Data processing: measuring – calibrating – or testing – Calibration or correction system – Linearization of measurement
Reexamination Certificate
2001-06-07
2004-03-23
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Linearization of measurement
C702S028000, C702S030000, C702S104000, C702S085000, C356S042000
Reexamination Certificate
active
06711516
ABSTRACT:
FIELD OF INVENTION
This invention is in the field of spectrophotometric determinations of concentrations of analytes in samples. The invention further relates to methods of calibrating spectrophotometers. Particularly, the method relates to the calibration of spectrophotometric apparatus designed to measure interferents in serum and plasma.
BACKGROUND OF INVENTION
Clinical laboratory tests are routinely performed on serum or plasma of whole blood. In a routine assay, red blood cells are separated from plasma by centrifugation. Red blood cells and various plasma proteins may also be separated from serum by clotting prior to centrifugation. Hemoglobin (Hb), light-scattering substances like lipid particles, bile pigments bilirubin (BR) and biliverdin (BV) are typical substances which will interfere with and affect spectrophotometric and other blood analytical measurements and are therefore referred to as interferents. The presence of such interferents affects the ability to perform tests on the serum or plasma and as such can be said to compromise specimen integrity.
Visual inspection can be used to determine the presence of interferents in serum and plasma but such a method relies on the experience and knowledge of the observer and is therefore unreliable. The use of an apparatus or instrument to measure interferents in serum and plasma i.e., assess specimen integrity, is a substitute for visual inspection and the interferents may be regarded as analytes with respect to the apparatus. Measurement of interferents are taught in WO 9838961 and WO 9839634. Because quantitative results from the determination of the concentration of such interferents are reported based on specific calibration algorithms, there is a need to calibrate and to monitor calibration performance daily.
Unlike many blood analytical apparatus, calibration of reagentless spectrophotometric apparatus used to measure the concentration of analytes or interferents in a serum or plasma sample is a cumbersome time intensive exercise. Each apparatus used for the purposes of determining the concentration of interferents must be calibrated according to procedures known in the art, for example, the process described herein, in the section titled “Primary Calibration,” and over the lifetime of an apparatus can amount to a considerable amount of time and cost. Furthermore, in settings where a large number of apparatus is needed to perform multiple sample measurements (such as blood banks for example) the time required for calibration can become a real burden on the efficiency of the of the quality control process.
Martinek (J. Amer. Med. Technol., July-August 1978, p. 210-216) teaches a method of photometric correction, involving liquid absorbance standards to correct one spectrophotometer to match another using a slope and bias correction. This method may also be used for test methods that require reagents.
U.S. Pat. No. 4,866,644 teaches a method of calibrating a second apparatus to produce results for a test sample, as if the sample was tested on a first apparatus. The method combines photometric correction with a mathematical process that computes a waveshift for each index point. The waveshifts are derived from the assessment of readings determined for a plurality of samples on the two apparatus. The waveshifts are applied as corrections to an existing wavelength calibration table of the second apparatus in order to make the second apparatus behave in a manner similar to the first apparatus. In U.S. Pat. No. 4,866,644, the same wavelengths are assigned to the same corresponding index points in every instrument. Therefore, there is no derivation of a new wavelength calibration table of the second instrument, and the waveshift correction is applied to each measurement as it is determined on the second instrument
WO 94/08225 discloses a method involving the modification of the constants of a primary calibration algorithm of a second or recalibrated apparatus, to yield results consistent with a first apparatus that is in control. A limitation of this method is that the number of samples required must be at least one more than the number of terms used in the primary calibration equation, because a mathematical system of “simultaneous equations” is used to generate a new constant for each term in the primary calibration algorithm. Furthermore, a predicted dependant variable, such as a chemical or physical property, of a calibrator is required to generate the new constants.
WO 97/47972 teaches a method for a second apparatus to produce results for a test sample, as if the sample was tested on the first apparatus involving testing a set of stable samples, whose absorbance spectra mimic that of the analytes, on both the first and a second apparatus, and predicting the analyte concentrations after applying a primary calibration algorithm. This method requires a predicted dependant variable, for example a chemical or physical property, of the calibrator. Analyte results predicted by both apparatus are used to perform a slope and bias correction of each analyte prediction on a test sample. The calibration set requires the property of having an absorbance spectra similar to the analyte.
There is a need for a method to simply and accurately calibrate a second apparatus, and to recalibrate a first or second apparatus that is no longer in control.
It is an object of the invention to overcome disadvantages of the prior art.
The above object is met by the combinations of features of the main claims, the sub-claims disclose further advantageous embodiments of the invention.
SUMMARY OF INVENTION
This invention is in the field of spectrophotometric determination of concentrations of analytes in samples. The invention further relates to methods of calibrating spectrophotometers. The method may be used for the calibration of spectrophotometric apparatus designed to measure interferents in serum and plasma. The invention also relates to a method of transferring calibration algorithms from a first apparatus to a second apparatus.
The present inventor has found that for a given analyte, a “Primary Calibration Algorithm” developed for a “First apparatus” can be transferred onto a “Second Apparatus”. Therefore, the Second Apparatus need not be subjected to the cumbersome, time intensive Primary Calibration process.
In one aspect of the invention, the First Apparatus that is known to be “In Control” is used to assign absorbance values to a “Set of Calibrators” from a batch or lot, and any Second Apparatus can be calibrated rapidly by a process of “Calibration Algorithm Transfer,” and the concentration of an analyte in a sample determined by applying the “Primary Calibration Algorithm” to a corrected interpolated absorbance measurement of the sample. Therefore, the present invention provides a method for calibrating a Second Apparatus using a Set of Calibrators with absorbances assigned by the First Apparatus.
In yet a further aspect of the invention a method for adjusting the absorbance of sample obtained on a second apparatus to normalize it with that of a first apparatus that is in control (“photometric correction”) using a “Linear Regression Equation” is also provided.
The present invention provides a method (A) for a Calibration Algorithm Transfer comprising:
(i) obtaining a first set of absorbance measurements of a set of calibrators on a First Apparatus that is in control at wavelengths from a first wavelength calibration table;
(ii) establishing a second wavelength calibration table on a second apparatus, the first and the second wavelength calibration table may be the same or different, and obtaining a second set of absorbance measurements of the set of calibrators on the Second Apparatus, at wavelengths from the second wavelength calibration table;
(iii) determining a first interpolated absorbance for the first absorbance measurements for at least one wavelength of a Standard Set of Wavelengths, and determining a second interpolated absorbance for the second absorbance measurements for the at least one wavelength of the Standard Set of W
Barlow John
Katten Muchi Zavis Rosenman
Spectromedical Inc.
Vo Hien
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