Diagnosing Type 2 Diabetes early is vital for preventing complications, yet doctors often rely on standard blood tests that may not be equally accurate for everyone. A large new analysis of data from population-based studies across continents offers fresh insight into how best to detect this condition. The researchers examined over 276,203 adults who did not have a previously diagnosed diagnosis of diabetes. They compared two common blood markers: fasting plasma glucose and HbA1c, against the standard two-hour plasma glucose test used to confirm the disease.
The study found that fasting plasma glucose showed higher diagnostic accuracy than HbA1c. When fasting glucose was used, the optimal cutoff value was 6.3 mmol/L. At this level, the test correctly identified 73% of people with diabetes and correctly ruled out diabetes in 91% of those without it. In contrast, HbA1c showed lower diagnostic accuracy. Its optimal cutoff was 47 mmol/mol, which is roughly 6.5%. At this level, the test correctly identified only 62% of people with diabetes, though it still ruled out diabetes in 92% of healthy individuals.
The analysis also highlighted significant regional differences in how these tests perform. The best cutoff value for fasting glucose varied from 5.3 mmol/L in North America to 6.5 mmol/L in Asian countries. Similarly, the best cutoff for HbA1c ranged from 41 mmol/mol in Asian countries to 45 mmol/mol in North America. This suggests that a single global threshold might not fully reflect population-specific differences in how these markers work.
The researchers did not report any adverse events, serious adverse events, or issues with tolerability because this was a diagnostic accuracy study, not a treatment trial. The certainty of the evidence was rated as low. This means further high-quality studies are needed to refine diagnostic performance and examine factors influencing accuracy. People should not overstate the reliability of HbA1c compared to fasting glucose based on this single analysis.
For patients right now, these results suggest that fasting glucose is a more reliable diagnostic marker than HbA1c for detecting Type 2 Diabetes. However, doctors will likely continue to use both tests and clinical judgment. Uniform global thresholds may not be the best approach for every population. Patients should discuss their specific test results with their healthcare provider to understand what the numbers mean for their individual health.