Lactose Tolerance Test





To assess for lactose intolerance or other metabolic disorders.

Patient Preparation

For the breath test or the glucose challenge test, there are no fluid restrictions unless by medical direction. Inform the patient that antibiotics, laxatives, antacids, and stool softeners should not be taken within 2 wk prior to the test. Fasting for at least 12 hr before the test is required, and strenuous activity should also be avoided for at least 12 hr before the test. The patient should be instructed not to smoke cigarettes or chew gum during the test. Instructions for the breath test may also include brushing the teeth and/or rinsing the mouth with water prior to and during the breath test. Obtain the pediatric patient’s weight to calculate dose of lactose to be administered. Protocols may vary among facilities.

Normal Findings

Method: Spectrophotometry.

Change in Glucose Value*Conventional UnitsSI Units (Conventional Units × 0.0555)
NormalGreater than 20–30 mg/dL above fasting levelGreater than 1.1–1.7 mmol/L above fasting level
Inconclusive20–30 mg/dL above fasting level1.1–1.7 mmol/L above fasting level
AbnormalLess than 20 mg/dL above fasting levelLess than 1.1 mmol/L above fasting level
*Compared to fasting sample for infants, children, adults, and older adults.

Critical Findings and Potential Interventions


Adults and 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).

Timely notification to the requesting health-care provider (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.

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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