Introduction

Imagine judging a movie based solely on its average IMDb rating - no context, no plot details, no idea how wildly different the audience's opinions are. Would you really get the full story? That’s exactly what happens when we rely solely on HbA1c to assess blood sugar control.

For decades, the HbA1c test has been considered the gold standard in diabetes care. It measures the average blood sugar over the past two to three months, a decent summary, sure, but one that often hides the nuances. As diabetes care becomes more personalized and precise, HbA1c is slowly losing its stronghold, and it’s time we talked about why.

Understanding the Limitations of HbA1c: What It Misses About Blood Sugar

Let’s start with what HbA1c doesn’t tell you:

• Daily highs and lows: HbA1c is an average, so a person with dangerous post-meal spikes and overnight crashes can still have a “normal” result.
  
  

• Glycemic variability: It doesn’t show how much your glucose levels fluctuate, and large swings are associated with more complications.
  
  

• Hypoglycemia frequency: You could have a healthy-looking HbA1c while experiencing frequent, dangerous lows.
  
  

• Time spent in a healthy range: Known as Time in Range (TIR), this metric is now being recognized as a more useful predictor of diabetes complications.
  
  

• Influence of other factors: Red blood cell lifespan, kidney function, and even ethnicity can skew your HbA1c result, making it unreliable for many people.

Here’s the problem: If you're averaging a rollercoaster ride of 250 mg/dL highs and 50 mg/dL lows, HbA1c might say you're doing fine, even though you're not.

A 2020 study in The Lancet Diabetes & Endocrinology highlighted that HbA1c can significantly misrepresent actual blood sugar control in people with high variability. In other words, two people with identical HbA1c levels can have vastly different day-to-day experiences, and risks.

Why Certain Medical Conditions Make HbA1c Unreliable

HbA1c reflects how much glucose has bonded to hemoglobin in your red blood cells. But if your red blood cells are turning over faster or slower than normal, the result can be misleading.

• Anemia (especially iron-deficiency anemia) or vitamin B12 deficiency can falsely elevate HbA1c due to longer red blood cell lifespan.
  
  

• Hemolytic anemia or blood loss may cause HbA1c to appear lower than actual blood glucose levels, since cells don’t live long enough to bind as much glucose.
  
  

• Chronic kidney disease (CKD) often interferes with red blood cell production and survival, making HbA1c less reliable in these patients.
  
  

• Hemoglobin variants (e.g., in people with sickle cell trait or thalassemia) may also interfere with lab methods used to measure HbA1c.

In these cases, relying on HbA1c can lead to under- or over-treatment. A 2020 analysis in The Lancet Diabetes & Endocrinology emphasized that HbA1c should be interpreted with caution in people with these conditions, and ideally, supported by additional metrics.

HbA1c vs. Continuous Glucose Monitoring: A More Complete Picture

Enter Continuous Glucose Monitoring (CGM),  a technology that has changed the landscape of diabetes care.

A CGM is a small wearable device that checks glucose levels every few minutes and provides:

• Real-time insights
  
  

• Daily patterns and trends
  
  

• Alerts for highs and lows
  
  

• Personalized feedback on how your body reacts to food, stress, and activity

Here’s a simple comparison:

A person might have an HbA1c of 7%, but their CGM shows that they’re only in the healthy range 40% of the time, a red flag that would otherwise go unnoticed.

This shift is backed by science. A study in The Journal of Clinical Endocrinology & Metabolism found that higher glucose variability is associated with oxidative stress and inflammation, both of which contribute to complications like cardiovascular disease.

Exploring Alternative Markers for Better Diabetes Management

As diabetes care evolves, so do the tools we use. Beyond HbA1c and CGM, here are some other markers gaining traction:

• Time in Range (TIR): The percentage of time your glucose stays within the healthy range (usually 70–180 mg/dL). Experts now suggest aiming for at least 70% TIR.
  
  

• Glycated Albumin and Fructosamine: These track short-term glucose control over 2-3 weeks. Helpful when HbA1c doesn’t align with actual symptoms.
  
  

• 1,5-Anhydroglucitol (1,5-AG): This drops when blood sugar spikes after meals, making it a great complement to HbA1c.
  
  

• Glucose Management Indicator (GMI): An estimate of what your HbA1c would be based on your recent CGM readings, more reflective of current realities.

These markers allow for a more holistic and actionable approach to diabetes management.

The Impact of Blood Sugar Variability: Why HbA1c Alone Isn’t Enough

Let’s be blunt, variability matters. Here’s why:

• High variability is linked to increased risk of complications, including eye damage, nerve damage, and heart disease.
  
  

• Even if the average looks okay, large glucose swings can lead to oxidative stress, a major factor in diabetes-related inflammation and cell damage.
  
  

• Managing variability can improve energy levels, mood, and quality of life, things that HbA1c can’t measure.