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I've been a competing athlete, mostly in endurance sports for nearly 45 years now. As part of military and other physicals, I have had blood glucose levels come back several times with high levels, and follow up Fasting Glucose Tolerance Tests come back as negative. In one of my most recent blood panels (for a medical study group) came back with HbA1c levels that indicated I was prediabetic, but again, follow up studies were negative.

Recently I read a blog post discussing this study, which indicated that highly trained endurance athletes (In this case, a cohort of 47 professional and 72 elite male cyclists, compared to 58 sedentary donors) trended higher HbA1c levels than the sedentary group.

I have also read that many of the blood glucose levels were established using diabetic patients, so does that mean that the levels are not valid for me since I am a lifelong endurance athlete? Or is this something that I should just keep following up with potentially unnecessary tests?

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When you say

In one of my most recent blood panels (for a medical study group) came back with HbA1c levels that indicated I was prediabetic, but again, follow up studies were negative.

What was the HbA1C level, and what follow-up study was negative?

In the Lippi study, HbA1c values between sedentary individuals and professional cyclists were 5.2 +/- 0.3% versus 5.4 +/- 0.2% respectively. That's really fairly marginal. Normal levels are below 5.7 percent.

HbA1C levels are indeed valid concerns for athletes, as valid as for anyone else. The risk of heart disease, however, is lower in this group in spite of the elevated A1C because of fitness levels.

Glucose molecules don't respect elite cyclists more than couch potatoes. End-organ damage (through glycosylation) is the primary concern here. Your kidneys and eyes (among other things) aren't helped by your exercise, but they are damaged by diabetes.

Type 2 diabetes Mayo Clinic

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    You have a good point here. High glucose level is the bad guy, not the possible aetiology, basically. I believe that JohnP is at the lowest risk group for any diabetes related disease due endurance sports which are good for general health. Nevertheless I would not totally ignore the sporadically elevated values, but neither I think that repetitive tests are useful for rest of the life. – arkiaamu Aug 31 '15 at 19:05
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    You need a reference to show that fitness levels protect against heart disease. Cardiovascular health does not correlate with vascular intimal health. – Graham Chiu Apr 15 '16 at 4:12
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    eurheartj.oxfordjournals.org/content/29/15/1903.full "Conventional cardiovascular risk stratification underestimates the CAC burden in presumably healthy marathon runners. As CAC burden and frequent marathon running seem to correlate with subclinical myocardial damage, an increased awareness of a potentially higher than anticipated coronary risk is warranted." – Graham Chiu Apr 15 '16 at 4:48
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Yes, high blood sugar levels can cause damage in the body---but it is SUSTAINED high blood sugar levels that are dangerous. Here is another interesting article on A1c and athletes: http://fitafter40vancouver.blogspot.com/2010/12/hba1c-and-athletes.html

Athletes may have short bursts of higher glucose in their blood stream after exercise and not prolonged high levels.

I, too, am an endurance athlete (ultra-marathon runner) who tends to have borderline high A1c results. My last results was 5.7.

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    Thank you for your experience! The post you reference is the same one that I also linked, that was what prompted my original question, as well as the tendency to produce false positives on glucose tests. – JohnP Oct 8 '15 at 16:31
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The expert opinion of the study author Lippi appears now to be just the opposite from the possible conclusion drawn in the question:

Hyperglycemia has been the leading diagnostic criterion for diagnosing diabetes since the development of blood glucose assays 100 years ago (25). The ADA has recently advocated using HbA1c for the diagnosis of diabetes and the identification of those at high-risk of developing diabetes. However, at present no other organizations or scientific societies, including the IFCC and the European Federation of Clinical Chemistry (EFCC), have officially endorsed this recommendation. Although a clinical role might exist for screening (i.e., by using a HbA1c cut-off between 6.5% and 7.0%), it seems premature to conclude that HbA1c measurement, at least alone, might be sufficiently accurate to allow wide-spread implementation for the diagnosis of diabetes. At present, its diagnostic role should be limited to those patients with no comorbidities or patho-physiological conditions that might reduce the diagnostic efficiency of this test (Table 2). Whether the old dogma of HbA1c testing for monitoring overall glycemic exposure will translate into a valuable tool for the diagnosis of diabetes, only the future and analysis of its cost effectiveness will determine this role. The article from the GLAD Working Group published in this issue of Clinical Chemistry and Laboratory Medicine, which is aimed at promoting a coordinated plan for implementing the standardization of HbA1c measurement in Italy, represents a foremost contribution for further investigations on this topic.

Giuseppe Lippi & Giovanni Targher: "Glycated hemoglobin (HbA1c): old dogmas, a new perspective?", Clin Chem Lab Med 2010;48(5):609–614. DOI:10.1515/CCLM.2010.144

And very recently

The results of our study, which is based on a larger sample size than previous investigations, show that the concentration of plasma glucose is significantly decreased from 3 to 24hours after endurance running. Unlike plasma glucose, HbA1c values were almost unchanged up to 24hours after a half-marathon run, thus suggesting that this parameter may be more reliable than FPG or RPG for diagnosing diabetes in physically active subjects, regularly engaged in recreational or competitive endurance activity.

Giuseppe Lippi et al.: "Challenges of diagnosing diabetes in endurance athletes", J Clin Pathol 2018;71:944–945. doi:10.1136/jclinpath-2018-205043

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