The American Red Cross has issued an emergency call for blood and platelet donors, reporting that its supply of most blood types dropped below its five-day goal to less than three.

The request came about three weeks after Penn Medicine Lancaster General Health Blood Donor Center asked donors of certain blood types to help replenish its supply.

Here are three things to know.

Beyond summer slump

Donations traditionally slump as people take summer vacations, but Lancaster General spokeswoman Mary Ann Eckard said its need was accentuated by an increase in trauma cases, which pushed blood use up about 20% in May and June.

According to LNP records, local traumas since the end of April included four people killed and 15 others injured in shootings and stabbings in Lancaster city.

Red Cross said its shortage comes “after a difficult July Fourth week” in which it got 17,000 fewer donations than needed nationally and about 300 fewer than needed in the Pennsylvania region including Lancaster County.

People responded, need continues

Lancaster General reported that the second half of June brought a roughly 25% increase in donors. Its inventory is currently adequate, although it always encourages regular donations.

The Red Cross said a recent survey found just 3 out of 100 people in the U.S. donate blood each year, and the number of new blood donors has decreased since 2014.

Shortages are becoming more common, according to the organization, which noted that this past May it issued the Red Cross’s “first-ever type specific appeal when the supply of type O blood dropped below a two-day supply.”

Red Cross also said an recently concluded two-day drive at Pennsylvania Renaissance Faire in Lancaster County is one of its annual signature events and has collected close to 3,400 pints of blood since 2006.

How to give

To donate, people must be at least 16 years old; weigh at least 110 pounds; be in good health, with no recent major surgery; have no history of hepatitis; and not have gotten a tattoo or body piercing within the last 12 months.

Here’s where to find blood drive schedules and information on donating: