Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (953 page)

   Test in morning after 10–16 hours of fasting. No medication, smoking, or exercise (remain seated) during test.

   Not to be done during recovery from acute illness, emotional stress, surgery, trauma, pregnancy, inactivity due to chronic illness; therefore, is of limited or no value in hospitalized patients.

   Certain drugs should be stopped several weeks before the test (e.g., oral diuretics, oral contraceptives, and phenytoin). Loading dose of glucose consumed within 5 minutes:

   OGTT is not indicated in

   Persistent fasting hyperglycemia (>140 mg/dL).

   Persistent fasting normoglycemia (<110 mg/dL).

   Patients with typical clinical findings of DM and random plasma glucose >200 mg/dL.

   Secondary diabetes (e.g., genetic hyperglycemic syndromes, following administration of certain hormones).

   OGTT should never be used for the evaluation of reactive hypoglycemia.

   OGTT is of limited value for the diagnosis of DM in children.

Suggested Reading

Standards of Medical Care in Diabetes—2014 position statement.
Diabetes Care
. 2014;37(1): S14–S80.

GLUCOSE, CEREBROSPINAL FLUID (CSF)

   Definition

   Glucose in the CSF is about two thirds of the serum glucose measured during the preceding 2–4 hours in normal adults. This ratio decreases with increasing serum glucose levels. CSF glucose levels generally do not go above 300 mg/dL regardless of serum levels. Critical values are <30 mg/dL. Glucose in the CSF of neonates varies much more than that in adults, and the CSF-toserum ratio is generally higher than in adults.

   
Normal range:
50–80 mg/dL.