Introduction.
Diabetes is a chronic condition of "high blood sugar" in our bodies. However, there have been historical changes in the criteria used to determine at what stage the diagnosis of "diabetes" is made. In recent years, diagnostic criteria using not only blood glucose levels but also HbA1c (hemoglobin A1c) have been adopted internationally and reflected in Japanese practice guidelines (e.g., Diabetes Care Guidelines 2024).
This article provides an easy-to-understand explanation of the current diagnostic criteria, their evolution, and points to note. It also introduces the diagnosis and evaluation system at Ikejiri-Ohashi Sera Clinic.
1. current diagnostic criteria - Japanese and international
Japan (Japan Diabetes Society, Clinical Practice Guidelines 2024)
In Japan, the 2024 edition of the guidelines defines diabetes as one of the following
- Fasting blood glucose ≥ 126 mg/dL
- Blood glucose level ≥ 200 mg/dL after 2 hours of oral glucose tolerance test (OGTT)
- HbA1c ≥ 6.5% (but should be used in conjunction with other blood glucose criteria)
- Blood glucose at any time (blood glucose measured at any time) ≥ 200 mg/dL + symptoms of hyperglycemia
However, it is stipulated that in cases with typical hyperglycemia symptoms, a single test can be considered definitive. The need for repeat testing depends on the case.
International/U.S. standards (ADA, etc.)
Internationally, the following criteria are commonly used
- Fasting plasma glucose (FPG) ≥ 126 mg/dL
- OGTT 2-hour value ≥ 200 mg/dL
- HbA1c ≥ 6.5 %
- Blood glucose at any time ≥ 200 mg/dL + hyperglycemic symptoms
These criteria are for the most part consistent with the Japanese standards. However, there are differences among countries and guidelines in whether HbA1c is formally incorporated into the diagnostic criteria and how it is utilized.
2. evolution and recent review of diagnostic criteria
Introduction of HbA1c
In the past, the mainstream criteria for diagnosis were based on blood glucose levels alone, but since 2009, following international discussions, there has been a growing trend to add HbA1c ≥ 6.5% as one of the diagnostic criteria.
With this introduction, it is now possible to reflect average blood glucose, which is less susceptible to temporal blood glucose fluctuations.
Review of normal range of fasting blood glucose
In Japan, there used to be a concept that the upper limit of fasting blood glucose was 110 mg/dL, but this was later revised to set the “normal high” range at 100-109 mg/dL.
Reorganization of Reinspection Requirements
In the past, "two or more positive tests" were often required, but nowadays, the standard is to confirm the results after only one positive test if a high blood glucose level with typical symptoms is confirmed.
Recent adjustments
The latest guidelines emphasize the importance of combining HbA1c with other glycemic criteria. In other words, neither blood glucose nor HbA1c alone is sufficient.
It also states to be aware of factors that can affect HbA1c, such as fluctuations in measurement accuracy, anemia, abnormal renal function, and blood transfusions.
3. points and limitations to note when diagnosing
- Factors affecting HbA1c: Anemia, impaired renal function, and abnormal red blood cell lifespan can lead to misinterpretation of HbA1c.
- Environmental dependence of fasting and OGTT testing: dietary restrictive status and test preparation influence the results.
- Borderline (pre-diabetes) treatment: Fasting blood glucose 100-125 mg/dL and HbA1c 5.7-6.4 % are treated as pre-diabetes (prediabetes) and are considered at high risk for future development.
- Hyperglycemia without typical symptoms: Many cases test positive without symptoms and are at risk of being missed.
Diagnosis and evaluation system at Ikejiri-Ohashi Sera Clinic
The hospital takes the following actions based on the diagnostic criteria
- Combination of multiple measurement methods
Fasting blood glucose, blood glucose at any time, HbA1c, and if necessary, OGTT are combined for determination. - Timing and determination of re-inspection
The policy is to make an immediate diagnosis when high blood glucose levels with typical symptoms are confirmed, while asymptomatic cases are retested to confirm the diagnosis. - Complication Risk Assessment
From the time of diagnosis, a combination of fundus examination, ABI, carotid echocardiography, and Holter electrocardiography are used for early evaluation of vascular, cardiac, and renal effects. - Integration with initial response after diagnosis
From the time of diagnosis, lifestyle modification, exercise therapy, and nutritional guidance are provided in conjunction. If necessary, a decision is made to begin drug therapy immediately. - Follow-up and Monitoring
Regularly track blood glucose and HbA1c to check for fluctuations, and begin management with complication prevention in mind immediately after diagnosis.
summary
- Current diagnostic criteria are determined using fasting blood glucose, OGTT, anytime blood glucose, and HbA1c. If the patient has typical symptoms, the diagnosis can be confirmed at the first time.
- In the past, there have been transitions such as the non-introduction of HbA1c and the revision of the fasting blood glucose limit, and recently the emphasis has been on "combining multiple criteria.
- In some cases, HbA1c cannot be determined in isolation because of the factors that influence it.
- We have a system in place to make precise determinations based on multiple tests, and to evaluate complications and initiate lifestyle improvement at the same time as diagnosis.
References
- The Japan Diabetes Society. Guidelines for Diabetes Care 2024.
- The Japan Diabetes Society “Guideline for Diagnosis” PDF
- Diabetes Standard Medical Practice Manual 2025 (describing diagnostic criteria)
- ADA “Diagnosis and Classification of Diabetes.”
- New diabetes diagnosis criteria including HbA1c (MHLW data)
Diabetes Series - Related Article List
1. Know the basics of diabetes
- What is Diabetes - Why does blood sugar rise? Causes and Mechanisms Explained
Introduces the root causes of diabetes, including "insulin resistance," "heredity," and "lifestyle," which are all related to the development of diabetes, in an easy-to-understand manner. - Early Symptoms of Diabetes - Don't Miss the Early Detection Signs
Early signs that are difficult to recognize, such as thirst, polyuria, and weight loss, are carefully explained. - Diagnostic criteria for diabetes - Difference between HbA1c, blood glucose and OGTT and latest criteria
It summarizes the numerical values used for diagnosis and the key points of the recently revised diagnostic criteria. - Diabetes Testing - Comprehensive evaluation of blood, urine, and even complications
Introduction to the comprehensive examination system available at the Ikejiri-Ohashi Sera Clinic, including fundus examination, ABI, and carotid artery echocardiography.
2. Treatment and lifestyle modification
- Diabetes Treatment - Protecting Blood Sugar and Blood Vessels with Diet, Exercise, and Medication
Explains treatment strategies to "prevent complications" rather than "lower the numbers. - Diabetes Diet - Control Blood Sugar Effortlessly with Locavore
A practical diet that emphasizes how to eat, not what not to eat. - Diabetes and Exercise - Muscle is Medicine! The Science of Aerobic x Muscle Training
The benefits of exercise to directly lower blood sugar and how to create an easy to follow exercise routine. - Drug Therapy for Diabetes Mellitus - Latest Treatment Policies and Multi-Drug Approaches
The characteristics of DPP-4 inhibitors, SGLT2 inhibitors, and GLP-1 agonists are compared, and the latest treatment trends are presented.
3. To prevent complications
- Complications of diabetes - Complication measures to remember with "shimeji" and "enoki" mushrooms
The six major complications of neuropathy, retinopathy, nephropathy, gangrene, stroke, and cardiac disease are explained together. - Neuropathy due to diabetes - Mechanisms and countermeasures for numbness and pain in hands and feet
Early signs of peripheral neuropathy and ways to improve life that should be done early. - Diabetes and Renal Dysfunction - Importance of Urine Albumin Testing and Habits to Protect
Practical approaches to reduce the burden on the kidneys and prevent dialysis. - Diabetes and Eye Disease - Causes of Blurred Vision and Early Detection of Retinopathy
Explains how fundus camera examinations work and the risks of neglect.
4. Prevention and early intervention
- Prevention of Diabetes - Reduce blood sugar waves and make your body less prone to diabetes.
Introduces diet, exercise, and sleep regimens to "get in shape before it happens," rather than "fix it after it happens. - Characteristics and constitution of people prone to diabetes - Self-check that you can do now
Early intervention is recommended by sorting out the risk of developing the disease, including heredity, fatty liver, and lack of exercise.
5. Our features and support system
- Lifestyle-related disease treatment at Ikejiri-Ohashi Sera Clinic - Cross-cutting management of diabetes, MASLD, hypertension and dyslipidemia
Includes a comprehensive evaluation system including physician supervised exercise therapy, locavore diet support, fundus, ABI, and carotid artery echocardiography.