Glucose is a topic covered in the Davis's Lab & Diagnostic Tests.

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Blood sugar, fasting blood sugar (FBS), postprandial glucose, 2-hr PC (post cibum).

To assist in the diagnosis of diabetes and to evaluate disorders of carbohydrate metabolism such as malabsorption syndrome.

Patient Preparation
There are no activity or medication restrictions unless by medical direction. There are no restrictions for the random glucose test. Instruct the patient to fast for at least 8 hr before specimen collection for the fasting glucose test and not to consume any caffeinated products or chew any type of gum before specimen collection; these factors are known to elevate glucose levels. Instruct the patient to follow the instructions given for 2-hr postprandial glucose test. Some health-care providers (HCPs) may order administration of a standard glucose solution, whereas others may instruct the patient to eat a meal with a known carbohydrate composition.

Normal Findings
Method: Spectrophotometry.

AgeConventional UnitsSI Units (Conventional Units × 0.0555)
Nondiabetic, fasting
 Cord blood45–96 mg/dL2.5–5.3 mmol/L
 Premature infant20–80 mg/dL1.1–4.4 mmol/L
 Newborn 2 days–2 yr30–100 mg/dL1.7–5.6 mmol/L
 Child60–100 mg/dL3.3–5.6 mmol/L
 Adult–older adultLess than 100 mg/dLLess than 5.6 mmol/L
Nondiabetic, 2-hr postprandial65–139 mg/dL3.6–7.7 mmol/L
Nondiabetic, randomLess than 200 mg/dLLess than 11.1 mmol/L
Prediabetic, fasting100–125 mg/dL5.6–6.9 mmol/L
Prediabetic, 2-hr postprandial140–199 mg/dL7.8–11 mmol/L
Fasting means no caloric intake for 8 hr or longer. Values tend to increase in older adults.

Critical Findings and Potential Interventions


Adults & children
  • Less than 40 mg/dL (SI: Less than 2.22 mmol/L)
  • Greater than 400 mg/dL (SI: Greater than 22.2 mmol/L)

  • Less than 32 mg/dL (SI: Less than 1.8 mmol/L)
  • Greater than 328 mg/dL (SI: Greater than 18.2 mmol/L)

Timely notification to the requesting HCP of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

Glucose monitoring is an important measure in achieving tight glycemic management. The enzymatic GDH-PQQ test method may produce falsely elevated results in patients who are receiving products that contain other sugars (e.g., oral xylose, parenterals containing maltose or galactose, and peritoneal dialysis solutions that contain icodextrin). The GDH-NAD, glucose oxidase, and glucose hexokinase methods can distinguish between glucose and other sugars.

Symptoms of decreased glucose levels include headache, confusion, polyphagia, irritability, nervousness, restlessness, diaphoresis, and weakness. Possible interventions include oral or IV administration of glucose, IV or intramuscular injection of glucagon, and continuous glucose monitoring.

Symptoms of elevated glucose levels include abdominal pain, fatigue, muscle cramps, nausea, vomiting, polyuria, polyphagia, and polydipsia. Possible interventions include fluid replacement in addition to subcutaneous or IV injection of insulin with continuous glucose monitoring.

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