It is sufficient if you have fasted 2 to 4 hours prior to the blood withdrawal. A 12-hour fasting is not mandatory for IgG tests. However, you should bear in mind that blood samples taken shortly after a meal are often lipemic and show a considerably worse test variance. We therefore recommend that the last meal eaten before the blood withdrawal should not have been a fatty meal. In practice, this means: There is no problem if, for example, you have had a normal breakfast at 8 o’clock and come for the blood withdrawal at 11:00. Yet it is not advisable if you have had a heavy lunch at 1 o’clock and come for the test at 2.30.