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.

Blood Glucose

Blood Glucose

Indications

Diagnosis of diabetes mellitus [defined by World Health Organization (WHO) as unequivocal increase of fasting serum (or plasma) glucose > 126 mg/dl on more than one occasion or any glucose level  > 200mg/dL]; Control of Diabetes Mellitus; Diagnosis of hyperglycemia. 

     

Normal Range
Fasting	Post prandial (2hrs)
60 – 100mg/dL	< 140 mg/dL

     

      Higher levels seen in

Diabetes Mellitus including: hemochromatosis, Cushing's syndrome; acromegaly and gigantism, Increased circulating epinephrine due to – adrenaline injection, pheochromocytoma, stress, acute and chronic pancreatitis, effect of drugs like (corticosteroids, estrogens, alcohol, phenytoin, thiazides.)

Lower levels seen in

Pancreatic disorders (e.g. Islet cell tumor, Pancreatitis, glucagons deficiency); extrapancreatic tumors (e.g. carcinoma of adrenal gland and stomach, fibrosarcoma); hepatic disease (e.g. hepatitis, poisoning, cirrhosis, primary or metastatic tumor); endocrine disorders (hypopituitarism, Addison's disease, hypothyroidism); functional disturbances (e.g. postgastrectomy, gastroenterostomy, autonomic nervous system disorders); pediatric anomalies (e.g. prematurity, infant of diabetic mother); enzyme disease (e.g. von Gierke's disease, galactosemia, fructose intolerance others like malnutrition, alcoholism, exogenous, insulin or oral hypoglycemics).  

Activated Partial Thromboplastin Time(aPTT)

Activated Partial Thromboplastin Time(aPTT)

 

Introduction

aPTT is the best screening test for disorders of coagulation; it is abnormal in 90% of patients with coagulation disorders. Screens for all coagulation factors that contribute to thrombin except factor VII and XII. The test may not detect mild clotting defects which seldom cause significant bleeding.

 

Normal range

25 – 38 seconds

Indications and Interpretation

Monitor heparin therapy; Screen for hemophilia A and B,

Prolonged by

Defect in following factors: I, II, V, VIII, IX, X, XI, XII; Presence of specific inhibitors of clotting factors (most frequently antibody against factor VIII, in 15% of patients with hemophilia); heparin, warfarin and lupus anticoagulant.

Normal in

 Thrombocytopenia, Platelet dysfunction, Von Willebrand's disease, isolated defects of factor VII.