The Blood Channeling feature of the Blood Magic Wizard from Tal’dorei Campaign Setting: Reborn says:
When casting a wizard spell that requires a costly material component, you can forego the component by taking 1d10 necrotic damage per 50 gp of the cost of the component (minimum 1d10). This damage can't be reduced in any way. If this damage reduces you to 0 hit points, the spell fails but the spell slot is not expended.
The Player's Handbook, Ch. 10, says:
Whenever you take damage while you are concentrating on a spell, you must make a Constitution saving throw to maintain your concentration. The DC equals 10 or half the damage you take, whichever number is higher. If you take damage from multiple sources, such as an arrow and a dragon’s breath, you make a separate saving throw for each source of damage.
If you are not concentrating on anything before you use this feature to cast a spell, and you use this feature to forego the component cost of a spell that requires concentration, does the necrotic damage taken from doing so cause you to make a Constitution saving throw to maintain your concentration? (Put another way, are you already concentrating by the time you take the Blood Channeling damage?)