Oral Glucose Tolerance Test (OGTT)

Oral Glucose Tolerance Test (OGTT)

      Introduction

OGTT is done after overnight fasting for 10 –16 hrs. Certain drugs should be stopped several weeks before the test (e.g. oral diuretics, 0.Cs phenytoin). Loading dose of glucose [adults = 75gms, for children 1.75gm/kg (of ideal body weight in obese children but never > 75gms). Pregnancy = 100gms] is consumed in 5 mins. Blood sample drawn at fasting, 30, 60, 90, 120 mins.

Indications

OGTT should be reserved principally for patients with '' borderline'' fasting plasma glucose levels ( i.e. fasting range 110 – 140 mg/dL).

All pregnant women should be tested for gestational diabetes with a 50gms dose at 24 – 28 weeks of pregnancy; if result abnormal, OGTT should be performed after pregnancy.

Increased tolerance in 

Pancreatic is let cell hyperplasia or tumor, poor absorption from gastrointestinal (Gl) tract in intestinal disease (e.g. steatorrhea, sprue, colic disease), hypothyroidism Addison's disease, liver disease, hypopituitarism.

 Decreased tolerance in   

Diabetes mellitus- For diagnosis of diabetes in nonpregnant adults, at least two values of OGTT should be increased (or fasting serum glucose > 140mg/dL on more than one occasion and other causes of transient glucose intolerance must be ruled out.

                Other causes of decreased tolerance are hyperthyroidism, hyperlipidemia, steroid effect, Cushing's effect, administration of adrenocorticotropic hormone (ACTH) or steroids, pregnancy.

Drugs like indomethacin, various neuroactive drugs (phenothiazines, tricyclics, lithium, haloperidol), heparin.