Theoretical Principles; Reference Ranges; Description Of Measuring Procedure - EKF Diagnostics Biosen C-Line Clinic User Manual

9. THEORETICAL PRINCIPLES

9.1 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 hematocrit (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:
Glucose in serum/plasma:
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.

9.2 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.
The resulting current is proportional to the glucose/lactate concentration. Unknown
glucose/lactate concentrations can be determined relative to a calibration with
a solution of known concentration. After each measurement the chip sensor is
automatically cleaned with a buffer solution. This washes out the old sample substance.
The sensor system is then ready for the next measurement.
Tietz, Fundamentals of Clinical Chemistry, Saunders Elsevier, St. Louis, 2008
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3,5 - 5,3 mmol/l (65-95 mg/dl)
4,1 - 5,6 mmol/l (74-100 mg/dl)
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