Diabetes: which tests to request and when glycemia meets diagnostic criteria (HbA1c, fasting glucose, OGTT)

In dentistry, the goal is screening and risk stratification: integrate HbA1c into periodontal planning and refer for medical evaluation when appropriate.

Persistent gingival bleeding, difficult-to-control periodontitis, or delayed healing may signal a relevant systemic modifier: glycemic control. Dentists do not establish a medical diagnosis of diabetes; however, they can — and often should — suspect, counsel, and refer.

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Laboratory thresholds commonly used in clinical practice

• Fasting plasma glucose ≥ 126 mg/dL

• HbA1c ≥ 6.5%

• OGTT (2 h after 75 g) ≥ 200 mg/dL

• Random plasma glucose ≥ 200 mg/dL with classic symptoms(AMERICAN DIABETES ASSOCIATION, s.d.; WORLD HEALTH ORGANIZATION, s.d.).

➡️ In many cases, confirmation with repeat testing is recommended based on clinical judgment and medical evaluation.

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Which test is most useful in periodontal practice?

In dental settings, HbA1c is often the most practical marker because it reflects average glycemia over recent weeks/months and is widely used in studies assessing oral outcomes in diabetes (PRESHAW, 2013; CHEE et al., 2025).

✅ Practical approach

• Known diabetes: document a recent HbA1c and the current medication list (CHEE et al., 2025).

• No diagnosis, but suspicion/risk: recommend medical evaluation and suggest HbA1c + fasting glucose as initial screening (AMERICAN DIABETES ASSOCIATION, s.d.).

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When should dentists “raise the flag”?

• frequent gingival bleeding and recurrent inflammation;

• deep/recurrent periodontal pockets;

• persistent halitosis;

• repeated infections;

• delayed post-procedure healing;

• metabolic risk factors (family history, weight gain, sedentary lifestyle, etc.).

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Conclusion

Diabetes is a periodontal risk modifier, influencing inflammation, healing, and treatment response (PRESHAW, 2013; SCHLIEPHAKE, 2022).

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Referências

AMERICAN DIABETES ASSOCIATION. Standards of Medical Care in Diabetes. [s.l.], [s.d.].

CHEE, H. K. et al. Long-Term Effect of Periodontal Therapy on HbA1c Changes in Type 2 Diabetes. Journal of Dental Research, v. 105, n. 1, p. 67–76, 2026.

PRESHAW, P. M. Diabetes and periodontitis: what’s it all about? Practical Diabetes, 2013.

SCHLIEPHAKE, H. The role of systemic diseases and local conditions as risk factors. Periodontology 2000, v. 88, p. 36–51,

2022.WORLD HEALTH ORGANIZATION. Diabetes diagnosis and management resources. [s.l.], [s.d.].