Could Ferisitm give a false positive pregnancy test?

No. Feristim, which is a supplement that contains iron, folic acid, vitamin B12, and other nutrients, should not affect your pregnancy test results.

Pregnancy tests detect the presence of the hormone hCG (chorionic gonadotropin) in the urine or blood, which is produced by a woman's body during pregnancy. Iron and vitamin supplements, such as Feristim, have no ingredients that can affect hCG levels or falsify pregnancy test results. Therefore, it is not possible for the preparation to be responsible for the positive test result.

I encourage you to read:

https://www.gdziepolek.pl/artykuly/test-ciazowy-jaki-wybrac-i-kiedy-zrobic

Feristim can be purchased at an online pharmacy:

https://www.gdziepolek.pl/produkty/106008/fertistim-dla-mezczyzn-proszek-do-wytworzenia-plynu/apteki

In cities such as Warsaw, Wrocław, Katowice, Kraków, Lublin, Gdańsk, Łódź, Szczecin, Białystok, Poznań and Chorzów, products can be ordered with instant delivery in as little as 1 hour thanks to the Wolt Drive service.

https://www.gdziepolek.pl/koszyk/szybka-dostawa?src=zf