The Hidden Dangers of Relying Solely on HbA1c in Diabetes Care
- Mohammed A Rashad
- 1 day ago
- 5 min read
Every diabetes review brings a familiar number into focus: the HbA1c. For years, this single figure has shaped treatment plans, guided medication changes, and reassured both clinicians and patients that glucose control is on track. But what if the story behind that number is more complicated than it seems? Beneath its reassuring simplicity, HbA1c can sometimes mask hidden risks, leading to decisions that may not always serve the patient’s best interests.
Recent studies reveal that up to one in five people with diabetes may have misleading HbA1c results due to factors like anaemia, kidney disease, or rapid changes in blood sugar. For the busy healthcare professional, this means that relying solely on HbA1c could result in missed diagnoses, inappropriate therapy adjustments, or even harm.
In this blog, The Medicines Management Team uncovers the hidden dangers of depending on HbA1c alone and shares practical strategies to ensure safer, more personalised diabetes care.
Key Takeaways:
HbA1c and Its Role in Diabetes Management
HbA1c, or glycated haemoglobin, has become a cornerstone in diabetes care. This blood test reflects the average blood glucose level over the previous two to three months, offering a convenient snapshot of long-term glycaemic control. Its widespread adoption is no accident: HbA1c is easy to measure, does not require fasting, and is strongly linked to the risk of diabetes complications such as retinopathy, nephropathy, and cardiovascular disease.
For most people living with diabetes, regular HbA1c monitoring helps guide treatment decisions, track progress, and set realistic goals. However, while HbA1c is invaluable, it is not infallible. There are important situations where this trusted marker can mislead, sometimes with serious consequences.
When HbA1c Results Can Be Misleading
1. Altered Red Cell Turnover
HbA1c measures the percentage of haemoglobin that has glucose attached to it. Anything that affects the lifespan or turnover of red blood cells can distort the result.
Key scenarios include:
Anaemia: Conditions like haemolytic anaemia, where red blood cells are destroyed faster than normal, can falsely lower HbA1c. Conversely, iron deficiency anaemia may increase HbA1c, even if glucose control is unchanged.
Recent Blood Transfusion: Transfused red cells may have a different glycation profile, leading to inaccurate readings.
Erythropoietin (EPO) Therapy: Used in chronic kidney disease, EPO stimulates new red cell production, which can lower HbA1c independently of glucose levels.
Haemoglobinopathies: Genetic conditions such as sickle cell disease or thalassaemia can interfere with the accuracy of many HbA1c assays.
2. Haemoglobin Variants
Not all haemoglobin is the same. Variants in haemoglobin structure, common in certain ethnic groups, can affect how HbA1c is measured. Some laboratory methods may not detect these variants, while others may give falsely high or low results. It is crucial to know your patient’s background and consider alternative tests if a haemoglobinopathy is suspected.
3. Pregnancy
Pregnancy brings unique challenges to diabetes monitoring. Increased red cell turnover, changes in iron status, and physiological shifts mean that HbA1c is less reliable for both diagnosis and monitoring. For pregnant women, especially those with gestational diabetes, capillary blood glucose profiles or continuous glucose monitoring (CGM) are preferred.
4. Chronic Kidney Disease (CKD) and End-Stage Renal Disease (ESRD)
People with advanced kidney disease often have anaemia, altered red cell lifespan, and may be on EPO therapy. These factors can all skew HbA1c results. In CKD and ESRD, HbA1c may underestimate or overestimate true glycaemic control, making it a less reliable guide for therapy adjustments.
5. Rapid Glycaemic Changes
HbA1c reflects an average, not the highs and lows. If a patient’s glucose control has changed rapidly—due to new medication, illness, or lifestyle changes—HbA1c will lag behind. This delay can mask recent improvements or deteriorations, leading to inappropriate clinical decisions.
6. High-Dose Steroid Therapy
Steroids can cause significant, rapid increases in blood glucose. However, because HbA1c averages glucose over several weeks, it may not reflect these acute changes. Relying on HbA1c alone in patients on steroids can result in missed hyperglycaemia and delayed treatment.
When to Question the HbA1c
It is vital to recognise when HbA1c may not be telling the whole story. Consider the following red flags:
Mismatch between HbA1c and capillary glucose readings: If a patient’s home glucose monitoring or CGM data does not align with their HbA1c, investigate further.
Unexpectedly low or high HbA1c in the context of known risk factors: For example, a patient with advanced CKD and anaemia presenting with a surprisingly low HbA1c.
Recent changes in health status: New anaemia, recent transfusion, or pregnancy should prompt caution in interpreting HbA1c.
Alternatives to HbA1c: What Are the Options?
When HbA1c is unreliable, alternative markers and monitoring methods can provide a clearer picture.
Fructosamine and Glycated Albumin
Fructosamine measures glycated serum proteins, reflecting average glucose over the past 2–3 weeks. It is not affected by red cell turnover but can be influenced by changes in protein levels (e.g., nephrotic syndrome, liver disease).
Glycated albumin is similar, offering a short-term view of glycaemic control. It is particularly useful in pregnancy, haemoglobinopathies, and situations with rapid glucose changes.
Continuous Glucose Monitoring (CGM) and Capillary Profiles
CGM provides real-time data on glucose trends, capturing fluctuations that HbA1c misses. It is especially valuable in pregnancy, steroid therapy, and for patients with hypoglycaemia unawareness.
Capillary blood glucose profiles (finger-prick testing) remain a practical option, especially when CGM is not available. Structured testing—such as pre- and post-meal readings—can help identify patterns and guide therapy.
Practical Tips for Effective Diabetes Care
To ensure safe and effective diabetes care, consider these best practices:
Always interpret HbA1c in context: Review recent full blood count, renal function, and iron studies before making therapy changes.
Be alert to clinical scenarios where HbA1c may mislead: Pregnancy, CKD, anaemia, haemoglobinopathies, and recent transfusion all warrant caution.
Use alternative markers when needed: Fructosamine, glycated albumin, CGM, and capillary profiles can provide more accurate information in specific situations.
Communicate with the wider multidisciplinary team (MDT): If results are unexpected or discordant, discuss with colleagues and document your rationale for any changes.
Educate patients: Help them understand why different tests may be needed and the importance of regular monitoring.
Conclusion
HbA1c remains a powerful ally in diabetes management, but it is not a one-size-fits-all solution. By understanding its limitations and knowing when to use alternative monitoring strategies, healthcare professionals can provide safer, more personalised care.
The Medicines Management Team encourages all clinicians to look beyond the numbers, interpret results in context, and always put patient safety at the heart of diabetes care.
FAQs
Can HbA1c be used to diagnose diabetes in all patients?
No, HbA1c is not suitable for diagnosing diabetes in certain groups, such as pregnant women, people with haemoglobinopathies, or those with significant anaemia. In these cases, alternative tests like fasting plasma glucose or oral glucose tolerance tests are recommended.
How often should HbA1c be checked in stable patients with diabetes?
For most stable patients, HbA1c should be measured every 3 to 6 months. However, the frequency may be increased if there are changes in therapy, unstable glycaemic control, or new health issues.
What should I do if a patient’s HbA1c does not match their home glucose readings?
If there is a mismatch, review for factors that could affect HbA1c accuracy, such as anaemia or recent transfusion, and consider using alternative monitoring methods like fructosamine or CGM to get a clearer picture.
Are there any risks to using alternative markers like fructosamine?
Fructosamine and glycated albumin can be affected by conditions that alter protein levels, such as liver disease or nephrotic syndrome. Always interpret these results in the context of the patient’s overall health.
Why is continuous glucose monitoring (CGM) becoming more popular?
CGM provides real-time data and trends, helping to identify glucose fluctuations and patterns that HbA1c cannot capture. This can lead to more personalised and effective diabetes management, especially in complex cases.
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