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Does diabetes show up in routine blood work?

Routine blood work refers to common blood tests that doctors order regularly to assess a patient’s overall health and screen for any potential issues. Blood work provides valuable information about how well different organs are functioning and can sometimes detect health problems before symptoms appear. Diabetes is one condition that may be uncovered during routine blood work, even if the patient has no symptoms of diabetes at the time of testing. This article will explore how routine blood tests may reveal diabetes or a prediabetes condition.

What is included in routine blood work?

Routine blood work typically includes a fasting blood glucose test and a hemoglobin A1C test, both of which can indicate diabetes or prediabetes.

Fasting blood glucose

A fasting blood glucose test measures the amount of glucose (sugar) in the blood after fasting for 8-12 hours. This test is usually done first thing in the morning before eating or drinking anything besides water. Normal fasting blood glucose levels are less than 100 mg/dL.

A fasting blood glucose level between 100-125 mg/dL indicates prediabetes. This means the blood sugar is elevated but not high enough for a diagnosis of diabetes. Without lifestyle changes to lower blood sugar, prediabetes is likely to become type 2 diabetes within 10 years.

A fasting blood glucose level of 126 mg/dL or higher indicates diabetes. This is because a fasting blood glucose at or above 126 mg/dL reaches the threshold for a diagnosis of diabetes.

Hemoglobin A1C

The hemoglobin A1C test measures the average blood sugar over the past 2-3 months. It specifically looks at what percentage of hemoglobin proteins in the blood have glucose molecules attached to them. The higher the blood sugar, the more hemoglobin becomes glycosylated.

A normal A1C is below 5.7%. An A1C between 5.7-6.4% indicates prediabetes. An A1C of 6.5% or above means diabetes.

Can routine blood work detect prediabetes or undiagnosed diabetes?

Yes, the fasting blood glucose and A1C tests that are part of routine blood work can detect prediabetes or undiagnosed diabetes. Here’s how:

– The fasting blood glucose test can uncover higher-than-normal fasting blood sugar levels, indicating prediabetes or potentially undiagnosed diabetes if blood sugar is very high.

– The A1C test reflects average blood sugar over 2-3 months, so it can detect persistently elevated blood sugar even if fasting blood sugar alone is normal. An elevated A1C can reveal prediabetes or diabetes that is being missed through fasting blood glucose testing alone.

– People with prediabetes or undiagnosed diabetes often have no symptoms early on, so routine blood work may be the first indication that blood sugar is on the rise. Without routine screening, prediabetes or diabetes can be missed for years until complications appear.

Who should be screened for diabetes with blood work?

Health experts recommend routine screening for prediabetes and type 2 diabetes in the following individuals:

Adults over age 45

The risk of diabetes increases with age, so adults over 45 should have blood glucose and A1C checked at least every 3 years. More frequent screening may be recommended if BMI is 25 or higher.

Overweight or obese adults

Anyone with a BMI of 25 or higher has an increased risk for developing type 2 diabetes and should be screened.

BMI Weight Status
Below 18.5 Underweight
18.5-24.9 Healthy Weight
25-29.9 Overweight
30 or higher Obese

Those with prediabetes

People diagnosed with prediabetes through prior blood work should have their fasting glucose and A1C rechecked at least yearly. More frequent monitoring will allow early detection of progression to diabetes.

Women with a history of gestational diabetes

Women who develop gestational diabetes during pregnancy are at very high risk for developing type 2 diabetes later on. Annual screening with blood glucose and A1C tests is recommended going forward.

Individuals with risk factors for diabetes

Testing at least every 3 years is also advised for those with the following diabetes risk factors:

– Family history – Having a parent, brother, or sister with diabetes increases risk.
– Inactivity – Exercising less than 3 times per week.
– High blood pressure – Systolic pressure 130+ or diastolic 80+.
– Abnormal cholesterol – HDL under 35 mg/dL or triglycerides over 250 mg/dL.
– Polycystic ovarian syndrome
– Non-alcoholic fatty liver disease
– Sleep apnea
– Depression

Screening should start at age 35 if multiple risk factors are present.

What if blood work shows prediabetes or diabetes?

If routine blood work reveals elevated fasting blood glucose or A1C in the prediabetes or diabetes range, your doctor will likely order a repeat test on a different day to confirm the diagnosis. Follow up oral glucose tolerance testing may also be recommended.

If diabetes or prediabetes is confirmed, your doctor can help create a treatment plan to manage it. This will include healthy lifestyle changes such as:

– Losing excess weight through diet and exercise. Even a 5-10% weight loss can help normalize blood sugar.
– Starting a regular exercise routine of 150 minutes per week.
– Following a “diabetes diet” focused on lean proteins, high fiber carbohydrates, healthy fats, and micronutrients.
– Quitting smoking and limiting alcohol intake.
– Managing stress through meditation, yoga, etc.

Your doctor will also determine if diabetes medication or insulin injections could help normalize your blood sugar levels. Controlling blood sugar is key to preventing diabetes complications like heart disease, nerve damage, kidney disease, vision loss, and infections.

While receiving a diabetes or prediabetes diagnosis can be concerning, catching it early through routine blood work allows prompt treatment to preserve health and quality of life. Routine screening and blood glucose monitoring should become part of your regular preventive healthcare.

Can blood work miss a diabetes or prediabetes diagnosis?

Although blood glucose and A1C testing are reliable screening tools, it’s possible in some cases for routine blood work to miss diagnosing diabetes or prediabetes. Reasons this can happen include:

– Normal blood glucose during fasting – Some people with diabetes can maintain normal fasting blood sugar levels but experience spikes after meals. This can escape detection on a fasting blood glucose test alone.

– Normal A1C in early diabetes – The A1C may still be normal during the first months after diabetes develops. It takes 2-3 months to reflect new elevations in blood sugar.

– Testing done during illness – Blood sugar levels can temporarily go up or down during acute or chronic illness, leading to inaccurate test results.

– Improper test timing – Eating shortly before a fasting blood glucose test or having an unusually high-carb diet around the time of A1C can skew results.

– Human errors – Mistakes in sample labeling or test analysis can provide incorrect results.

– Individual variations in red blood cell turnover – Since A1C attaches to red blood cells, conditions affecting red blood cell lifespan may alter expected results.

If diabetes or prediabetes is strongly suspected based on risk factors and symptoms, your doctor may re-check blood work multiple times or order additional definitive testing like an oral glucose tolerance test. Diabetes requires at least two positive test results for diagnosis.

What are the symptoms of undiagnosed diabetes and prediabetes?

Diabetes and prediabetes often have no obvious symptoms in the early stages, which is why screening blood work is so important. Mild or vague symptoms that may indicate early diabetes or prediabetes include:

– Increased thirst and frequent urination – High blood sugar leads to excess urine production and volume depletion.
– Fatigue – Cells starved of glucose due to insulin resistance may leave you feeling tired and run down.
– Blurred vision – Fluctuating blood sugar levels can cause the lens of the eye to swell temporarily.
– Slow healing cuts/bruises – High blood sugar impairs immune function and wound healing.
– Recurrent infections – Weakened immunity due to diabetes allows more frequent infections.
– Tingling hands or feet – Nerve damage from diabetes can begin with numbness or pain in the extremities.

Once diabetes has progressed, more obvious symptoms like unexplained weight loss, fruity breath odor, and extremely heavy thirst/urination become noticeable. If you have any puzzling symptoms, discussing them with your doctor and requesting blood work can determine if diabetes or prediabetes could be the reason.


Routine fasting glucose and A1C blood tests are capable of uncovering elevated blood sugar levels before type 2 diabetes causes any symptoms. They provide an opportunity to detect prediabetes or undiagnosed diabetes through screening people at increased risk. Diabetes caught in its early stages affords the best chance to improve management through lifestyle interventions and medication and avoid devastating complications. Although false negative test results are possible, blood work remains critical for successful diabetes prevention and early treatment.