What is the difference between hyperglycemia and hypoglycemia?
Side by side
| Hypoglycemia (low) | Hyperglycemia (high) | |
|---|---|---|
| Threshold | Below 70 mg/dL (3.9 mmol/L) | Above 180 mg/dL (10.0 mmol/L) after meals |
| Onset | Minutes | Hours to days |
| Classic signs | Shaking, sweating, hunger, anxiety, palpitations, confusion | Thirst, frequent urination, fatigue, blurred vision |
| Skin | Clammy, pale | Dry, warm |
| Danger | Immediate — seizure, unconsciousness | Over hours (DKA) and years (complications) |
| First action | Treat now: 15g fast carbohydrate | Test, hydrate, correct if prescribed |
The one that needs acting on fastest
Hypoglycemia. The brain runs on glucose and has essentially no reserve. Below 54 mg/dL (3.0 mmol/L) is a medical emergency regardless of how well you feel, and severe lows can cause seizures or loss of consciousness within minutes.
The treatment is the 15/15 rule: take 15 grams of fast-acting carbohydrate — glucose tablets, 4oz of juice or regular soda, or a tablespoon of honey — wait 15 minutes, and retest. Repeat if still below 70. Once above, eat something with protein or fat to prevent a second dip.
Chocolate and other fatty sweets are poor choices; the fat slows absorption when you need speed.
Why confusing them is dangerous
Both can cause dizziness, confusion, irritability and difficulty concentrating. Treating a low as if it were a high is genuinely dangerous.
If you take insulin or a sulfonylurea, test before deciding. If you cannot test and you feel shaky and sweaty, treat it as a low — the risk of briefly raising an already-high glucose is far smaller than the risk of leaving a low untreated.
Hypoglycemia unawareness
Some people, particularly after years with diabetes or after repeated lows, stop getting warning symptoms. The first sign becomes confusion or collapse. This is a specific and serious situation that needs review — it can often be improved by deliberately avoiding lows for a few weeks, and continuous glucose monitoring with alarms makes a real difference.
Who gets which
Hypoglycemia is mainly a risk for people taking insulin or sulfonylureas. Metformin alone rarely causes it. Hyperglycemia can happen to anyone, including people with no diabetes diagnosis at all, during illness or on steroids.
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