Blood Sugar 159 mg/dl — Too High? Fasting & After Eating

Running a fever and reading 159

Infections raise blood sugar. When the body fights a virus or bacteria, it releases stress hormones such as cortisol and adrenaline, which push the liver to release glucose and make tissues less responsive to insulin. Fever adds to the effect. A reading of 159 during a bad cold, the flu, a urinary infection or a chest infection is common, even in people whose usual numbers are much lower.

For someone without diabetes, an isolated 159 during an illness is not a diagnosis; test again once you have recovered. For people with diabetes, illness is a time to follow “sick-day rules”, ideally agreed with the care team in advance.

The link runs both ways. Glucose that stays high makes white blood cells less effective, which can make infections linger. Keeping numbers in a reasonable range while you are ill helps recovery, which is another reason not to let checking and medicines slide just because you feel too unwell to bother.

Sick-day rules in plain terms

• Keep checking. Test more often than usual, commonly every few hours while you are unwell, and write the results down. Numbers can change quickly.
• Drink plenty. Sip water or other sugar-free fluids regularly. High glucose and fever both cause fluid loss.
• Keep some carbohydrate coming. If you cannot eat normal meals, small amounts of easy foods or drinks with carbohydrate, such as soup with crackers, juice or regular soda in small sips, can prevent lows when you take medicine.
• Do not stop insulin. Even when you are not eating, the body needs basal insulin, and illness often raises the need. Ask your team how to adjust.
• Ask about other medicines. Some diabetes tablets are usually paused during illness with vomiting or dehydration. Your care team or pharmacist can tell you which ones and when to restart.

Ketones and type 1 diabetes

For people with type 1 diabetes, and some others on insulin, illness is the most common trigger for ketone build-up. ADA advises checking ketones when glucose is above about 240 or whenever you are ill, even at lower readings. Ketones can rise when insulin is short, which is why skipping insulin during illness is risky. Moderate or large ketones call for prompt contact with the care team. Keep in-date urine strips or a blood ketone meter at home, because a pharmacy run is hard when you are already sick.

When to call, and when to call 911

Contact your care team if you cannot keep fluids down, if readings stay well above your usual range despite following your plan, if ketones are moderate or high, or if you have had a fever for more than a day or two without improvement.

Call 911 for repeated vomiting with high glucose or ketones, deep or rapid breathing, a fruity smell on the breath, confusion, severe drowsiness, or signs of severe dehydration. These can point to diabetic ketoacidosis (DKA) or a hyperosmolar state (HHS), which are emergencies.

A 159 alone is far from those situations. The point of sick-day rules is to keep it that way. The how to test blood sugar guide covers checking technique.