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Validation of the phenylalanine/tyrosine ratio determined by tandem mass spectrometry: sensitive newborn screening for phenylketonuria.
[classical phenylketonuria]
The
efficacy
of
the
tandem
mass
spectrometry
as
a
tool
for
the
newborn
screening
of
phenylketonuria
,
an
inherited
metabolic
disorder
,
was
investigated
.
Precision
,
reproducibility
,
selectivity
and
sensitivity
were
validated
for
phenylalanine
and
tyrosine
measurements
from
dried
blood
spots
.
Bland-
Altman
plots
were
used
to
assess
the
agreement
with
conventional
methods
like
fluorometry
and
ion
exchange
chromatography
.
The
utility
of
the
phenylalanine
/
tyrosine
ratio
for
discrimination
between
mild
hyperphenylalaninemia
and
classical
types
of
phenylketonuria
was
investigated
.
Depending
on
concentration
levels
of
phenylalanine
and
tyrosine
the
within-run
and
between-run
assay
variability
ranged
between
4
.
2
%
and
12
.
7
%
.
Higher
recoveries
and
a
lower
detection
limit
were
found
for
the
mass
spectrometric
method
when
compared
to
the
fluorometric
method
.
Pearson
correlation
coefficients
of
0
.
91
for
tandem
mass
spectrometry
vs
.
fluorometric
method
,
as
well
as
0
.
95
for
tandem
mass
spectrometry
vs
.
ion
exchange
chromatography
were
calculated
.
The
closest
agreement
between
methods
was
observed
between
tandem
mass
spectrometry
and
ion
exchange
chromatography
.
The
results
demonstrate
a
high
efficacy
of
the
tandem
mass
spectrometric
method
for
quantitative
determination
of
phenylalanine
and
tyrosine
from
dried
blood
spots
.
The
phenylalanine
/
tyrosine
ratio
is
crucial
to
improve
the
specificity
and
positive
predictive
value
for
the
diagnosis
of
classical
phenylketonuria
.
