Take a look at whether a perk says that it GIVES you regeneration, or that it INCREASES it. Big difference. For example, the Regeneration perk in Athletics gives a small amount of health per second without needing to take any other items or perks. The "Rapid Bloodflow" perk in Cold Blood only increases the regeneration other items and perks give you. If you take "Bounce Back" the medical item that gives you health regeneration in a fight, Cold Blood will dramatically increase how much regeneration it will give you. Still not enough to offset the lack of Armor/Resistance/Evasion V has from game bugs, but it does help make you much more durable in a fight none the less.