Fasting Glucose

Fasting glucose measures the amount of sugar in your blood after you've gone at least 8 hours without eating. It's the simplest, most widely used screen for diabetes and insulin resistance. Because food raises blood sugar quickly, the fasting requirement is what makes the number comparable from one draw to the next, so most panels ask you to test first thing in the morning before eating.

A normal fasting glucose is 70 to 99 mg/dL (3.9 to 5.5 mmol/L). A fasting value of 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is classified as prediabetes, and 126 mg/dL (7.0 mmol/L) or higher on two separate occasions meets the threshold for diabetes. A single high reading should be confirmed, since stress, illness, and a short fast can all nudge the number up.

Divide mg/dL by 18 to get mmol/L, or multiply mmol/L by 18 to go the other way. So a fasting glucose of 90 mg/dL is 5.0 mmol/L, and 100 mg/dL is about 5.6 mmol/L. US labs typically report in mg/dL while most other countries use mmol/L, so the conversion is handy when comparing results across sources.

A fasting glucose of 100 to 125 mg/dL falls in the prediabetes range, so 100 or 105 is mildly elevated rather than diabetic. It's a signal to look at weight, diet, activity, and sleep rather than a diagnosis on its own. Your physician may confirm with a repeat test or an HbA1c, which reflects average blood sugar over about three months and is less sensitive to a single meal or a stressful morning.

In hypogonadal men, testosterone therapy tends to modestly improve insulin sensitivity, which can lower fasting glucose over time. If your glucose is instead rising on TRT, weight gain or worsening insulin resistance is the more likely driver, not the testosterone itself. Sleep apnea, which TRT can aggravate, is another factor worth ruling out, and a rising fasting glucose is best interpreted alongside HbA1c and your physician.