AIIMS Nov 2006 Clinical Sciences MCQ 134

• Bulb for glucose must contain sodium fluoride, so that glycolysis, which starts after about 30 mins after collection, is prevented.
  
• Enolase is a homodimer that is inhibited by fluoride, with formation of the magnesium
  fluorophosphates complex at the active site.
  
• This property of fluoride is used to inhibit
  glycolysis in blood specimens obtained for measurement of glucose concentration. In the absence of fluoride (or any other antiglycolytic agent), the blood glucose concentration decreases ast about 10 mg/dL per hour at 25oC.
  
• The rate of decrease is more rapid in blood from newborn infants owing to the increased metabolic activity of the erythrocytes and in leukemia patients because of the larger numbers of leukocytes.

• But the same chemical being toxic to enzymes, the enzyme dependant tests, like urea, creatinine, serum enzymes, reduces the values markedly and hence should not be used for such tests.
  
• Also the preparation of the anticoagulants should be proper. Even preparation of such bulbs matters : Adding 1 - 2 granules of anticoagulants powder produces macrocoagulation if not properly swirled immediately.
  
• Bulbs prepared by adding dissolved anticoagulant in proper portion and then drying is the best method.
  
• Citrate bulb for prothrombin time contains citrate solution just necessary and sufficient for 2 ml blood. Smaller or larger quantity of blood by itself alters prothrombin time significantly.

Category: AIIMS Nov 2006 MCQs