From the Guidelines
A fasting insulin level is not routinely recommended for general diabetes screening, but it may be useful in specific situations such as evaluating insulin resistance, metabolic syndrome, or prediabetes in patients with risk factors, as well as investigating hypoglycemia, polycystic ovary syndrome (PCOS), or acanthosis nigricans, as stated in the 2023 guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus 1. When considering the measurement of fasting insulin levels, it is essential to weigh the benefits and limitations of this test. According to the most recent guidelines, routine testing for insulin or proinsulin is not recommended for most people with diabetes or at risk for diabetes or cardiovascular disease, as these assays are useful primarily for research purposes 1. However, there are specific situations where fasting insulin levels may be valuable, such as:
- Evaluating insulin resistance, metabolic syndrome, or prediabetes in patients with risk factors like obesity, hypertension, dyslipidemia, or a family history of diabetes
- Investigating hypoglycemia, as the diagnosis of an islet cell tumor is based on the persistence of inappropriately increased plasma insulin concentrations in the face of a low glucose concentration 1
- Differentiating between type 1 and type 2 diabetes in ambiguous cases, where C-peptide measurements may be helpful 1
- Assessing women with polycystic ovary syndrome, although it is unclear whether measuring insulin resistance through insulin or C-peptide measurement has any advantage over assessing physical signs of insulin resistance 1 It is crucial to note that fasting insulin levels should be measured after an 8-12 hour fast, typically in the morning before any food or medication intake, and that the test is particularly useful when combined with fasting glucose to calculate HOMA-IR (Homeostatic Model Assessment for Insulin Resistance) 1. Ultimately, the decision to measure fasting insulin levels should be based on individual patient needs and clinical judgment, taking into account the latest guidelines and recommendations 1.
From the Research
Fasting Insulin Level Recommendations
A fasting insulin level is recommended in various situations, including:
- To evaluate insulin resistance, particularly in subjects with abnormal glucose tolerance 2
- As a practical indicator of the insulin resistance syndrome, a frequent risk factor for atherosclerosis in industrialized countries 3
- In individuals with impaired glucose tolerance or dysmetabolism to assess the risk of developing type 2 diabetes 4
- To assess the association with risk of development and presence of clinically overt cardiovascular diseases caused by atherosclerosis in individuals with normal blood serum level of glucose in fasting state 5
- As a potential non-medicinal treatment option for patients with type 2 diabetes, with intermittent fasting protocols showing promise in reducing body weight, decreasing fasting glucose, and decreasing fasting insulin 6
Key Considerations
When considering a fasting insulin level, the following points are important:
- Fasting insulin level is a reliable marker of insulin resistance, particularly in subjects with normoglycemia 2
- Elevated fasting insulin level is associated with various constituents of the insulin resistance syndrome, such as obesity, dyslipidemia, and increased serum glucose 3
- Fasting insulin level can be used to identify patients with the insulin resistance syndrome who are exposed to increased risk of coronary artery disease 3
- Measuring fasting insulin level, in addition to glucose level, can help detect insulin resistance in individuals with normal fasting glucose concentrations 5