You may need a different detergent or a detergent booster that works harder on stains. Usually they're peroxide based, but contain other agents as well. Some come in powder form and others in sprays.

One powder I grabbed does brighten better than detergent alone and makes things smell like an honest-to-goodness laundry. (Which I'm not going to name because this already sounds like a sales pitch. It isn't. It's just something that was on special offer on my supermarket's website and I added it to my virtual basket because I have a few blood-spotted items of clothing that regular washing wasn't getting out.)

It worked wonders on some very greyed white t-shirts, but not so great on the blood spots on coloured clothing. I may need to soak them for longer or use more additive, risking the colour, which I may have been too cautious about up to the present.