After two tests for diabetes inconsistent results come back

Dear Dr Roach: Iama 74-year-old Chinese man with controlled hypertension, and I’m currently taking a statin at 10 mg. I am puzzled and confused with my recent tests results. They show that my fasting plasma glucose is normal (5 mmol/L), while my HbA1c shows that I fall in the “prediabetic” category at 6.3% (45 mmol/L).

Why the inconsistency in results? Which of the two tests is more accurate to diagnose diabetes? My doctor wants me to do a glucose tolerance test to confirm the diagnosis, but I am not keen.

Over the past few years, I have only done fasting plasma glucose tests, which were always normal. I am thinking of repeating the A1c before doing the tolerance test, if necessary. — H.L.

Dear H.L.: The apparent inconsistency is explained by the time course of the two tests. A plasma glucose test is a snapshot of the blood sugar in a particular instant, and when a person is fasting, it is likely to be low until the diabetes is well-advanced.

The first problem in early diabetes is being able to respond to a load of dietary sugar. That’s why a glucose tolerance test remains the most sensitive test to diagnose early Type 2 diabetes since it tests what the body is the worst at doing.

The A1c test looks at the last few months of blood sugars, although the most recent month has more of an effect on the A1c than the previous month. So, an A1c, even if it was taken while you were fasting, looks at the whole of your blood sugars during fasting and nonfasting. The A1c is the predominant way we look at overall blood sugar control.

However, in people with prediabetes and those who have established diabetes, sometimes the blood sugar is only high for a short while after eating. The

A1c may not be very high, even if the blood sugar two hours after eating is very high, over 11 mmol/L (about 200 mg/dL).

There are arguments for and against the glucose tolerance test (GTT) in your situation. It is possible that the result will show that you are diabetic, which may give you the motivation to make additional changes in your lifestyle. On the other hand, an A1c level of 6.3% is well-controlled for a diabetic, and medications wouldn’t normally be indicated.

Either approach is reasonable. If you do not get the GTT, you should still get the A1c test a few times a year to see if it is increasing. I would also recommend a visit with a diabetes educator and a registered dietician or nutritionist, both of whom have expertise in preventing and managing diabetes. Finally, there are programs, such as the diabetes prevention program, that provide intensive support to help at-risk people not get a diagnosis of diabetes in the first place.

Dear Dr. Roach: Can you comment on flaxseed for lowering blood pressure? I read people have switched out of medication after using this. I put 1 rounded teaspoon in applesauce or yogurt and mix it in. — B.S.

Dear B.S.: Flaxseed is commonly used as a source for fiber, and flaxseeds reduced cholesterol by about 7 mg/dL in a clinical trial. Flaxseeds have also been studied for blood pressure control, but in a review of all controlled trials, the benefit of flaxseeds was about 2 mmHg, which is almost never enough to make someone stop a medication.

I most often recommend flaxseeds in people with gastrointestinal symptoms, including both diarrhea and constipation. The small reductions of blood pressure and cholesterol are slightly beneficial, but I do not recommend flaxseed just for the treatment of elevated blood pressure or cholesterol.