Anticorpi anti-Saccharomyces cerevisiae (ASCA)

La ricerca degli anticorpi anti-Saccharomyces
cerevisiae viene effettuata per la diagnosi differenziale tra il morbo di Crohn e la colite ulcerosa, i due tipi più comuni

di malattia infiammatoria cronica intestinale (MICI). Questo test in genere rileva la presenza nel circolo ematico di due classi di anticorpi, IgG e IgA.

La diagnosi di MICI viene effettuata principalmente da esami non di laboratorio, come l’esame bioptico intestinale. In alcuni casi però, la diagnosi differenziale tra colite ulcerosa e morbo di Crohn con la sola valutazione clinica può essere difficile e quindi richiedere l’esecuzione del test ASCA e pANCA (anticorpi anti-perinucleo
dei neutrofili). La presenza di ASCA è maggiormente comune nel morbo di Crohn mentre i pANCA si rilevano più frequentemente nella colite ulcerosa. Gli
anticorpi anti-CBir1 (anti-flagellina) e anti-Omp C (anti- membrana plasmatica esterna) sono invece indicativi di morbo di Crohn e possono essere richiesti in associazione al test ASCA.

Il test ASCA viene richiesto in persone
con segni e sintomi di MICI per la diagnosi differenziale tra morbo di Crohn e colite ulcerosa. Può essere richiesto insieme ai pANCA e ad altri test anticorpali.
 
I segni e sintomi di MICI possono includere:

• Dolore e crampi addominali Diarrea
• Sanguinamento rettale Febbre
• Senso di fatica
• In alcune persone, sintomi associati alle articolazioni, la pelle, le ossa o gli organi
• Nei bambini, possibile ritardo nello sviluppo e nella crescita

Un risultato positivo per la presenza di ASCA non è diagnostico per morbo di Crohn, colite ulcerosa o altre MICI, ma rende probabile che i sintomi di una persona siano riconducibili alla presenza di MICI.

Il risultato del test ASCA spesso viene interpretato in associazione ad altri esami, come la ricerca dei pANCA:

• ASCA positivo e pANCA negativo – probabile presenza di morbo di Chron
• ASCA negativo e pANCA positivo – probabile presenza di Colite Ulcerosa

Un risultato negativo di ASCA e/o pANCA però non esclude necessariamente la presenza di MICI.

La presenza di più anticorpi (ASCA, anti-CBir1, anti-Omp
C) potrebbe essere associata a patologie più aggressive ma la loro assenza non esclude tale possibilità.

La quantità di ASCA o pANCA presenti non correla con la gravità della malattia e non può essere utilizzata nel monitoraggio della terapia.

In alcuni casi, potrebbe essere richiesto un pannello di esami comprendente, oltre agli ASCA e ai pANCA, anche gli anti-CBir1 (anti-flagellina) e gli anti-Omp C (anti- proteine di membrana), con lo scopo di fare diagnosi differenziale tra le malattie infiammatorie croniche intestinali (MICI) e di avere informazioni di tipo prognostico per il morbo di Crohn. La presenza di più anticorpi indica con buona probabilità una forma più aggressiva, anche se la loro assenza non correla necessariamente con forme meno aggressive.

Poiché i sintomi delle MICI sono spesso sovrapponibili a quelli di altre patologie, potrebbero essere richiesti anche altri esami di approfondimento.

Il test di solito viene effettuato una volta sola, come ausilio alla diagnosi differenziale tra morbo di Chron
e colite ulcerosa. Tipicamente il test viene effettuato per rilevare sia le ASCA IgG che le ASCA IgA contemporaneamente. Tuttavia, nel caso in cui venga

richiesta solo una delle due classi di immunoglobuline, allora il test può essere effettuato nuovamente per rilevare l’altra.

I livelli di questi anticorpi possono variare nel tempo ma una volta prodotti non possono scomparire.

No, l’esecuzione del test richiede personale e strumentazione specializzati presenti nei laboratori e può richiedere qualche giorno.

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