OBJECTIVE:
To determine sensibility and specificity that a serum glucose test of normal fast shows respect to control values of chronic glucose patients.

MATERIAL AND METHODS:
Descriptive studies in 610 diabetic patients who used to attend to the clinical analysis laboratory the Zone General Hospital Number 9 of The Social Security Mexican Institute in Ciudad Guzmán, Jalisco, Mexico during 2001. Fast serum glucose tests were carried out as a usual control basis. The tests were based on the determination of fasting serum glucose values and glycosylated hemoglobin.

RESULTS:
Average age of patients was 54.74 ± 14.04 years old. Mean fast serum glucose was 
182.09 ± 80.33 mg/dl (10.01 ± 4.42 mmol/L). 22.3% of patients presented < 120 mg/dl (<6.6 mmol/L). On the other hand, mean glycosylated hemoglobin was 9.46 ± 2.32%. 12% of patients had values <7%. Serum glucose test of normal fast showed a sensibility of 34.23% for the control diagnostic of control values of chronic glucose patients with a specificity of 79.33% to high values of glycosylated hemoglobin. It was also found a predictive positive value of 18.38% and a negative value of 89.87%.

CONCLUSIONS: 
A serum glucose test of normal fast is very little predictive for an adequate control of a chronic glucose patient. A high serum glucose result has much probability that a patient shows high glycosylated hemoglobin.