Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
  • G01N21/274—Calibration, base line adjustment, drift correction

Definitions

• the present invention relates to a method for examining a fluid according to the preamble of claim 1. It relates further to devices for executing the method.
• In vitro interferences arise from the fact that biochemical analysis are performed in the complex matrices that make up biological fluids, e.g. serum, plasma or urine. These fluids contain numerous compounds that either have chemical groups that can react with the test reagents or can have the physical or spectral properties of the target analyte. Further, the chemical composition of body fluids can vary with the nature and the extent of disease processes. In vitro interferences can be classified into two classes: spectral and chemical interference.
• hemolysis The most commonly observed interferences are hemolysis, icteria, and lipemia. Some 30 % of samples obtained from clinic or hospitalized patients are he olyzed, icteric, or lipemic. Main reasons for hemolysis are unskilled blood taking or sample preparation, for icteria the jaunice disease, and for lipemia fat nutrition before blood taking.
• sample quality monitoring is the determination of the interfering substances hemoglobin, bilirubin, and lipid prior to conducting fully automated clinical laboratory tests in order to provide meaningful and accurate test results. If a sample is sufficiently contaminated with interference substances, the test may either not be conducted or the test result may be flagged to indicate that it is not reliable. Particularly, such a test is desirable in connection with the use of clinical-chemical analyzers which perform most of the analysis of a sample fully automatically and without taking into account any particular characteristics or properties of individual blood samples.
• the combination or superposition of the extinction spectrum of this first one of the components in a pure state and a function approximating the background extinction is fitted to the measured spectrum of the fluid to be analyzed in a wavelength range, where the component to be determined shows a significant or characteristic shape of its extinction curve.
• the function approximating the background extinction may e.g. be a straight line, and in this case, the wavelength range is preferably chosen where the expected background extinction spectrum is similar to a straight line .
• Fig. 1 Schematic representation of a photometric spectrum measurement arrangement.
• Fig. 2 Extinction spectra of pure interfering substances and a standard blood serum.
• Fig. 3 Normalized extinction spectra of real whole blood sera, bilirubin and hemoglobin contribution being subtracted, and a reference lipid solution sample.
• Fig. 4 Evaluation method for sample quality monitoring.
• Fig. 5 Experimentally measured extinction spectrum of a real whole blood serum and results of the evaluation method.
• Fig. 6 Measured extinction spectrum of a strongly hemolytic whole blood sample and respective extinction spectra obtained by the examination method.
• Fig. 7 As Fig. 6 for a strongly icteric whole blood sample.
• Figs. 8, 9 Optically determined hemoglobin (Fig. 8) and bilirubin (Fig. 9) concentrations versus added concentrations for 125 independent test samples.
• Figs. 10,11 Optically measured hemoglobin respectively bilirubin concentration values vs. clinical- chemically measured concentration values for independent real whole blood sera.
• Figs. 12-15 Optically measured hemoglobin and bilirubin concentrations of 92 real whole blood sera and the respective CV values obtained using a state-of-the-art spectrometer.
• Fig. 16, 17 Low-cost versus state-of-the-art spectroscopically measured (Fig. 16) hemoglobin and bilirubin (Fig. 17) concentrations of 92 real whole blood sera.
• Fig. 18 Schematic illustration of a dip probe.
• a method according to the invention for sample quality monitoring of blood serum or plasma by optical absorption spectroscopy in the visible and near IR range is described hereinafter.
• the evaluation performed by the method according to the present invention yields e.g. the content of the hemoglobin and bilirubin.
• a quantitative determination of the lipid concentration by optical absorption spectroscopy is not possible due to a lack of a reproducible relation between light-scattering and lipid concentration.
• a differential extinction spectrum is obtained by subtracting the hemoglobin and bilirubin contributions from the extinction spectrum of the target sample. It contains the spectral contributions of the lipid and the matrix, e.g. the blood serum or plasma, which can then be investigated for spectral anomalies.
• the method has been experimentally tested using a series of 125 synthetic test samples and a series of 92 real blood sera. Accuracy and reproducibility of the technique versus the performance of the spectroscopic measurement device are described and commented hereinafter.
• FIG. 1 A basic setup for optical absorption spectroscopy for sample quality monitoring is shown in Fig. 1.
• a light beam 1 emitted by a multiple optical wavelength light source 2 is collimated by a lens 3, which directs light of spectral intensity Io( ⁇ ) to a target sample 6.
• the optical path within the target sample is denoted by d.
• a lens 4 collects transmitted light of intensity I ( ⁇ ) , which is then detected by a spectral wavelength analyzer which has an input 5.
• Optical absorption is commonly characterized by the extinction E ( ⁇ ) , which is defined as
• the extinction E ( ⁇ ) of the target sample can be described by the linear combination
• the solid line 30 represents the extinction spectrum of the reference solution of Intralipid, the broken lines 31 represent the extinction spectra of several samples of real whole blood sera after subtraction of the extinction contributions of hemoglobin and bilirubin.
• a sequential determination of first the hemoglobin (C H ) and then the bilirubin (C B ) concentration is proposed in order to obtain a differential spectrum E dlff by subtracting the hemoglobin and bilirubin contributions from the measured extinction spectrum E ( ⁇ ) .
• the differential spectrum E dlff thus represents the sum of the contributions of the lipid (E L ) and the matrix (E g ) to the extinction spectrum E ( ⁇ ) of the target sample, and may additionally be investigated for spectral anomalies over the whole spectral range.
• a first step 32 the hemoglobin concentration is determined from a first measured extinction spectrum E x ( ⁇ ) in a wavelength range ⁇ rh ⁇ [545, 575] nanometer.
• a set of extinction values comprising those of spectrum Ei ( ⁇ ) is represented by block 35.
• Fig. 2 within the wavelength range ⁇ rh ⁇ [545, 575] nanometer hemoglobin has typical spectral characteristics and the bilirubin contribution to the extinction spectrum is quasi negligible (Fig. 2) .
• E H ( ⁇ ) is the hemoglobin contribution and is defined by
• Fitting step 37 delivers the best estimate of the values of the hemoglobin concentration C H and a 0h , a ih . This set of values is represented by block 38.
• the bilirubin concentration is determined from a second measured extinction spectrum E 2 ( ⁇ n ) in the wavelength range ⁇ rb ⁇ [480, 545] nanometer.
• a set of extinction values comprising those of spectrum E 2 ( ⁇ ) is also represented by block 35.
• Fitting step 41 delivers the best estimate of the bilirubin concentration C B and a 0 b, a ⁇ b .
• This set of values is represented by block 42.
• the set of values of E dlff is represented by block 45. This set of values can then be investigated for spectral anomalies and lead to results represented by block 46 which can be in particular indicative of an anomalous lipid content of the target sample.
• the method according to the invention can be used to determine the concentration of k pure substances contained in a target sample.
• the method according to the invention comprises:
• the approximated spectrum E ] _( ⁇ ) is the sum of said predetermined approximation function Edi( ⁇ , a 1#S ⁇ ) for the background extinction, and said predetermined extinction spectrum E S ⁇ (C S ⁇ , ⁇ ) of said pure first component of concentration C S ⁇ .
• E dk ⁇ , a 1/S
• the approximated spectrum E k ( ⁇ ) is the sum of said predetermined approximation function E dk ( ⁇ , a 1 S k) for the background extinction, said previously determined extinction spectrums E SL (C S L, ⁇ ), with L varying from to k-1, of k-1 pure components previously determined, and said predetermined extinction spectrum
• ⁇ is the center wavelength of the respective measurement range ⁇ r .
• ln(x) is the natural logarithm of (x) .
• a method step 48 for computing the coefficient of variation CV of the measured hemoglobin concentration, and a method step 49 for computing the coefficient of variation CV of the measured hemoglobin concentration are represented.
• Equation (9) it can be appreciated that the reproducibility of the measured concentration increases with the number N of measured extinction values considered for the curve fitting method step.
• the number N is given by the spectral resolution and sampling rate of the spectroscopic measurement system and the wavelength range ⁇ r .
• Sample quality monitoring based on optical absorption spectroscopy as shown in Fig. 1, has been experimentally investigated using a state-of-the-art spectrometer (Cary V, VARIAN, Australia) .
• the collimated beam had an approximate spot size of 5 x 2 square millimeter.
• the differential extinction spectrum E dlff has been obtained from Equation (7) .
• Figure 5 shows the experimentally measured extinction spectrum E( ⁇ ) of a typical real whole blood serum 55.
• the best fitting extinction models for hemoglobin 57 and bilirubin 59 in Equations (3) and (5) are represented by crosses and dots, respectively.
• the differential extinction spectrum E dlff ( ⁇ n ) 60 is also shown by the dashed line.
• Figs. 6 and 7 show other examples of real whole blood serum samples, namely with a high hemoglobin content respectively an highly icteric sample. Furthermore, in Fig. 6, the differential spectrum shows an anomalous differential spectrum which is merely constant with additionally an increased extinction with increasing wavelength above about 650 nanometer.
• the continuous line 62 is the measured spectrum
• the dashed line 64 and the dotted line 65 are the hemoglobin respectively the bilirubin contributions
• the dash-dotted line 66 is the differential spectrum, each time calculated from the results according to the described method.
• the hemoglobin and bilirubin concentrations of a series of 125 independent test samples have been determined.
• the samples have been synthesized using a standard blood serum (Control Serum N (human) [Hoffmann-La Roche, Switzerland] ) to which hemoglobin (Hemolysat [Hoffmann-La Roche, Switzerland] ) , bilirubin (B-4126 mixed isomers [Sigma, Switzerland] ) and lipid (Intralipid 20% [Pharmacia, Sweden] ) have been added.
• the optically measured hemoglobin 70 and bilirubin 72 concentrations versus added concentrations are represented in Fig. 8 and 9.
• Control Serum N human has an approximate bilirubin concentration of C B ⁇ 2 mg/dl. Further, it is stated that the amount of added hemoglobin, bilirubin and lipid also has finite accuracy.
• the hemoglobin and bilirubin concentrations of a series of 92 real whole blood sera have then been optically determined.
• the concentrations have been determined by clinical-chemical analysis (Cobas ® Integra 700 analyzer, [Hoffmann-La Roche, Switzerland] ) .
• Figures 10 and 11 show the optically versus clinical-chemically determined hemoglobin [bilirubin] concentrations 90 [91].
• the sensitivity of the method is approximately C H ,m ⁇ n ⁇ 0.5 g/1 hemoglobin and C B ,m ⁇ n ⁇ 2 mg/dl bilirubin.
• the clinical-chemical method has also limited accuracy; namely the bilirubin concentrations (Fig. 11) show better correlation than the hemoglobin concentrations (Fig. 10) , although the accuracy of the optically measured bilirubin concentration is affected by the accuracy of the hemoglobin concentration determination (sequential determination of hemoglobin and bilirubin, see above) .
• FIG. 12 shows the optically measured hemoglobin (Fig. 12) and bilirubin (Fig. 14) concentrations of the set of 92 real blood sera and the respective CV values (Fig. 13 respectively Fig. 15). Inspection of Figs. 12 to 15 shows that the reproducibility is better for large concentration values, and that the values for hemoglobin and bilirubin are better than CV ⁇ 10 % respectively ⁇ 1 % for 89 respectively 91 of 92 analyzed sera.
• the light was spectroscopically analyzed by a low cost, plane-concave spectrometer PCS [CSEM-Z, Switzerland] with spectral resolution ⁇ ⁇ 8 nanometer.
• the bilirubin concentration C B has been obtained from linear least squares fitting the model in
• the differential extinction spectrum E ⁇ i ff has been obtained from Equation
• Figures 16 and 17 show the PCS versus the state-of-the- art (Cary V) spectroscopically measured hemoglobin respectively bilirubin concentrations of the set of 92 blood sera of Figs. 10, 11 and 12 to 15.
• bilirubin Fig.
• the examination of the samples yields a result indicating an anomalous condition of the sample, there may be generated by the examining device, e. g., one or more of the following signals or responses:
• the described method may be implemented in various arrangements, preferably in connection with an automated analyzer, e g. as follows:
• the quality test may be done as a first photometric pass in the photometric site of an analyzer. Thereby, the performance of the analyzer is reduced because this prescan and the regular photometric pass are performed subsequently, or an additional sample is needed causing consumption of sample material; - An additional photometric site is provided for the quality test;
• the pipette or more generally, the supply system of the analyzer for the fluids to be tested, is provided with a transparent site, i. e. an optical flow-through cell (OFTC) , in connection with a photometer; where necessary, particularly when the conduit system subsequently provides differently diluted samples, there may be arranged different OFTC paths with different optical path lengths in connection with flow switches for compensating the varying dilutions;
• OFTC optical flow-through cell
• a dip-in probe 110 having e.g. a structure of the type shown by Fig. 18.
• Probe 110 has a tubular body 111 and is adapted to be immersed into a liquid sample contained in a sample container.
• Light guides 115 and 119 are arranged within and extend along the length axis of tubular body 111.
• Tubular body 111 has an end part 112 and a recess
• Tubular body has a segment
• lens 117 and 118 and a prism 116 arranged within tubular body 111 at the end 112 thereof complete the structure of dip- in probe 110.
• Light transmitted through light guide 115 and lens 118 impinges on and is reflected back by prism 116, traverses recess 113, where a volume of the liquid sample to be examined is present, is collected by lens 117 and is transmitted to a photometer via light guide 119.
• the sample tube itself may be used as the photometric cuvette, provided the differing lengths of the optical observation paths can be compensated for, i. e. the path lengths are determined and can be input into the quality test system, and/or the sample tubes are of sufficiently equal size so that the optical paths do only differ within small limits, maybe in an even negligible variation range.
• tubular body 112 end part of tubular body 111

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• 1999
  • 1999-06-11 EP EP99810517A patent/EP1059522A1/en not_active Withdrawn
• 2000
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