The oximetry parameters are calculated as follows:
Parameter Equation ctHb(meas) cO2Hb + cCOHb + cHHb + cMetHb
sO2 2 O Hb eHb c c
ceHb = cHHb + cO2Hb (effective hemoglobin)
FO2Hb 2 O Hb tHb c c FCOHb COHb tHb c c FHHb HHb tHb c c FMetHb MetHb tHb c c FHbF = HbF tHb c c where:
cO2Hb = concentration of oxyhemoglobin in the sample
cCOHb = concentration of carboxyhemoglobin in the sample
cHHb = concentration of deoxyhemoglobin in the sample
cMetHb = concentration of methemoglobin in the sample
cHbF = concentration of fetal hemoglobin in the sample (is not measured directly, but determined on the basis of a definition equation)
Bilirubin is calculated as follows:
Hct(calc) 1 tBil(B) tBil(P) c c where:
ctBil(P) = concentration of total bilirubin in plasma
ctBil(B) = concentration of diluted plasma bilirubin after sample hemolyzation
Hct(calc) = calculated hematocrit (a fraction).
tHb g/dL 0301 . 0 Hct(calc) c
For further details on Hct(calc) please refer to Interference Tests and the explanation of MCHC (Mean Corpuscular
Hemoglobin Concentration) in chapter 7 in this manual.
Oximetry parameters
5-48
The following parameters will not be calculated:
Parameter Is not calculated if…
sO2, FCOHb, FMetHb,
FHHb, FO2Hb
ctHb < 1 mmol/L
sO2 ceHb = cHHb + cO2Hb < 0.75 mmol/L
ctBil ctHb > 14.27 mmol/L
The following conditions are required to perform HbF suppression:
Parameter or Feature Requirement
ctHb > 5 mmol/L
FCOHb < 20 %
FMetHb < 10 % HbF correction –
Enabled for levels >20%
cO2HbF/ctHb should be more than 0.2.
HbF correction –
Enabled for all levels No lower limit value for even adult blood samples will be corrected for HbF. cO2HbF is required, i.e. It may be of value when analyzing blood samples from newborns who have received adult blood transfusion. In these cases FHbF can be lower than
20 % and significant deviations of oximetry parameters and bilirubin can occur.
HbF correction –
Disabled No HbF corrections made.
HbF suppression has
been activated The displayed by the analyzer. FHbF value is normally, but not always, Message "Oxi compensated for HbF" is displayed.
sO2 < 50 % Message "FHbF measurement is not possible" is
displayed by the analyzer, if a HbF suppression has been activated, and the FHbF estimation from cO2HbF is too uncertain.
The uncorrected hemoglobin concentration, ctHb(sample), measured on
capillary or syringe samples is corrected as follows:
cuv tHb(sample) tHb(sample,corr) F c c where: ctHb(sample,corr) = corrected ctHb
Fcuv = analyzer-dependent cuvette path length constant
determined at tHb calibrations and automatically stored by the analyzer
The uncorrected total bilirubin concentration, ctBil(sample), measured on
capillary or syringe samples is corrected as follows:
cuv tBil(sample) tBil(sample,corr) F c c
Fcuv is the same as for tHb.
Corrections for
ctHb
Corrections for
5-50
References
1. CLSI/NCCSL document C12-A, Clinical and Laboratory Standards Institute, 940 West valley Road, Suite 1400, Wayne, PA 19087.
2. Ewing GW. Instrumental methods of chemical analysis. 5th ed. McGraw.Hill, 1985 3. Martens H. Multivariate calibration: quatitative interpretation of non-selective
chemical data: Dr. Techn. Thesuis. NTH Univ. of Trondheim, 1986.
4. Krzeminski A. Why correct for fetal hemoglobin in blood oximetry measurements? Radiometer Publication Info. No. 1992-3. Copenhagen: Radiometer Medical A/S, 1992.
5. Huehns ER, Beanen GH. Developmental changes in human hemoglobins. Clin Dev Med 1971; 37: 175-203.
General information... 6-2 Correction factors for pH and blood gases... 6-4 Correction factors for oximetry parameters ... 6-5 Correction factors for electrolyte and metabolite parameters ... 6-8
6-2
General information
User-defined corrections are most commonly implemented in situations where the values measured for a particular parameter by two or more analyzers deviate consistently from each other.
NOTICE: Since the performance of all ABL90 FLEX analyzers is tested as
described in chapter 7: Performance characteristics in this manual, and each instrument is assumed to operate accurately and optimally, the unnecessary correction of parameter values by the user can lead to inaccurate measurements being reported.
User-defined corrections are based on a linear correlation between the measured values (without user-defined corrections) and the displayed values (with user-defined corrections).
The correction factors for each measured parameter are the slope and the offset of the correction line. With user-defined corrections it is possible to change the values of either one or both of these correction factors, depending on the parameter type.
Corrected value = Slope × Uncorrected value + Offset
The diagram below is a schematic representation of the relationship between correction lines without and with user-defined correction.
Prior to entering corrections for any parameter, the user must obtain the reference values for the chosen parameters, using the method accepted in his/her laboratory. Purpose of use User-defined corrections Preparatory action Displayed (corrected) parameter value (y axis)
Measured (uncorrected) parameter value (x axis)
Offset
Correction line without user correction Correction line with user correction
Slope = 1
It should be noted that in order to define corrections:
Measurements should be taken on the ABL90 FLEX analyzer without user- defined corrections, and on a single reference analyzer
A series of measurements that cover the entire measuring range should be performed
The measurements should be made simultaneously on the ABL90 FLEX and the reference analyzer, and samples must be handled correctly.
The slope and the offset must be calculated. The user may, for example, make a linear correlation between the values measured on the ABL90 FLEX analyzer and the reference analyzer, using the ABL90 FLEX analyzer as an independent variable.
The user must verify the corrections that are entered.
Details of these procedures may be found in the section Test conditions in chapter 7.
The slope/offset for each parameter are configured in General Setup >
Parameters and Input > Parameters. User-corrected values are marked with
a "*" after the result.
NOTICE: The user-defined corrections will be applied to Quality Control
measurements unless the "Apply parameter corrections to QC" option was deactivated in Miscellaneous setup as described in the section Miscellaneous
setup in chapter 1.
For detailed instructions on how to enter user-defined corrections, refer to the section Parameters and input setup in chapter 1.
Entering user- defined corrections
6-4