Does the blood content in our body decrease after we donate blood?

Approximately 450 mL (1 pint) of blood is collected during a blood donation, which is less than 10% of your total blood volume. Your body keeps on replenishing blood all the time whether you give blood or not, so this amount is quickly replaced.

To be exact, the plasma portion of a donation is replaced within hours, the platelet portion within days and red blood cells in about 56 days.

(This is why blood donors cannot give more often than once every 56 days.)