Easy as!
Fungus is a dermatophyte and can be 'bred' on a dextrose plate or similar by any microbiologist at any uni or find one in the yellow pages...they test for food bacteria and what type of foot fungus someone has.
Eczema is sterile. Breeds nothing. It is simply the histamine reaction to an internal allergy. Like Candida in the intestines or yeast in the nose or vagina....
If you watch CSI, you will see them do this...
You don't need a doctor, you need a CSI! or just a microbiologist.
Itchy? you say...more likely to be a dermatophyte.