Magkaiba po yun. FBS is checking your BS level with at least 8hrs fasting. Yan ung normal daily BS level mo. Pag mataas FBS, sunod ipapagawa sayo HbA1c. OGTT naman is 8hrs fasting then papainumin ka ng glucose drink then kukuhaan ng blood after 1hr & 2hrs. Chinecheck namam jan kaano kabilis mag spike ang BS mo and how fast your body can burn sugar in 1hr and 2hrs. Ginagawa yan to check if need mo ng addtl work ups for BS monitoring or hindi.
Pareho nmn pong pra sa sugar at need magfasting. Iba nga lang po yunv process.