Theoretical priciples
User Manual Biosen C_line Clinic / GP+
15. Theoretical priciples
15.1 Reference ranges
For specification of reference ranges there must be differentiated
between whole blood glucose and serum/plasma glucose. Based on the
different content of water depending on the hematocrite (Hct: solid parts)
value, the measured glucose value in hemolysed whole blood is always
lower than in plasma and serum, which show the same glucose value.
Normal values of a healthy adult are specified as follows
.
Glucose in whole blood: 3,5 - 5,3mmol/l (65-95mg/dl)
Glucose in serum/plasma: 4,1 - 5,6mmol/l (74-100mg/dl)
For general comparability the IFCC recommends the declaration of
plasma glucose values, which can be calculated from whole blood
values. To this end the IFCC recommends a constant calculation factor
of 1,11. This calculation factor relates to a normal hematocrite value of
43%. A calculation via hematocrite value is not recommended because it
can be a source of additional mistakes. The calculated plasma glucose
value is moderately affected by the hematocrite value. At hematocrite of
59% the displayed value is about 5% too low and at hematocrite of 18%
it is about 6% too high.
15.2 Description of measuring procedure
The measurement of glucose and lactate is based on an electrochemical
measuring principle with a chip sensor specially developed for this
purpose.
The sample is automatically collected by the device and led into the
system. Here the ß-D glucose / L-lactate contained in the sample, is
converted enzymatically with the help of the immobilized enzyme
glucose oxidase / lactate oxidase. The products of the reaction are
gluconic acid/ pyruvate and hydrogen peroxide. The hydrogen peroxide
is detected at the electrode.
Tietz, Fundamentals of Clinical Chemistry, Saunders Elsevier, St. Louis, 2008
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