Singaporeans were informed on Feb. 14 that the Singapore Red Cross was running low on stock for a number of blood types.

The A+, B+, O+ and AB+ blood types were at critical levels, which meant that donors were urgently needed and urged to donate on the same day.

The good news is that within three days, all four blood types saw an increase after blood donors in Singapore responded to the call for donations.

Here's a gif showing the increase by Feb. 17 as a result of donations, three days after the appeal was made:

Overall, six out of the eight blood types saw an increase in the blood bank, with B- and O- also registering increases.

However, two of the blood types, A- and AB-, have since fallen in stock.

AB- fell from the low to critical levels.

Low levels mean that donors are urged to donate within the week.

The reason for this perpetual shortage could be because the AB- blood type is regarded has one of the rarest blood types in the population.

The donor pool is already very small, as possibly fewer than 1 percent of a given population has the AB- blood type.

In the United States, for example, only 0.6 percent of the population has the AB- blood type.

AB+ has a greater number of donors, but it is still relatively fewer than the rest of the A, B and O blood types, according to the Red Cross Singapore data.

So, if you're an AB blood type person in Singapore, your donation will come in very handy.

Facts about blood donation in Singapore

Just 1.87 per cent of Singapore’s resident population, or 75,655, are blood donors.

According to Red Cross Singapore, one unit of blood can save three lives.

Every hour of the day, 15 units of blood are used here.

About 120,000 units of blood are needed to meet the transfusion needs of patients every year, equivalent to more than 400 units of blood a day.

HSA told Today that it was important to maintain at least six days of blood stock at all times for daily transfusion needs and bleeding emergencies in Singapore.