The reference level of normal blood sugar in a laboratory test is 4.0–6.0 when fasting and below 7.8 mmol/l after a meal. If you check the blood sugar level in a blood sample you take from your fingertip with a rapid meter, bear in mind that the accuracy of the measurement is ±15 percent. When the blood sugar drops lower than normal (3,9 or lower) it is called a hypoglycaemia i.e. low blood sugar.
The blood sugar level of a healthy person does not normally drop below 3.5 mmol/l. If a person exhibits symptoms of low blood sugar, the first thing to check is that their blood sugar levels are actually low at the same time. If this is the case, is time to investigate the reason for the low blood sugar levels. Usually, the underlying reason is a dysfunction of the hormones that regulate blood sugar.
The most common reason for a slightly low blood sugar of 3.0–3.9 mmol/L is reactive hypoglycaemia:
A few hours after eating, a person exhibits symptoms of low blood sugar, such as a feeling of hunger, trembling, shakiness, heart palpitations and sweating. The symptoms go away when something sugary is eaten.
In most cases, the underlying cause is stronger than usual secretion of insulin from the pancreas, triggered by eating carbohydrates that quickly raise the blood sugar level. Insulin’s blood sugar-raising effect carries on after the fast-acting carbohydrates have ceased to increase the blood sugar level, resulting in a quick drop in blood sugar.
The treatment is to avoid fast-acting carbohydrates and eat fibre-rich carbohydrates instead.
Following weight loss surgery, also known as bariatric or metabolic surgery, there may be a tendency for blood sugar to drop after a meal. Heavy alcohol consumption, liver or kidney disease, some pharmaceutical products or eating disorders may also cause blood sugar to drop lower than normal.
If, in addition to symptoms of low blood sugar, the blood sugar level is discovered to be below 3 mmol/l, the person in question is referred to specialized medical care for further examinations. An insulin-producing tumour or adrenal insufficiency are rare causes of hypoglycaemia.