A white mark or marks on a nail are called leukonychia and are not a cause for concern. It’s likely that you’ve injured the nail bed, right at the base of the nail where the new nail grows from, and this tiny trauma has left its mark. This can be the odd knock or bang, tight shoes where toes are concerned, or even some types of manicure or pedicure. This does not relate to any dietary deficiencies, as is commonly believed, so you do not need any tests. You just need to wait for that part of the nail to grow out, which can take a good few months, as fingernails take a month to grow 3.5mm.
There is nothing contagious about white marks on the nails. If the nails are completely white across the top or throughout, this can point to other conditions including fungal nail infection, which can be contagious.
You do not need to see a doctor about this and you do not need any tests. If you are unsure about the diagnosis or have specific concerns, if marks are persistent or recurring without an obvious cause, you could book a routine appointment for your doctor to ask you questions and examine you.
There is no reason you can’t work with white marks on your fingernails.