Random Blood Glucose: Normal Range and Meaning

A random glucose is a blood sugar measured without any rule about fasting. It may be taken from a vein in the laboratory or from a finger-prick in a clinic, pharmacy or at home. Lab Tests Online UK says that for random and timed tests you should follow the instructions given by your healthcare professional, whereas for screening a fasting sample of at least 8 hours is generally recommended.

Because glucose rises after food and falls between meals and with activity, a random value is affected by what you ate and when. Lab Tests Online UK notes that blood glucose rises slightly after a meal and that insulin is released to bring it back down. The same number can therefore be unremarkable shortly after lunch and unexpected first thing in the morning.

For people without diabetes, the UK sources read here do not set out a single upper "normal" for a random result. What they give is the level at which a random reading is treated as indicating diabetes, and the fasting and glucose tolerance bands, which are more precisely defined.

A random reading well below 11.1 mmol/L is below the line at which these sources describe diabetes. A reading above it, particularly with symptoms, is a reason to arrange confirmation.

Lab Tests Online UK says high levels of glucose most frequently indicate diabetes, but many other conditions can raise glucose, including acute stress such as trauma, heart attack or stroke, long-term kidney disease, Cushing syndrome, hyperthyroidism, pancreatitis and drugs such as corticosteroids, diuretics, oestrogens, lithium and aspirin. A single high reading taken while someone is acutely unwell therefore needs to be interpreted with care.

If you do not have symptoms, it also advises that the test should be repeated at a different time, for example fasting glucose, random glucose or HbA1c within two weeks. If you do have symptoms such as thirst, passing a lot of urine, tiredness and blurred vision, the position is different, and the NHS advises an urgent GP appointment or NHS 111 for any symptoms of diabetes.

Diabetes UK warns that wearable monitors sold for people without diabetes cannot be used to diagnose diabetes or prediabetes. Diagnosis can only be done by blood tests arranged by a GP.

Diabetes UK describes a hypo as a blood sugar level dropping too low, usually below 4 mmol/L. Lab Tests Online UK lists symptoms as sweating, hunger, trembling, anxiety, confusion and blurred vision, and notes that a diagnosis of hypoglycaemia needs low glucose, symptoms and reversal of those symptoms when glucose is restored.

In people without diabetes, low glucose can occur with causes such as drinking alcohol, starvation, extensive liver disease, hypopituitarism, hypothyroidism and adrenal disease, according to the same source. Persistent or recurrent episodes need medical assessment to find the cause.

HbA1c is the commonest follow-up because it reflects average glucose over the previous 2 to 3 months. Lab Tests Online UK says the WHO recommends it can be used to diagnose type 2 diabetes, but that it cannot be used in some situations, including children with symptoms, pregnancy, suspected type 1 diabetes, symptoms for less than 2 months, some haemoglobin variants, anaemia and recent blood transfusion. In those cases an oral glucose tolerance test is used instead.

If HbA1c is 48 mmol/mol or over, Lab Tests Online UK says a symptomatic person is confirmed, whereas an asymptomatic person needs repeat testing within 4 weeks. If your result falls in the prediabetes band, the NHS says you may be eligible for the NHS Diabetes Prevention Programme, which helps people make lifestyle changes.

• Note when you last ate and any recent illness, steroids or other medicines.

• Report thirst, frequent urination, weight loss, tiredness and recurrent infections.

• Expect a fasting glucose, HbA1c or repeat reading to confirm an unexpected value.

• If you already have diabetes, use the targets your own team has agreed rather than general ranges.