Akademik Veri Yönetim Sistemi
TBD-BD Preanalytic Phase Symposium 2018, Kayseri, Türkiye, 28 - 29 Nisan 2018, cilt.43, sa.2, ss.4
PREANALYTIC PHASE IN IMMUNOCHEMISTRY
Didem Barlak Keti Department of Biochemistry, Faculty of Medicine, Erciyes University, Kayseri
In spite of the improvements in laboratory medicine, the pre-analytical phase
is still the main responsible for laboratory errors. Immunoassay is an important
part of the diagnostic process. Because of the relatively low concentrations of
analyte being measured and the complexities of the antigen-antibody interaction,
this technique is relatively susceptible to interferences. There are many possible
reasons for false results to be obtained during an immunoassay procedure.
Interferences in immunoassay fall in to two broad categories: analyte-independent
and analyte-dependent.
Analyte-dependent interferences
○Cross reacting substances (lack of specificity)
○Endogenous antibodies
Antireagent antibodies (heterophile, HAAA, RF)
Antianalyte antibodies-autoantibody (macro complexes)
○Hook effect
Analyte-independent interferences
○ Inadequate centrifugation with microclots
○ Hemolysis, lipemia, icterus
○ Specimen collection tubes, transport, stability and storage
○ Disease states
The ways of becoming aware of possible interferences and the investigation them
Discordant results
Clinical interaction
High index of suspicion
Exclude pre-analytical problems
Repeat analysis on another instrument from a different manufacturer
Treatment with heterophilic blocking reagents
PEG precipitation
Serial dilutions
Check using a different matrix e.g. urine for hCG
Selective removal of immunoglobulins
Chromatography
Tandem-mass spectrometry
Falsely high or falsely low results due to interferences endogenous to the specimen
present a particular risk to patient care because they (a) are not detectable by
normal laboratory quality control procedures, (b) are reproducible within the test
system, (c) are often clinically plausible and (d) are relatively rare.
The mechanism of interference and its severity depend both on assay design
(two-site; one step) and on the nature of the interfering antibody.
It is important to recognize that interfering antibodies may be present only
transiently in a patient’s serum, and that their characteristics and reactivity may
vary, such that no immunoassay can be considered to be completely robust to all
possible interference. Therefore it is important to inform clinicians and activate
the consultation process between the departments.
References
1. Greg Warda, Aaron Simpsonb, Lyn Boscatoc, Peter E. Hickman. The
investigation of interferences in immunoassay. Clin Biochem 2017; 50: 1306- 13
11.
2. Catharine M Sturgeon and Adie Viljoen. Analytical error and interference in
immunoassay: minimizing risk Ann Clin Biochem 2011; 48: 418-432.
3. Ellen Anckaert and Johan Smitz, Interferences in ImmunoassaysJohan
Schiettecatte, Laboratory Clinical Chemistry and Radioimmunology, Belgium
PREANALYTIC PHASE IN ADVANCED SYSTEMS
Fehime Benli Aksungar
Acıbadem University, School of Medicine, Department of Biochemistry
Acıbadem Labmed Clinical Laboratories, Advanced Tests and Metabolism
Section, Istanbul
Diagnostic medical branches such as clinical biochemistry, clinical microbiology,
pathology and radiology, keep pace with technology in a faster way than other
medical areas. In the last 15 years, with the emergence of electrospray ionisation
(ESI) method especially for the ionization of molecules, mass spectrometry
finds place in routine laboratories. All analyse methods have three common
stages: Isolating the particular analyte from a complex matrix, determining
the concentration and reporting the result in proper units. Mass spectrometers
(MS) determine analyte concentrations more accurately than the other systems.
Especially therapeutic drug concentrations, biologic amins and steroid hormon
measurements are more sensitive in MS measurements. Today, in routine
laboratories, small molecule (metabolite) analyzes are shifting towards mass
spectrometers. High-precision measurement of modern MS systems means that
chemical contamination is also measured. Hence, preanalytical errors can lead
to serious errors in these systems. In the clinical laboratories, in addition to the
pre-analtytical phase of routine biochemistry and hormone systems, preanalytical
phase of MS systems must be evaluated and unfortunately the process has to be
re-examined from the very beginning. Sample collecting time, sex, age, fasting
state, sample types, tubes and sample containers should be re-examined for MS
systems. The preferred sample type for blood analysis in MS systems is plasma.
In addition, dried blood spot (DBS) is accepted to be an alternative sample for MS
measurements. Plasma and serum metabolic profiles are different. Metabolism of
the cells in serum continues until coagulation has occurred. In particular, platelets
are active from the moment they are removed out from the body, and secrete
many metabolites during coagulation eg. lipids and proteases. It is important that
the plazma or whole blood can be placed directly in ice.
Preanalytic stage standardization in MS systems:
1. Before validating the method, evaluation should be done for any contamination
from water, equipment used: tubes, pipette tips
2. Hemolytic specimens must be handled carefully and clarify the interaction
with the analyte
3. As soon as samples are collected, precautions must be taken to quickly start
the cooling process
4. Cells from plasma/serum should be separated as quickly as possible and
samples should be transferred to secondary tubes
5. Samples to be stored for analysis should be stored at -20 ° C and then at -80 ° C
6. Repeated thawing-freezing is not acceptable
7. A standardized / validated SOP should be prepared for sample pretreatment
prior to analysis
8. An SOP is also required for each new method, containing sample collection,
separation, transport, storage and sample preparation steps.
Metal analyzes have been performed by Atomic Absorption Spectrometry (AAS)
or Atomic Emission Spectrometry (AES) methods from the early 1900’s. In the
last 20 years, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) has
been developed to measure simultaneous and highly precise measurement of
multiple heavy metals in a single run Whole blood, serum, urine and CSF heavy
metals can be analyzed by these systems. Contamination may be a problem
during sample collection and analysis. Hence special equipment and training are
required for the sample collection