Upon contact, you lose health but gain one to three coins (two to four coins with the PHD); each one could be any type of Coin; a Penny, a Nickel, or rarely, a Dime.
With the Wrath of the Lamb DLC the Blood Donation Machine is also capable of dropping an IV Bag instead of a normal Blood Bag. There is a 50% chance for an IV Bag to be dropped instead of a Blood Bag.
Alternatively, you can destroy it with a bomb. This will destroy the Blood Donation Machine and give you a random drop of hearts and/or money rather than the IV Bag or Blood Bag.
NotesIt is possible to be killed by the Blood Donation Machine. In levels before The Womb, the machine will take a half-heart of health with each use. From The Womb and onwards, however, the machine will start taking one full heart and will ignore your Soul Hearts. It is possible to find multiple Blood Bags in a single playthrough. The IV Bag, however, cannot show up once you have touched it (picked it up). As the invincibility time on Isaac becomes longer if he takes a full heart of damage, it is possible to use the Blood Donation Machine twice for one heart in The Womb and onwards, if the player is quick enough. As with all health-up items when playing with ???, the Blood Bag only adds one Soul Heart, making the Blood Donation Machine a bad trade option in general without the right items (see next note). There are many items that synergize with the Blood Donation Machine: The machine is triggered upon touch, so items that provide invincibility like My Little Unicorn, Book of Shadows or The Gamekid and A Pony allow using it for free. Prior to The Womb, having the Bloody Penny will give you a good chance of replenishing your health loss for every use of the machine. This is especially effective if you have good luck, and get multiple coins per use. With The Habit, you can easily charge your activated items. If these provide you with new health, you can easily acquire high amounts of money and possibly even further health. These health-combos even work in The Womb, Sheol, Cathedral, and Chest if you use the strategy from the previous note of timing the second Blood Machine use during your invincibility 'grace time'. Yum Heart, Charm Of The Vampire, and Little C.H.A.D. are useful, as these can create several hearts worth of health per level which can be spent on the machine. In Wrath of the Lamb, Child's Heart is also very useful for the same reason. Yum Heart, with the The Habit, allows you to get infinite money until the machine blows up. Whore of Babylon is great if you have Soul Hearts because it allows you to lower your health to half a heart while keeping your soul hearts. Additionally, right after the item is activated (when you get down to a half-heart) you can quickly use the Blood Donation Machine again (Sometimes even a second time with perfect timing) without it removing your final half-heart, because the invincibility time granted by activating the Whore Of Babylon is much longer than usual. Trinkets Such As The Cartridge Can Proc, Giving Temporary Invincibility. To Exploit The Blood Bank Is Very Easy Doing This
Strategies for obtaining a Blood Bag / IV Bag
Every time you use a Blood Donation Machine, there is a 1/15 (6.66%) chance that the machine will explode into either the Blood Bag or IV Bag. This risk should be considered when pursuing the Blood Bag. However, it will not only grant an extra heart container, but it will also heal five hearts (thereby covering the cost of getting it in pre-womb levels). If the player enters an Arcade with enough pennies, it is almost guaranteed that a Blood Bag can be attained, as you can donate and then use the pennies on the other games to restore life to donate more. This method is especially effective when possessing the Lucky Foot, as winning at the Shell Game becomes a 50% chance. Should the player run too low on hearts, they can bomb it to try and replenish some of their spent health.
As of Wrath of the Lamb, gambling for a Blood Bag has become a lot more risky, since there is a 50% chance for the IV Bag to drop. However, unlike the Blood Bag, the IV Bag will not drop if you have previously picked it up. You can still find multiple IV Bags if you fail to actually pick it up when it spawns.