. 11
Determination of AAT plasma level is the first
crucial analysis, usually performed by nephelometry.
Systemic inflammatory status parallels increased
levels of AAT and this increase might mask the
presence of AATD variants; 25 for this reason, many
reference centres perform the simultaneous
determination of C-reactive protein and AAT in
order to avoid the misdiagnosis of heterozygote-
subjects carrying intermediate AATD genotypes. 26
Most laboratories and screening programs
perform genotyping for the two most common
disease-associated alleles, S and Z; usually
the presence or absence of S and Z variants is
established using genotype-based, allele-specific
amplification by quantitative polymerase chain
reaction. Reflex testing for the identification of
other variants is usually performed using isoelectric
focusing (IEF). The principle of IEF is the separation
of proteins based on their charge in a pH gradient
fixed in the gel. AAT phenotypes are classified by
a coding system in which the inherited alleles are
usually letters that denote the migration of the
molecule in an isoelectric pH gradient from A (for
anodal variants) to Z (for slower migrating variants).
Many AAT genetic variants reflect point mutations
in the gene sequence leading to amino acid
substitutions, which may affect the electrophoretic
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however, existing guidelines recommend testing of
all COPD patients, irrespective of age and severity.
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features as non-deficient COPD, including increased
evidence of bronchiectasis, chronic bronchitis,
bacterial colonisation, frequent exacerbations,
impaired health status and a degree of reversibility
of airflow obstruction. Therefore, the World Health
Organization guidance for testing every patient with
a diagnosis of COPD or adult-onset asthma for AATD
should be standard. 29 This recommendation has been
strengthened by the European Respiratory Society
Statement. 27
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