low sugar blood test explained

Overview

A low blood sugar test measures the amount of glucose (sugar) in your blood. Glucose is your body's main source of energy. When your blood sugar drops too low, it is called hypoglycemia. This test helps find out if your blood sugar level is below the normal range.

Low blood sugar is common in people with diabetes who take insulin or certain diabetes medications. It can also happen in people without diabetes, though less often.

It affects people with diabetes, especially those using insulin or sulfonylurea medicines. It can also affect people with certain medical conditions, such as liver disease, kidney problems, or rare tumours, and can occur after heavy alcohol use or during prolonged fasting.

Symptoms

Common symptoms

• Shakiness or trembling
• Sweating
• Feeling dizzy or lightheaded
• Hunger
• Rapid heartbeat
• Irritability or mood changes
• Feeling weak or tired
• Blurred vision

Symptoms in children

• Irritability or crying
• Lethargy or unusual sleepiness
• Pale skin
• Clumsiness or trouble walking
• Complaints of feeling 'funny' or dizzy

Symptoms in older adults

• Confusion or disorientation
• Difficulty speaking
• Weakness or unsteadiness
• Dizziness or fainting
• Changes in behaviour that may be mistaken for dementia

Causes

Main causes

• Taking too much insulin or diabetes medication
• Skipping or delaying meals
• Exercising more than usual without adjusting food or medication
• Drinking alcohol on an empty stomach
• Certain medical conditions like liver or kidney disease

Risk factors

• Having diabetes and using insulin or certain oral diabetes drugs
• Being very physically active without adequate food
• Having a history of low blood sugar episodes
• Eating irregular meals or fasting
• Drinking alcohol, especially without eating

When to see a doctor

See a doctor urgently if:

• You have a blood sugar reading below 3.0 mmol/L and cannot bring it up with fast-acting sugar
• You experience severe symptoms like confusion, fainting, or seizures
• You have repeated low blood sugar episodes that interfere with daily life

Book a routine appointment if:

• You have mild symptoms that occur more than once or twice a week
• You have diabetes and are unsure how to adjust your medication or diet to prevent lows
• You do not have diabetes but experience symptoms of low blood sugar

Diagnosis

A healthcare provider will review your symptoms, medical history, and use a blood test to measure your glucose level. In some cases, they may ask you to fast for a period or do a test that tracks your blood sugar over several hours.

Tests that may be done

• Finger-prick blood glucose test – a quick test using a small drop of blood from your fingertip
• Venous blood glucose test – a blood sample taken from a vein in your arm, usually done in a lab
• Continuous glucose monitoring (CGM) – a small sensor worn on your skin that measures glucose levels throughout the day and night
• Oral glucose tolerance test (OGTT) – you drink a sugary liquid and your blood sugar is measured at intervals to see how your body handles sugar

What to expect at your appointment

Your doctor may ask you to keep a diary of symptoms, meals, and activities. For a blood test, you might need to fast (not eat or drink anything except water) for several hours beforehand. The test itself is quick and usually not painful. The results help your doctor understand if your blood sugar is too low and why.

Treatment

Treatment for low blood sugar aims to raise your blood sugar quickly and safely, and then prevent future episodes. The right approach depends on the cause and how often it happens.

Self-care at home

• If you feel symptoms, eat or drink something that contains fast-acting sugar, such as fruit juice, regular soda, a glucose tablet, or a handful of candy.
• After your blood sugar returns to normal, eat a small snack with protein and complex carbohydrates to keep it stable.
• Check your blood sugar again after 15 minutes to make sure it has risen.
• Carry a source of fast-acting sugar with you at all times, such as glucose gel or tablets.
• Teach family and friends how to recognise low blood sugar and what to do in an emergency.

Medical treatments

If you have diabetes, your healthcare provider may adjust your insulin or tablet dosage, change the timing of your meals or medications, or suggest a different treatment plan. For people without diabetes, treatment focuses on the underlying cause, such as managing liver or kidney problems or avoiding prolonged fasting. In severe cases, a glucagon injection may be prescribed for emergency use. This is a hormone that raises blood sugar quickly. Your doctor will train you and your family on how and when to use it.

When is surgery considered?

Surgery is not typically used to treat low blood sugar. However, in very rare cases where a tumour (such as an insulinoma) is causing low blood sugar, surgery to remove the tumour may be recommended.

Living with this condition

Living with low blood sugar means being aware of your body's signals and planning ahead. Check your blood sugar regularly if you have diabetes. Keep fast-acting sugar with you. Wear a medical ID bracelet that lists your condition. Tell friends, coworkers, and family what to do if you have a severe low.

Lifestyle tips

• Eat regular meals and snacks that include protein, healthy fats, and complex carbohydrates.
• Avoid skipping meals, especially if you take diabetes medication.
• If you drink alcohol, have it with a meal and check your blood sugar before and after.
• Adjust your food and insulin before, during, and after exercise.
• Keep a consistent daily routine to help prevent unexpected lows.

Diet and exercise

Eat balanced meals and snacks throughout the day. Include foods like whole grains, beans, vegetables, and lean protein. When you exercise, eat a small snack beforehand if your blood sugar is on the lower side. Check your blood sugar before, during, and after physical activity. Stay hydrated and don't exercise on an empty stomach.

Mental health and emotional wellbeing

Frequent low blood sugar can be stressful and cause anxiety about episodes happening unexpectedly. It can also affect your mood and sleep. It is important to talk to your healthcare provider about these feelings. Support groups and counselling can help you cope. Remember that managing low blood sugar is a skill that gets easier with practice.

Prevention

Many cases of low blood sugar can be prevented by careful planning. If you have diabetes, work with your healthcare team to find the right balance of medication, food, and activity. Always carry a source of fast-acting sugar. Check your blood sugar before driving or operating machinery. Avoid drinking alcohol on an empty stomach.

Screening programmes

If you have diabetes, your doctor will regularly check your blood sugar levels and may do a test called HbA1c to see your average glucose over the past few months. For people without diabetes, screening is not routinely done unless you have symptoms or risk factors.

Complications

If left untreated

• Severe confusion, unconsciousness, or coma
• Seizures
• Difficulty speaking or swallowing
• Increased risk of falls and accidents
• Long-term brain damage in very rare cases of prolonged severe hypoglycemia

Long-term outlook

Most people with low blood sugar can manage it well with education and a good care plan. With proper treatment and prevention, serious complications are uncommon. Learning to recognise early symptoms and acting quickly can keep you safe. Your healthcare team can help you live a full and active life.

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