Otherindependent cross-checkabstract checked★ key study I-DIAB-106 in-depth review
HbA1c reflects average blood sugar
Translating the A1C assay into estimated average glucose values.
Overview
Nathan DM et al.. Diabetes Care 2008 · PMID 18540046 · DOI 10.2337/dc08-0545
In 507 people with about 2,700 glucose readings each, HbA1c closely matched the 3-month average blood sugar.
Does the study support the specific claim? No · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Link HbA1c to average glucose.
- How was the study done?
Observational method study.
- How many people, animals or samples were studied?
507 people.
- What was actually found?
eAG = 28.7 x A1C - 46.7; R2 0.84.
- How large was the observed effect?
HbA1c 7% = about 154 mg/dL.
- What do the results mean in everyday life?
HbA1c is a reliable average-sugar measure for most people.
- What are the study's limitations?
Some individuals deviate.
- What does it say about Elawady's specific claim?
Contradicts 'HbA1c is a lie'.
- Do the results apply to Germany and Europe?
Used in Europe.
- What can explicitly not be concluded from this study?
Cannot replace glucose checks in anaemia or haemoglobin disorders.
Scientific in-depth review
1. Full reference
- Authors
- Nathan DM et al.
- Journal
- Diabetes Care
- Year
- 2008
- Identifier
- PMID 18540046 DOI 10.2337/dc08-0545
- Verification
- verified – PubMed efetch 2026-10-26; Crossref 2026-10-26
- Retracted
- no
- Corrections
ErratumIn Diabetes Care 2009;32(1):207 (not a retraction)
- Extent checked
- abstract only
- Conflicts of interest and funding
Non-US government support (record).
2. Research question
What is the mathematical relationship between HbA1c and average glucose?
3. Study design and population
- Study design
- Other – International multicentre observational method study (ADAG)
- Population
268 T1D, 159 T2D, 80 without diabetes
- Country
10 international centres
- Period
3 months per participant
- Sample size
507
- Inclusion and exclusion criteria
As in paper
4. Methods and endpoints
- Exposure / intervention
Average glucose from CGM and 7-point SMBG (~2,700 values per person)
- Comparator
Central-laboratory HbA1c
- Endpoints
Regression HbA1c-average glucose
- Statistical methods
Linear regression
5. Actual results
- Results
AG (mg/dl) = 28.7 x A1C - 46.7, R2 = 0.84, P<0.0001; regression did not differ by age, sex, diabetes type, race/ethnicity or smoking.
- Absolute risks
not reported
- Authors' conclusion
A1C can be expressed as estimated average glucose for most patients with T1D and T2D.
6. Strengths
- Dense glucose sampling
- International
7. Weaknesses
- Few people with haemoglobin variants/anaemia
- Industry support possible (not stated)
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- low
- Rationale
Method-comparison study.
9. Assessment of the statistical interpretation
R2 0.84: strong but not perfect; individual discordance exists (stats/C-DIAB-01_adag.py).
10. Relevance to the specific claim
HbA1c closely tracks measured average glucose; 'HbA1c is a lie' is false, although individual deviations exist.
11. Independent contrary findings
12. Transferability to Germany and Europe
Directly applicable; same biology and clinical standards in Europe.
13. Overall methodological judgement
Key validation evidence.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | low |
| Precision of results | high |
| Directness | direct |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |