The case of the unreliable HbA1c — Part Two

The 42-year-old man with type 1 diabetes described in my previous post had excellent glycemic control according to his finger stick glucose but a falsely high HbA1c due to iron deficiency anemia. He already had an extensive evaluation which failed to identify the cause.

He denied gastrointestinal symptoms on his initial review of systems questionnaire. I asked him again very specifically about diarrhea and abdominal bloating which he denied. But then I rephrased the question: “How many bowel movements do you have in a day?”

He replied that he had five to seven but explained: “I’ve been that way all my life, it’s normal for me.” He admitted to sometimes having to spend an entire day not far from the bathroom “after I ate something wrong.” These episodes occurred about once every week or two.

When I told him that I had a very good idea about what might be going on, he was not optimistic: “I’ve had this for years and no one else has figured out why.” However, his tissue transglutaminase IgA antibody was 120 (<20 units) confirming a diagnosis of celiac.

A misconception has been that celiac is uncommon. However, this is not correct. The incidence of celiac in the general population is about 1:200. In individuals with autoimmune endocrine disorders the incidence may be much higher. In type 1 diabetes, it is estimated that as many as 1:20 have evidence of celiac on antibody testing.

Celiac sprue is a disease of gastrointestinal malabsorption with systemic complications. Untreated celiac can result in iron deficiency and other micronutrient deficiencies. People with celiac may have low bone mass due to vitamin D and calcium malabsorption. Many individuals with celiac have been misdiagnosed with irritable bowel syndrome.

With gluten avoidance, his loose stools improved. We also discovered vitamin D deficiency, his 25-hydroxyvitamin D was only 8 ng/mL. After receiving a course of ergocalciferol, the chronic muscle pain attributed to “fibromyalgia” disappeared. The dietary transition has been challenging because before his diagnosis he enjoyed bread and cereal. Occasionally his symptoms return when he consumes food containing hidden gluten. However, at a follow-up visit he told me: “This is the best I’ve felt in years.”

I test for celiac in type 1 diabetes frequently, especially in those with iron deficiency anemia, vitamin D deficiency, low bone mass, vitamin B12 deficiency, loose stools, abdominal bloating or a diagnosis of “irritable bowel syndrome.” Of all of the antibody studies, tissue transglutaminase IgA is the most sensitive and specific. However, be aware that up to 5% to 7% of individuals with celiac may also have IgA deficiency rendering IgA-based antibody testing unreliable. The gold standard of small bowel biopsy is still useful but is not absolutely required in patients with positive antibodies in whom you have a high degree of suspicion.

If you are not testing for celiac in patients at risk, I encourage you to consider doing so.