What hypoglycemia is and how to recognize it

Hypoglycemia means a blood glucose level that is too low for what the body needs. In type 1 diabetes, any value below 70 mg/dL (3.9 mmol/L) counts as hypoglycemia [1]. It is not a separate disease, but an unwanted effect of insulin treatment. It happens when the insulin present in the body exceeds what is needed at that moment.

The body runs on a fairly steady glucose level, because the brain depends on it almost entirely. When blood glucose falls, the body sets off an alarm (hormonal and neurological) and you feel the first signs. Hypoglycemia is treated straight away, with fast-absorbing carbohydrate [1]. It is the situation in diabetes where you have to act fastest, as the figure below shows.

The threshold is 70 mg/dL (3.9 mmol/L). Below this value we speak of hypoglycemia, whether or not you feel anything. The figure is not chosen at random, because at roughly this level the body of a person without diabetes starts to release defense hormones, mainly glucagon and adrenaline [1].

This threshold is an alert value, not a danger value. It warns you that you have to act now, so that you do not go any lower. At 68 mg/dL (3.8 mmol/L) the brain still has enough glucose. The problems appear lower down, and the point of the threshold is to stop you before you get there [1].

There are three. Level 1 means a blood glucose between 54 and 69 mg/dL (3.0–3.8 mmol/L). Level 2 means a blood glucose below 54 mg/dL (3.0 mmol/L). Level 3 is severe hypoglycemia, defined by the need for someone else's help [1].

The classification is used the same way all over the world, which helps when you compare your results or talk to another doctor. The first two levels are defined by a number, the third by what happens to you. That is why a severe hypoglycemia can occur at a value that, on paper, looks like level 1.

It is the name given to level 2, that is, a blood glucose below 54 mg/dL (3.0 mmol/L). From this value the brain starts to receive too little glucose, and the signs are no longer only an alarm. Difficulty concentrating, blurred vision or slurred speech may appear. This is the point where correcting the hypoglycemia can no longer be put off [1].

A level 2 episode is not overlooked even after it has been corrected. One or more such episodes call for a discussion with your doctor about insulin doses and about the shape of the day [1]. If you go below this threshold without feeling anything, the information matters even more. It usually means you have lost the body's warning signs.

The first signs come from the sympathetic nervous system: shakiness, cold sweat, palpitations, sudden intense hunger, edginess. These are useful signals, because they appear before brain function is affected.

If blood glucose falls further, the signs that come from the brain appear: difficulty concentrating, blurred vision, slurred speech, irritability, drowsiness. At this point it is already hard to help yourself, so treatment must not be put off [1].

Yes. The definition rests on the measured value, not on what you feel. A blood glucose below 70 mg/dL (3.9 mmol/L) counts even when you feel perfectly normal [1]. The reason is that many patients with diabetes have a weakened defense response, so the absence of symptoms does not mean the absence of risk.

The situation deserves attention especially below 54 mg/dL (3.0 mmol/L). A value that low with no symptom at all is a sign of impaired awareness of hypoglycemia. It does not show that you have become resistant to low values. It shows that your alarm system no longer starts in time.

It is the situation where you have all the signs of a hypoglycemia, but the measured blood glucose is normal. It appears in patients with diabetes who are used to high values, when blood glucose comes down quickly toward normal. The body has adapted to the high values and treats 120 mg/dL (6.7 mmol/L) as a dangerous fall. The symptoms are real, not imagined.

Treating with glucose is not the answer, because blood glucose is already where it should be, and hypoglycemia is defined by the measured value [1]. Measure every time before you decide, though, and if the symptoms get worse repeat the blood glucose with the meter. If you eat every time you feel like this, you stay stuck at high values. The body's alarm threshold comes down on its own over a few weeks, as the average glucose falls. It is a passing stage at the start of better treatment.

The cause is always an imbalance between the insulin available in the body and what the body needs at that moment. Most often it is an insulin dose that was too large, a meal that was delayed or smaller than you estimated, or a correction given too soon after the previous one. If the lows keep coming back with no explanation in doses, meals or activity, your doctor looks for an added cause, such as celiac disease, adrenal insufficiency or kidney impairment.

Physical activity increases insulin sensitivity and can lower blood glucose even several hours after a workout [2]. Alcohol blocks the liver's production of new glucose, so it can raise the risk of hypoglycemia for 24 hours [3]. The risk is greatest when the liver's stores are already empty, that is on an empty stomach or after exercise.

Yes, but rarely. In a person without diabetes there are three safety mechanisms that almost always stop an uncontrolled fall in blood glucose. The first is that the body's own insulin secretion shuts off. The second is the release of glucagon, the hormone that pulls glucose out of the liver. The third is adrenaline, which steps in when the first two are not enough. Together, these mechanisms keep blood glucose above the risk threshold in ordinary conditions.

In type 1 diabetes none of these three mechanisms works the same way any more. The insulin you take acts whatever the blood glucose value is. The glucagon response is lost in the first years of the disease, and the adrenaline response weakens after repeated episodes [1]. This is where the real difference lies. You are not more fragile than other people, you have lost protective mechanisms that they use without knowing it.

Hypoglycemia is severe (level 3) when you need someone else to help you. The symptoms are more advanced and consist of marked confusion, inability to swallow, seizures and loss of consciousness. The definition does not refer to any particular blood glucose figure, but to the fact that you can no longer treat yourself [1]. A blood glucose of 40 mg/dL (2.2 mmol/L) that you treated on your own is not a severe hypoglycemia. One of 60 mg/dL (3.3 mmol/L) where you needed help is.

If the person has lost consciousness, nothing is given by mouth, because food or liquid can reach the lungs. Glucagon is given (nasal or injectable) and the emergency services are called immediately. In type 1 diabetes, the risk of severe hypoglycemia will be there for the rest of your life, so it is worth always keeping fast-acting carbohydrate within reach and having a plan for emergencies [4].

Yes, the 70 mg/dL (3.9 mmol/L) threshold is the same for a child, a teenager and an adult. The physiology does not change with age. What differs is the ability to recognize the episode and to react in time [1].

In children under 6 the problem is not the threshold, but communication. A small child does not say that they are having a hypoglycemia and often does not even recognize the feeling. That is why at this age what the adults around them notice matters a great deal, along with monitoring using a glucose sensor. Glucose targets are chosen individually, taking this risk into account [1].

Repeated episodes of hypoglycemia over the past days or weeks get the body used to low values, and it no longer triggers the warning signals. You do not need many years of diabetes for this, because two or three recent episodes can be enough. You can reach very low blood glucose levels without feeling anything, and the first sign may be confusion itself. This is impaired awareness of hypoglycemia [5].

The good news is that it can be regained. If you carefully avoid hypoglycemia for a few weeks, the level at which symptoms appear rises again. This is one of the reasons to discuss temporarily more relaxed targets with your medical team [5].

Mild episodes are a normal part of insulin treatment and happen to most people, a few times a week. They settle on their own with fast-acting carbohydrate and leave no lasting harm. What counts, though, is not their number but the time spent below the threshold, which your sensor shows you.

For most adults and children with type 1 diabetes, the international target is less than 4% of the day spent below 70 mg/dL (3.9 mmol/L), which is about one hour, and below 54 mg/dL (3.0 mmol/L) the target is less than 1% [1]. For older people and those at high risk the target is stricter, less than 1% of the day spent below 70 mg/dL (3.9 mmol/L) [1]. Severe episodes are far rarer, but they do not disappear with experience, and the risk is present at every stage of type 1 diabetes [4]. That is why it matters to know in advance what to do, rather than improvising at the time.

At night you are asleep and it is much harder to feel the warning signs, so an episode of hypoglycemia can sometimes last for hours. Nighttime hypoglycemia occurs mainly after a day with more physical activity, because the muscles are replenishing their stores and keep taking up glucose long after the workout has ended [6].

This is where alarms matter most. A sensor that sounds before blood glucose drops too low turns a long episode into a short one. Alarms during the night really do catch the episodes that would otherwise go unnoticed [7].

Yes, and this is one of the most useful features of a glucose sensor [7]. If your symptoms do not match the value on the screen, confirm with a finger-prick meter before treating. Bear in mind that the sensor measures the glucose concentration in the fluid between the cells (interstitial fluid) and lags a few minutes behind blood.

Systems that automatically stop insulin delivery when they predict a fall to a preset target reduce the number of hypoglycemic episodes even further [8]. Alarm thresholds and settings are decided together with your medical team, because an alarm set too low leaves you no time to react.

In the short term there are the risks of accidents: falls, fractures, dangerous situations while driving or at work. Hypoglycemia can also trigger heart rhythm disturbances, especially during the night [9].

In the long term, fear of hypoglycemia can set in, and it is unfortunately quite common. Sometimes you fall prey to it and start keeping your blood glucose deliberately too high, eating extra and avoiding physical activity [10]. Analyses of the causes of death in adults with diabetes show that severe episodes of hypoglycemia are worth preventing, because they can sometimes be fatal [11].

Call the emergency services immediately if someone with hypoglycemia cannot swallow, does not respond or has seizures. Do not give them anything by mouth and give glucagon, if you have it to hand. The practical steps are on the page about treating hypoglycemia, and the situations that call for emergency care are listed in the medical disclaimer.

Contact your medical team the same day if you have had a severe episode, if you have repeated episodes with no explanation or if you have noticed that you no longer feel the warning signs. These are situations that call for a review of your treatment plan, not a correction on the spot [1].