ABL800 FLEX Reference Manual 3. Optical measuring principles
Correcting for interferences
HbF versus
HbA
Fetal hemoglobin (HbF) does not have the same spectrum as adult hemoglobin
(HbA) due to a slight variation in molecular structure. The presence of HbF in a
sample will interfere with the result if it is not corrected for.
It is thus important when measuring hemoglobin levels in premature neonates and
neonates aged 0 to 3 months, as well as adults suffering from thalassemia, to take into
account this difference
[3].
The ABL800 FLEX analyzers automatically correct for HbF.
The diagram below shows the transition from fetal hemoglobin to adult
hemoglobin
[4].
This graph is only schematic and cannot be used to determine
FHbF.
Deviation of
Results
If the difference between the two types of hemoglobin is not accounted for in
measurements on samples containing HbF, e.g. from premature neonates and
neonates aged 0 to 3 months, then a deviation in the measurement will arise.
The deviation is most important for measurements of oxygen saturation (
sO
2
) and
the fraction of carboxyhemoglobin (
FCOHb), since inaccurate measurements of
these parameters can lead to incorrect diagnostic interpretation of the results, and
consequent risk of inappropriate treatment.
Detecting HbF
The presence of HbF in a sample is detected from the difference spectrum between
fetal and adult oxyhemoglobin. From the size of the difference spectrum the
concentration of fetal oxyhemoglobin,
cO
2
HbF, can be measured.
The amount of cO
2
HbF exceeding a certain level indicates HbF interference. The
analyzer automatically corrects for this interference by subtracting the difference
spectrum of fetal oxyhemoglobin from the measured spectrum. It then makes
further calculations, using
cO
2
HbF to measure FHbF.
Correcting for
HbF
Continued on next page
3-7
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