Written by: If you're undergoing diabetes screening, your package will likely include both a Fasting Blood Sugar (FBS) test and an HbA1c test. While both check how your body is handling glucose, they measure different parameters. Understanding the difference between these tests is key to interpreting your reports accurately.
Review ADA diagnostic cutoffs, 3-month average glucose correlation, and fasting guidelines. Read our detailed Diabetes Care Knowledge Hub or check your levels with the HbA1c Blood Test.
1. Fasting Blood Sugar (FBS)
This test measures the amount of glucose circulating in your blood after an 8 to 12-hour fast (usually overnight).
- Pros: Fast, inexpensive, and excellent for showing your immediate metabolic state.
- Cons: A snapshot in time. If you ate a high-sugar meal the night before, or slept poorly, your fasting sugar can spike temporarily.
- Normal Range: 70 to 99 mg/dL.
2. HbA1c (Glycated Hemoglobin)
This test measures the percentage of your red blood cells' hemoglobin that is coated with glucose, reflecting your average blood sugar over the past 2 to 3 months.
- Pros: Cannot be manipulated by short-term changes in diet. Shows long-term control.
- Cons: Can be altered by conditions that affect red blood cell lifespan, such as anemia.
- Normal Range: Below 5.7%.
Why Both Matter
Your doctor will often look at both. For example, a patient might have a normal fasting glucose of 95 mg/dL but an HbA1c of 6.2% (pre-diabetes). This indicates that while their fasting state is managed, their blood sugar rises significantly after meals, suggesting the need for lifestyle adjustments.
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