People with diabetes need to consult their physician about often to test glucose (blood sugar) levels. Some patients must test more often than others. Testing three to four times a day, sometimes more, is usually recommended for people who take insulin, because their glucose levels tend to fluctuate more throughout the day. Patients may need to test more often if they are sick or have a change in their normal routine such as an increase in stress or exercise.

Patients aiming for normal or near-normal glucose levels may be advised by their physician to monitor four or more times a day. Studies have shown that when monitoring drops to less than four times a day, glucose control worsens.

People taking anti-diabetic agents will be advised to monitor frequently when their physician is trying to find the right dose or when there is a change in their diabetes care plan, such as an increase in insulin. Once a physician has decided if any changes are needed, recommended monitoring may be reduced to once or twice a day. When diabetes is managed without medications and glucose levels are under control, monitoring might be less frequent.

Useful times for glucose monitoring include:

• Before meals or a big snack (preprandial). Insulin doses can be adjusted based on results.
  
  
• One to two hours after meals or a big snack (postprandial). Results can show the effects of various foods on glucose levels. When a dose of rapid-acting insulin is taken before meal, results can show its effectiveness.
  
  
• Before bedtime. When the reading is low, steps can be taken immediately to raise the level of blood glucose. Insulin doses can be adjusted if results continue to be low.
  
  
• Early morning (2 or 3 a.m.). Early-morning blood glucose tests can provide information on overnight glucose. Insulin doses can be adjusted to prevent nighttime hypoglycemia. Immediate action can be taken to raise glucose levels.

Certain circumstances may result in unusual changes in glucose levels. During such time, additional glucose checks may be recommended. These include:

• Sick days. During illness the body releases hormones to help fight the illness and to promote healing. These hormones can cause an increase in blood glucose.
  
  
• Experiencing shakiness, sweating or other symptoms of low glucose. Results can confirm symptoms are due to hypoglycemia and not something else. Immediate steps can be taken to raise the level of glucose.
  
  
• Experiencing increased thirst, increased urination or other symptoms of high glucose. Results can confirm symptoms are due to hyperglycemia and not something else. Immediate steps can be taken to lower glucose.
  
  
• Menstruation. The hormone fluctuations during the cycle may influence fluctuations in blood glucose.
  
  
• Before driving or operating heavy machinery (especially for patients taking insulin, sulfonylureas or meglitinides). Immediate action can be taken to raise glucose levels that are too low.
  
  
• Increased stress. Stress can cause glucose levels to increase.
  
  
• Increased physical activity. Exercise typically decreases the level of glucose but in some circumstances may increase it.
  
  
• Taking new antidiabetic agents. Many medications may affect patients’ glucose levels or their ability to recognize warning signs of low glucose. Patients are encouraged to discuss these possibilities with their physician or pharmacist.
  
  
• Experiencing frequent insulin reactions (bouts of hypoglycemia) overnight or waking up with very high glucose levels.
  
  
• Change in diabetes management program, such as insulin schedule, eating plan or exercise plan.
  
  
• Weight loss or gain.
  
  
• Hypoglycemia unawareness. 
  
  
• Pregnancy. A diabetic woman may also be advised by her physician to increase glucose monitoring if she is pregnant or thinking about becoming pregnant.
  
  
• Glucose levels have been erratic, severely high or low.
  
  
• Intensive insulin therapy.
  
  
• Administration of glucagon. This emergency treatment for insulin shock (severe hypoglycemia) requires glucose monitoring to determine if an additional injection is needed and if the glucose level has stabilized.