Zusammenfassung:
Eine moderate Hyperhomocysteinämie (>12 µmol/l) ist der D.A.CH.-Liga Homocystein zufolge bei 5-10% der Allgemeinbevölkerung und bei bis zu 40% der Patienten mit Gefäßerkrankungen zu erwarten, weshalb die Bestimmung des Homocysteins ein Teil des individuellen Risikoprofils für Patienten mit Herz-Kreislauf-Erkrankungen sein sollte.
In der vorliegenden Arbeit wurde der Immulite 2500 Homocystein-Assay der Firma DPC (Diagnostic Products Corporation) Biermann analytisch evaluiert.
Bei dem Immulite 2500 Homocystein-Assay handelt es sich um einen kompetitiven Festphasen-Chemilumineszenz-Immunoassay. Für die Messung der Intra-Assay-Präzision (n=20) wurden Patientenseren vier unterschiedlicher Konzentrationen und Kontrollen drei verschiedener Level gemessen. Die Inter-Assay-Präzision (n=12) wurde ebenfalls mit den drei Kontrollen und mit Patientenseren in drei verschiedenen Konzentrationen durchgeführt. Desweiteren wurden die Verschleppung und die Verdünnungslinearität gemessen. Zur Ermittlung der Stabilität des Homocysteins in verschiedenen Blutentnahmeröhrchen wurde die Homocysteinkonzentration über 24 Stunden gemessen. Ein Methodenvergleich wurde mit dem ADVIA Centaur (Bayer) und der Hochdruckflüssigkeitschromatographie (HPLC) anhand von 118 Patientenproben und zusätzlich anhand von 110 Dialysepatientenproben durchgeführt und nach Bablock/Passing und Bland/Altman ausgewertet.
Die Messung der Intra-Assay-Präzision ergab Variationskoeffizienten in einem Bereich von 3,9% bis 7,4%. Die Variationskoeffizienten der Inter-Assay-Präzision lagen zwischen 5,2% und 10,4%. Die Linearität wurde in einem Bereich von 2,7 µmol/l bis 45,5 µmol/l getestet, wobei die lineare Regression im ersten Ansatz bei R = 0,9941 und im zweiten Ansatz bei R = 0,996 lag.
Bei Messungen einer hohen Probe (Mittelwert 46,4 µmol/l) und einer niedrigen Probe (Mittelwert 6,2 µmol/l) im Wechsel wurde keine Verschleppung der hohen Probe in die niedrige Probe festgestellt.
Der Methodenvergleich mit dem ADVIA Centaur der Firma Bayer und der HPLC wurde mit Proben in einem Bereich von 2,8 µmol/l bis 38,2 µmol/l bzw. mit Proben von Dialysepatienten in einem Bereich von 2,9 µmol/l bis 49,8 µmol/l durchgeführt. Hier ergaben sich gute Korrelationskoeffizienten von R=0,992 für den Vergleich des Immulite 2500 mit dem Centaur und R=0,994 für den Vergleich des Immulite 2500 mit der HPLC. Auch in der vergleichenden Messung der Dialysepatientenproben korrelieren die ermittelten Ergebnisse gut (R = 0,971 (ADVIA Centaur) und R = 0,993 (HPLC)). Festgestellt wurde im Methodenvergleich mittels Bland/Altman, dass sowohl der ADVIA Centaur als auch die HPLC identische Patientenproben höher messen als der Immulite 2500. Diese Abweichungen nahmen im Bereich höherer Konzentrationen zu, was einen proportionalen Fehler demonstriert.
Um das Verhalten der Homocysteinkonzentration in unterschiedlichen Blutentnahme-Röhrchen und unter der Voraussetzung zentrifugiert oder nicht zentrifugiert zu untersuchen, wurde eine Stabilitätsmessung über 24 Stunden bei Aufbewahrung der Proben bei Raumtemperatur vorgenommen. Verwendet wurden EDTA-Plasma-, Heparin-Plasma- und Serum-Röhrchen. Die Ergebnisse zeigten einen starken Anstieg der Homocysteinkonzentration in allen nicht zentrifugierten Proben. In den zentrifugierten Proben verhielt sich die Homocysteinkonzentration annähernd konstant.
Der Immulite 2500 Homocystein-Assay ist einfach in der Handhabung und liefert nach 65 Minuten das Ergebnis. Empfohlen ist eine Verwendung von Heparin- oder EDTA-Plasma. Auch Serum kann verwendet werden, sollte aber umgehend zentrifugiert werden. Der Immulite 2500 Homocystein-Assay ist geeignet für den Einsatz im Routinelabor.
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