38 |
Klinisk Biokemi i Norden · 3 2013
Diagnostic efficiency of European specialist
porphyria laboratories
Study III was based on five distributions of a case-
based external quality assessment (EQA) scheme
including 18 - 21 European specialist porphyria labora-
tories (13). In every distribution, participants received
native urine, faeces and blood samples from a patient
with an equivocal porphyria diagnosis, accompanied
by a clinical case history. Reporting included pre-ana-
lytical (diagnostic strategies based on the clinical case
history), analytical (results for all available porphyria-
related biochemical laboratory analyses with informa-
tion on methodology, units and reference limits) and
post-analytical (diagnosis, reporting and laboratory
report forms) aspects.
Our results showed that the specialist laboratories
applied diverse diagnostic strategies for the diagnosis
of the porphyrias (Table 2). Large variations in ana-
lytical performance were evident in all distributions,
also when reported results were normalised by the
upper reference limits (Table 2). Overall the quality
of the post-analytical phase was high, with most
laboratories providing appropriate interpretations of
laboratory test results and correct diagnoses. Though
it is generally assumed that EQA scheme participa-
tion improves performance in clinical laboratories,
few published studies are available to document this.
In our study, improvements in the applied diagnostic
strategies, a more standardised use of units and sample
collection were observed. Presently about 35 specialist
porphyria laboratories worldwide participate in this
EQA scheme (14).
Conclusions and future perspectives
Quality of care for patients with porphyria diseases is
affected by the fact that they are rare diseases with a
heterogeneous clinical and biochemical expression. In
order to improve the quality of the diagnoses in the
laboratory, participation in a case-based EQA scheme
assessing all aspects of the diagnostic process may
prove useful. Furthermore, methods for biochemical
porphyria-related analyses must be harmonised and
evidence-based diagnostic criteria and data on their
performance established for all the diseases. In order
to obtain large enough patient numbers to produce
high-quality research, data from across countries must
be pooled. The European Porphyria Network (15) has
recently launched the European Porphyria Registry
(EPR), located at the Norwegian Porphyria Centre in
Bergen. The EPR will in future provide an important
tool to increase our understanding and thus the quality
of care for these potentially chronically debilitating and
life-threatening diseases.
Table 2.
In two distributions (A and E), samples were from a patient with acute intermittent porphyria. Three first-line analyses
are necessary for adequate diagnostics in such cases, and “n” indicates the fraction of laboratories that selected these first-line ana-
lyses in light of the accompanying clinical case histories. Analytical results are shown for all EQA scheme participants as means,
interlaboratory CVs and results normalised by the upper reference limits (NR).
A
E
n
Mean CV
(%)
NR
(median
10
th
, 90
th
)
n
Mean CV
(%)
NR
(median
10
th
, 90
th
)
Urinary PBG
18/18 53.7
a
31.0
46.5
(20.1, 65.3)
21/21 6.1
a
64.4
4.1
(0.4, 11.4)
Faecal fractions;
coproporphyrin isomer III:I ratio
7/18
0.5
26.2
17/21
0.6
32.6
Plasma fluorescence
scanning
14/18 14/16
b
19/21 2/20
b
a
In μmol/mmol creatinine.
b
Number of laboratories reporting a positive result out of the total number reporting.
