Study shows daily glucose levels fluctuate more than we thought, challenging diabetes diagnosis (2024)

Study shows daily glucose levels fluctuate more than we thought, challenging diabetes diagnosis (1)By Vijay Kumar MalesuApr 11 2024Reviewed by Susha Cheriyedath, M.Sc.

In a recent study published in the journal Nature Medicine, researchers examined fasting glucose (FG) variability in nondiabetic adults using continuous glucose monitoring (CGM), assessing its impact on diabetes classification and its association with clinical measures.

Study shows daily glucose levels fluctuate more than we thought, challenging diabetes diagnosis (2)Study:Continuous glucose monitoring and intrapersonal variability in fasting glucose. Image Credit:Suriyawut Suriya/ Shutterstock


The global increase in prediabetes and diabetes poses significant health risks and financial burdens. Diagnosis primarily relies on elevated plasma fasting glucose (PFG), glycated hemoglobin (HbA1c) levels, the oral glucose tolerance test (OGTT), or random plasma glucose in symptomatic individuals. However, the OGTT is often bypassed due to its cost and inconvenience, leaving PFG and HbA1c as key diagnostic tools, especially for asymptomatic cases. Despite its diagnostic importance, the day-to-day variability of PFG in nondiabetic individuals remains underexplored, potentially leading to misdiagnosis. CGM devices, which measure interstitial glucose levels, offer improved accuracy over time and are now used independently or in hybrid closed-loop systems for insulin dosing. Further research is needed to develop CGM-based diagnostic criteria that accurately reflect the intrapersonal variability of FG levels and their clinical implications.

About the study

The present study analyzed data from the 10K study, focusing on individuals aged 40 to 70 years. At baseline, various measures, including lifestyle, nutritional habits, vital signs, and medical history were collected alongside specific tests such as blood tests, electrocardiography, and CGM using the FreeStyle Libre Pro Flash system for two weeks. This study included participants without a self-reported diagnosis of type 2 diabetes or related conditions who also engaged in active meal logging alongside their CGM data. Exclusion criteria were rigorous, including abnormal CGM readings and inadequate meal logging.

The research particularly emphasized FG measurements during morning hours, utilizing CGM data to observe intrapersonal variability and its potential impact on diabetes diagnosis. The methodology ensured a realistic emulation of fasting conditions, relying on at least 8 hours of no caloric intake prior to the measurement windows and rigorous meal logging criteria. A total of 8,315 individuals with 59,565 fasting morning windows were analyzed for FG variability and its correlation with various clinical measures, including anthropometry, vital signs, and sleep monitoring, among others. Sleep monitoring employed the Food and Drug Association (FDA)-approved WatchPAT-300 device, while detailed retinal imaging and other health metrics were carefully analyzed for associations with FG variability. Furthermore, the study applied statistical analyses to explore the relationship between FG variability and clinical measures, considering age and gender.

Study results

In analyzing FG measurements from 8,315 individuals across 59,565 morning windows, researchers delved into the details of FG variability and its implications for diabetes classification. The study participants, averaging 51.3 years, had a mean body mass index (BMI) of 25.92 ± 4.07 kg m−2. Data collection was rigorous, with morning FG measurements taken between 06:00 and 09:00, following a predefined minimum of 8 hours of fasting, although the actual mean fasting duration was over 10 hours. Notably, fasting duration showed no significant correlation with FG values.

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The study's methodology was thorough in calculating FG for each individual, ensuring valid morning windows through strict criteria, including active meal logging. This large-scale examination revealed an average FG value of 96.2 mg dl−1, which was observed to increase slightly with age, indicating a gradual rise in glucose levels over time. The analysis also highlighted considerable day-to-day variability in FG measurements within individuals, a finding that underscores the complex nature of glucose metabolism and its sensitivity to various factors.

In assessing the potential for misclassification of diabetes and prediabetes based on FG levels, the research unearthed significant variability. A notable portion of participants experienced shifts in their glycemic status classification throughout the study, emphasizing the limitations of relying on a single FG measurement for diagnosing diabetes. This variability, coupled with the narrow range defining normal and diabetic FG levels, suggests a need for refined diagnostic criteria to better accommodate individual glucose reading fluctuations.

The study also examined the clinical correlations of FG variability to various health indicators such as body composition, blood pressure, and liver function. Interestingly, FG variability showed significant associations with several clinical measures, highlighting its potential as a marker for metabolic health. Particularly, correlations with body composition and daily caloric intake suggest that FG variability might reflect broader metabolic processes beyond glucose regulation alone.


To summarize, this research analyzed FG data from 8,315 nondiabetic individuals using CGM, uncovering significant FG variability that challenges the reliability of current diabetes diagnostic criteria based on PFG. Initial classifications indicated most participants had normal FG levels, but further measurements suggested a substantial shift towards prediabetes, highlighting the risk of misclassification. The study demonstrated that increasing the number of FG tests could significantly reduce misdiagnosis. Additionally, it found meaningful associations between FG levels and various clinical measures within normal glucose ranges, suggesting the need for a better approach to diabetes diagnosis that considers the variability and dynamic nature of FG levels.

Journal reference:

Study shows daily glucose levels fluctuate more than we thought, challenging diabetes diagnosis (2024)


Should I worry about fasting glucose 103? ›

Fasting blood sugar test

In general: Less than 100 mg/dL (5.6 mmol/L ) is normal. 100 to 125 mg/dL (5.6 to 6.9 mmol/L ) is diagnosed as prediabetes. 126 mg/dL (7.0 mmol/L ) or higher on two separate tests is diagnosed as diabetes.

Should I test my blood sugar if I'm not diabetic? ›

For healthy people, blood sugar testing is typically recommended every three years or so; if prediabetes is diagnosed, repeat testing is recommended more often, at least yearly. CGM might allow earlier diagnosis of prediabetes or diabetes.

What are the three criteria for diagnosing diabetes? ›

  • A1C ≥6.5%. ...
  • FPG ≥126 mg/dL (7 mmol/L). ...
  • 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during an OGTT. ...
  • In a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose ≥200 mg/dL (11.1 mmol/L).

Why is my fasting blood sugar over 200? ›

High Blood Glucose: Hyperglycemia

It happens when your blood glucose level is around 200 mg/dL or higher. Hyperglycemia can happen if you miss taking your diabetes medications, eat too much or do not get enough exercise. Sometimes, the medications you take for other problems cause high blood glucose.

Why is my blood sugar high in the morning but normal all day? ›

The cause of the dawn phenomenon isn't clear. Some researchers believe the overnight release of certain hormones that happens naturally increases insulin resistance. That causes blood sugar to rise. The hormones are called counter-regulatory hormones because they have an effect that opposes the effect of insulin.

How high can your blood sugar get if you don t have diabetes? ›

You can have high blood sugar levels without diabetes, especially after eating sugary foods. A high glucose level is above 100 milligrams per deciliter (mg/dL) fasting for those without diabetes or 140 mg/dL within 2 hours of eating. High blood sugar isn't a condition that's limited to people with diabetes.

Can blood sugar be normal and still have diabetes? ›

Yes. In some people, a blood glucose test may show diabetes when an A1C test does not. The reverse can also occur—an A1C test may indicate diabetes even though a blood glucose test does not.

How many times a day should a type 2 diabetes check blood sugar? ›

Keep these factors in mind: Most people with type 2 diabetes only need to check their blood sugar once or twice a day. If your blood sugar level is under control, you may only need to check it a few times a week. You may test yourself when you wake up, before meals, and at bedtime.

What is the gold standard for diagnosing diabetes? ›

The gold standard diagnostic method for diabetes has previously been the measurement of either fasting blood glucose (FBG) or two-hour plasma glucose via an oral glucose tolerance test (OGTT). The diagnostic criteria for a patient to be considered diabetic using FBG or OGTT is: FBG ≥7.0 mmol/l, or.

Which is more accurate, fasting glucose or A1C? ›

Generally, FBS was a more accurate predictor for HbA1c compared with HbA1c as a predictor of FBS. Although the optimum cutoff point of HbA1c was >6.15%, its precision was comparable with the conventional cutoff point of >6%.

What is normal A1C by age? ›

A1C levels by age
Age groupAll respondentsWomen
20–39 years4.0–6.04.0–5.8
40–59 years4.1–6.24.1–6.1
≥ 60 years4.4–6.64.4–6.5
Nov 22, 2023

What two fruits should a diabetic avoid? ›

The worst fruits for people with diabetes include mango, jackfruit, banana, chikku and grapes. These fruits are high in sugar and low in fiber. These are considered the 5 worst fruits for people with diabetes. These fruits contain a lot of sugar.

How do you feel when your blood sugar is too high? ›

increased thirst and a dry mouth. needing to pee frequently. tiredness. blurred vision.

What are pre-diabetic feet? ›

Prediabetes Symptoms

“Some people with prediabetes may already have nerve damage, which can cause tingling or numbness in the feet and hands,” she notes. If you are at risk for prediabetes, your doctor may test your blood for sugar levels, or a blood sugar test might be part of your regular check-up.

What does it mean when your blood sugar is 103? ›

Blood glucose results would fall in the 100-125 mg/dL for the prediabetes range. A provider might also do another blood test, an A1C, which looks at the amount of glucose (sugar) stuck to blood. A1C results of 6.5% or higher would point to diabetes; 5.8-6.4% is categorized as prediabetes.

What is an alarming fasting sugar level? ›

In general, a blood sugar reading of more than 180 mg/dL or any reading above your target range is too high. A blood sugar reading of 300 mg/dL or more can be dangerous. If you have 2 readings in a row of 300 or more, call your doctor. What causes high blood sugar?

What is dangerously high fasting blood sugar? ›

Fasting hyperglycemia. This is blood sugar for people who have diabetes that's higher than 130 mg/dL (milligrams per deciliter) after not eating or drinking for at least 8 hours. If your fasting blood glucose is 100 mg/dL to 125 mg/dL, this means you have prediabetes. Postprandial or after-meal hyperglycemia.

What is a concerning fasting glucose level? ›

Fasting Blood Sugar Test

This measures your blood sugar after an overnight fast (not eating). A fasting blood sugar level of 99 mg/dL or lower is normal, 100 to 125 mg/dL indicates you have prediabetes, and 126 mg/dL or higher indicates you have diabetes.


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