I think they are trying to rule out neuromylitis optica (nmo) or devics disease... It's very similar to MS

There are some people on this site with devics or NMO

Aquaporin 4 (AQP4) is a water channel protein found on cells known as astrocytes that surround the blood-brain barrier, (a layer of cells responsible for preventing dangerous substances in the blood from crossing into the brain). It is presumed that the blood brain barrier allows the AQP4 antibodies to enter the central nervous system. This causes an inflammation and demyelination and symptoms of a relapse.

Approximately 80% of people diagnosed with NMO have Aquaporin 4 antibodies in their blood.
I guess if your results are negative you might not have NMO

PS your english is great.. I used Google translate... Not sure if it works...

Es domāju, ka viņi cenšas izslēgt neiromilīta optica (nmo) vai devics slimību ... Tas ir ļoti līdzīgs MS
Šajā vietnē ir daži cilvēki ar devics vai NMO
Aquaporin 4 (AQP4) ir ūdens kanāla proteīns, kas atrodams šūnās, kas pazīstamas kā astrocytes, kas ieskauj asins-smadzeņu barjeru (šūnu slānis, kas atbild par bīstamu vielu nokļūšanu asinīs no smadzenēm). Tiek pieņemts, ka asinsvada smadzeņu barjera ļauj AQP4 antivielām iekļūt centrālajā nervu sistēmā. Tas izraisa iekaisumu un demielinizāciju un recidīvu simptomus.
Apmēram 80% cilvēku, kuriem diagnosticēta NMO, ir asinis ar Aquaporin 4 antivielām.
Es domāju, ja jūsu rezultāti ir negatīvi, iespējams, ka jums nav NMO
PS jūsu angļu valoda ir lieliska