(Undated) -- As summer starts to wind down, local blood supplies tend to wind down as well. Jill Moeggenberg with Heartland Blood Centers says they need approximately 550 units of a blood a day, and she calls the need for donors "urgent." While hospitals need blood supplies on hand throughout the year, she says summer is an especially difficult time. Donors must be in good health, weigh at least 110 pounds and be age 17 or older - or 16 with parental consent. Moeggenberg says it’s important to call first with questions about your eligibility to donate, especially if you are taking medication of any kind.