A. GLUCOSE CONTROL TESTS
1. HbA1c (Glycated Hemoglobin)
What it measures: HbA1c measures the percentage of hemoglobin (the oxygen-carrying protein in red blood cells) that has glucose permanently attached to it. Because red blood cells live for about 2 to 3 months, HbA1c reflects a weighted average of blood glucose over roughly the past 2 to 3 months — more heavily influenced by more recent weeks than by months ago.
Why it's needed: It is the single most important test for judging how well diabetes is controlled overall, since day-to-day finger-prick readings only capture single moments, while HbA1c smooths those out into a long-term picture. It is used both to diagnose diabetes and to guide treatment decisions.
How often: Every 3 months if blood sugar control is not yet at target or medications have recently changed; every 6 months if control is stable and at target. Note: conditions that affect red blood cells (anemia, recent blood transfusion, thalassemia, certain hemoglobin variants, kidney failure/dialysis) can make HbA1c inaccurate, so your doctor may use other measures in those situations.
2. Fasting Plasma Glucose / Random Blood Glucose
What it measures: The actual glucose concentration in the blood at a single point in time — either after an 8-hour fast or at a random moment.
Why it's needed: It gives a real-time snapshot, useful for diagnosis, for spotting acute highs or lows, and for day-to-day treatment decisions, complementing the longer-term picture from HbA1c.
How often: Home self-monitoring frequency depends on treatment: people on multiple daily insulin injections may check several times a day; people on oral medications only may check less often, sometimes just periodically or when symptoms suggest a problem. Your doctor will set a monitoring schedule matched to your specific treatment.
3. Fasting C-peptide and Fasting Insulin
What it measures: C-peptide is a byproduct released in equal amounts to insulin when the pancreas manufactures its own insulin, making it a reliable marker of how much insulin your own pancreas is still producing (unlike directly measuring insulin, C-peptide isn't affected by insulin injections, since injected insulin doesn't come with C-peptide attached). Fasting insulin measures the insulin level directly.
Why it's needed: This test is not about tracking day-to-day sugar control — it's about understanding how much natural insulin-producing capacity a person still has. It helps distinguish type 1 from type 2 diabetes, helps predict how well someone is likely to respond to oral medications that stimulate the pancreas (like sulfonylureas), and is useful as a baseline if "secondary failure" (a medication that used to work well suddenly stops working) is suspected later on, since repeating the test can show whether beta-cell function has declined further.
How often: Typically done once at diagnosis or when starting certain treatments (as a baseline), not as a routine repeated test. It may be repeated later specifically if blood sugar control worsens unexpectedly despite a previously stable regimen, to help figure out why.