Insulin is a peptide hormone produced by the beta cells of the pancreas. Its primary role is to regulate blood glucose by facilitating the uptake of glucose into cells — particularly muscle, fat, and liver cells — where it is used for energy or stored as glycogen or fat. Insulin also suppresses glucose production by the liver and promotes protein synthesis and fat storage.
Measuring insulin levels helps assess pancreatic function and insulin sensitivity. Elevated insulin in the presence of normal blood glucose indicates insulin resistance — the pancreas is working harder than it should to maintain blood sugar in range. Very high insulin can also cause hypoglycaemia (low blood sugar) and may indicate an insulinoma. Insulin testing is most informative when combined with fasting glucose to calculate HOMA-IR.
FAQs
What is the difference between fasting insulin and random insulin?
Fasting insulin measures the baseline pancreatic output after 8-12 hours without food, reflecting insulin sensitivity. Random or post-meal insulin reflects the postprandial secretory response. Fasting insulin is most clinically informative for metabolic health assessment.
Can insulin testing diagnose an insulinoma?
Yes. An insulinoma (insulin-secreting pancreatic tumour) causes inappropriately elevated insulin during hypoglycaemia. The key diagnostic finding is elevated or non-suppressed insulin during symptomatic hypoglycaemia. Supervised 72-hour fasting with serial glucose, insulin, C-peptide, and proinsulin testing is the standard diagnostic protocol.
Does fasting insulin change quickly with lifestyle improvements?
Yes. Improvements in insulin sensitivity are measurable within weeks of dietary change and exercise. A single bout of exercise can lower fasting insulin measurably for 24-48 hours. Sustained 8-12 weeks of lifestyle change produces lasting fasting insulin reductions.
Should insulin testing be part of routine health checks?
Fasting insulin is not yet part of standard routine screening in Australia but is increasingly included in comprehensive metabolic and preventive health panels. In people with risk factors for metabolic syndrome or type 2 diabetes, fasting insulin adds important information beyond standard glucose and HbA1c testing.
