Patent Application
20060275906
The present invention relates to a method and apparatus for dispensing small liquid samples or other solutions potentially having analytical interferents therein into a container. In particular, the present invention provides a method for accelerating the delivery of small samples for analysis prior to inspecting for the presence of interferents like those that might be found within blood samples tested on an automated clinical analyzer.
Various types of analytical tests related to patient diagnosis and therapy can be performed by analysis of a liquid sample taken from a patient's infections, bodily fluids or abscesses. These assays are typically conducted with automated clinical analyzers onto which tubes or vials containing patient samples have been loaded. The analyzer extracts liquid sample from the vial and combines the sample with various reagents in special reaction cuvettes or tubes. Usually the sample-reagent solution is incubated or otherwise processed before being analyzed. Analytical measurements are often performed using a beam of interrogating radiation interacting with the sample-reagent combination, for example using photometric or fluorometric absorption readings or the like. The measurements allow determination of end-point or rate values from which an amount of analyte related to the health of the patient may be determined using well-known calibration techniques. Unfortunately, the quality of the liquid sample may adversely affect the accuracy of the results of the analyte measurement, in particular if colored interferents are present in the sample as a result of some preexisting sample condition.
For example, if an excess number of red blood cells are damaged, possibly during venipuncture or centrifugation or after prolonged storage, the sample is reddish in color and is said to exhibit “hemolysis.” The presence of free hemoglobin (Hb) may be used to measure the degree of hemolysis and when the hemoglobin concentration exceeds about 20 mg/dl, the hemoglobin may interfere in the calorimetric determination of analytes due to the reddish interferent in the sample.
Another interferent is an excess of bilirubin, the result of the heme of decaying red blood cells being converted in the spleen into bilirubin. Levels of bilirubin above 2-3 mg/dl are visibly yellowish and adversely affect enzyme-based immunoassays in particular. Such a condition is termed bilirubinaemia or icterus.
Another interferent is the whitish appearance in blood serum or plasma due to the presence of excess lipids. Such a condition is called lipemia and lipids levels above about 50 mg/dl may interfere with antibody binding in immunoassays.
A skilled technician will visually inspect the sample, and if judged to not have a normal light yellow to light amber color, the sample may be discarded. Otherwise, the sample will be tested as ordered. However, visual inspection is subjective, labor intensive and fraught with the possibility of human error. Thus, it is desirable to evaluate the integrity of a serum sample without visual inspection by a technician. One approach to this problem involves testing a portion of the sample using the analytical devices of the clinical analyzer prior to analyte assays being performed on the sample by the clinical analyzer. However, this procedure unnecessarily delays the availability of analyte concentration data. Another approach involves testing a portion of the sample simultaneously with performing assays on the sample both using analytical devices of the clinical analyzer. However, because of the trend toward smaller and smaller sample sizes (for patient considerations and to lower reagent costs), the analysis for interferents in a smaller sample portion may be less accurate.
Various methods have been implemented to ascertain whether hemolysis, icteris and lipemia (termed HIL) are present in a serum sample. U.S. Pat. No. 5,734,468 discloses monitoring a serum sample with a detector which performs a spectrophotometric analysis of the serum sample in the probe lumen through a substantially transparent section of the probe. From the spectrophotometric analysis, a hemolytic index, an icteric index and a lipemic index of the serum sample can be established. Based upon these serum indices, the serum sample can be transferred to a clinical analyzer for additional tests or can be disposed of because the sample is compromised.
U.S. Pat. No. 6,372,503 discloses quality control material disclosed is used to monitor instrument calibrations or used for recalibration for instruments which assess the amount of hemolysis, turbidity, bilirubinemia and biliverdinemia, either separately, or any two, or any three, or all four simultaneously, in plasma or serum samples.
U.S. Pat. No. 6,628,395 discloses preliminarily testing a sample for HIL in the original incoming sample container, prior to being removed from the container and prior to being transferred to a clinical analyzer. In this approach, sample is not consumed and can be transferred to the clinical analyzer or a waste receptacle, based upon results of the evaluation.
U.S. Pat. No. 6,353,471 discloses a method to reject a sample from further assay based on determining the concentration of at least one interferent in the sample by: (1) irradiating the sample with at least one frequency of radiation; (2) correlating absorbance of the radiation by the sample with a standard for the interferent(s) to determine the concentration of the interferent(s) and, (3) rejecting the sample if the concentration of the interferent(s) exceeds a predetermined criteria.
Another type of interferent adversely affect the overall quality of the aspiration process are abnormalities or non-uniformities within the sample. Non-uniformities such as clots, bubbles, foam, etc, are found in many samples, particularly when the sample is one of several body fluids as these frequently are of non-uniform composition. Various methods have been developed to detect the effect of such non-uniformities on the aspiration process.
U.S. Pat. No. 6,022,747 discloses a blood clot detector having a pressure transducer on an aspiration line to provide output voltage data to a microprocessor corresponding to the vacuum level during aspiration. The microprocessor integrates the vacuum readings over time during the aspiration cycle to provide a pressure integral for each test sample aspiration. Acceptability of the test sample for analysis is based upon a predetermined difference between a reference pressure integral and each test sample pressure integral.
U.S. Pat. Nos. 5,814,275, 5,622,869 and 5,451,373 relate to an apparatus for detecting obstructions of a flow line. A pressure detector detects changes in pressure within a flow cavity, indicating the presence of an obstruction.
U.S. Pat. No. 5,540,081 relates to a pipetting apparatus provided with clot detection comprising a nozzle for aspirating a sample. A plurality of pressure difference calculating circuits are connected with a pressure sensor, each for inputting an output of the pressure sensor and obtaining a pressure difference at a different pressure calculation period. A plurality of discriminating circuits each having a different discrimination threshold value determined according to each of the pressure calculation periods are provided.
U.S. Pat. No. 5,503,036 relates to an obstruction detection circuit for detecting an obstruction of a sample probe of an automated fluid sample aspiration/dispensation device and a method for detecting such an obstruction. In one embodiment, the obstruction detection circuit includes a pressure sensor measuring the pressure in a fluid conduit connecting a pump and to a sample probe orifice. The pressure within the connecting fluid conduit is measured shortly after the start of the aspiration or dispensation of a sample volume by the automated fluid sample aspiration-dispensation device. The pressure within the connecting fluid conduit is again measured after the completion of the aspiration or the dispensation by the pump, and if the pressure has not returned to a predetermined range within a predetermined amount of time, an error condition is reported.
U.S. Pat. No. 5,463,895 discloses provides an apparatus and method of detecting non-homogeneity in a fluid sample, by determining the ambient air pressure within a pipettor as a baseline reading, aspirating air into the pipettor as the pipettor moves towards a sample in container and monitoring for a pressure change in the pipettor to indicate the surface level of the fluid in said container.
Accordingly, from a study of the different approaches taken in the prior art to the problems encountered with endogenous interferents within small amounts of liquid samples to be tested, there is a need for a method to ascertain the presence of such interferents without adversely affecting the speed at which analytical test results are obtained and without making such a determination on a small sample portion which may adversely affect the accuracy of such a determination. There is a further need to ascertain the presence of sample non-uniformity interferents in a sample without encountering contamination risks associated with making non-uniformity measurement on a small sample portion.
The principal object of the invention is to provide a method for analyzing samples within a biochemical analyzer without either delaying or affecting the accuracy of an analysis thereon. This is accomplished by dispensing small aliquot portions of an incoming sample into reaction cuvettes and immediately proceeding to conduct biochemical analyses thereon without testing for the presence of an interferent therein. Subsequent to this procedure, a larger remaining portion of the sample is tested for the presence of interferents like hemolysis, icteris and lipemia (HIL hereinafter) or liquid non-uniformities therein. By purposefully retaining the larger portion and conducting interferent tests thereon, the accuracy of the testing process is enhanced and the possibility of contamination of the small aliquot portions is eliminated. In addition, because the interferent testing is conducted after the biochemical analyses are begun, there are no delays in obtaining the desired analytical results. If the presence of an interferent is determined, such results may be provided with or separate from the biochemical analyses results obtained on the small aliquot portions of incoming samples. Optionally, if it is determined that no interferent is within the larger sample portion tested therefor, such results may be provided with or separate from the analytical results obtained on the small aliquot portions of incoming samples. An exemplary HIL analysis method measures sample absorption on the larger sample portion at three nanometer (nm) wavelengths from which HIL index values are calculated. The HIL test result comprises the “H”, “I”, and “L” index values as a 3-digit integer in which the first digit represents the “H” index, the second digit represents the “I” index, and the third digit represents the “L” index. The invention provides for biochemical analyses specific “Alert Indices”. Each biochemical analyte analyses may be provided with a specific “Alert Index” value that corresponds to “H”, “I”, and “L” Alert Values. An exemplary liquid non-uniformity analysis method comprises monitoring pressure within a pressure transducer during aspiration of the larger sample aliquot portion subsequent to dispensing small aliquot portions into reaction cuvettes and conducting biochemical analyses thereon.
The invention will be more fully understood from the following detailed description thereof taken in connection with the accompanying drawings which form a part of this application and in which:
Analyzer 10 is controlled by software executed by the computer 24 based on computer programs written in a machine language like that used on the Dimension® clinical chemistry analyzer sold by Dade Behring Inc, of Deerfield, Ill., and widely used by those skilled in the art of computer-based electromechanical control programming. Computer 24 also executes application software programs for performing assays conducted by the assay detection devices 22.
As seen in
Temperature-controlled storage areas or servers 32 and 34 inventory a plurality of multi-compartment elongate reagent cartridges 36 containing reagents accessible by aspiration probe 39 as necessary to perform clinical assays on sample aliquots removed from sample tubes 28 and dispensed into aliquot wells 38 of an aliquot array 40 seen in
As mentioned earlier, an objective of the present invention is to provide a method for accelerating the delivery of small samples for analysis prior to inspecting for the presence of interferents like those that might be found within blood samples tested on an automated clinical analyze without delaying or otherwise affecting the integrity of an analysis thereon. To accomplish this objective, a conventional liquid sampling probe 42 is located proximate the second end of the input lane 30 and is operable to aspirate aliquot portions of sample fluid from sample fluid tubes 28 and to dispense an aliquot portion of the sample fluid into one or more of a plurality of aliquot wells 38 in aliquot vessel array 40. An aliquot vessel array transport system 44 seen in
Subsequent to the dispensing of sample into a cuvette 18, a larger aliquot portion of the sample in the range of about 10 uL is aspirated by aspiration probe 52 from individual aliquot wells 34 and is then dispensed into another cuvette 18 and tested for the presence of interferents like hemolysis, icteris and lipemia and for the presence of non-uniformity interferents like such as clots, bubbles, or foam. By purposefully retaining the larger aliquot portion and conducting interferent tests on the larger portion as opposed to conducting interferent tests on the smaller aliquot portion, the accuracy of the testing is enhanced and the possibility of contamination of the small aliquot portions is eliminated. In addition, because the interferent testing is conducted after the analytical tests are begun, there are no delays in obtaining the desired analytical results. In addition, during aspiration of the larger aliquot portion, the pressure in aspiration
In an exemplary method, the larger aliquot portion is tested for the presence of interferents like hemolysis, icteris and lipemia using photometer 22A wherein the ‘H’ absorbance is derived from blanked, bichromatic measurements at 405 and 700 nm, and the ‘I’ absorbance is derived from blanked, bichromatic measurements at 452 and 700 nm and the ‘L’ absorbance is derived from a blanked 700 nm measurement. Conversion from the absorbance measurements to HIL concentration is computed based on predetermined calibration correlations for all three interferences. The aforementioned HIL indices are associated with the concentration in mg/dL for each of the interferences as specified in Table 1.
An index of 1 represents concentrations of the interferences not normally affecting the analytical feature results. The HIL result, termed the “Sample Index” comprises the ‘H’, ‘I’, and ‘L’ index values as a 3-digit integer XYZ in which the first digit X represents the ‘H’ index, the second digit Y represents the ‘I’ index, and the last digit Y represents the ‘L’ index.
In use, computer 24 will typically be programmed with biochemical assay-specific “Alert Index”. Those assays that exhibit HIL susceptibility will have an Alert Index value that corresponds to ‘H’, ‘I’, and ‘L’ alert values. Alert Indexes can be edited by a user to customize whether a specific method requires HIL checking of the sample, i.e., whether the system will run an HIL along with the associated method, or the minimum HIL index values at which HIL interferences are flagged for a specific method. For example, an assay for glucose might be pre-assigned an HIL Alert Index of “333” and the HIL interferents might be measured as having concentrations of 100, 7 and 500 mg/dl, respectively, using photometer 22A so that the Sample Index is determined from Table 1 as “435”. In this case, the HIL results will be reported as above normal on separate line on an assay report by computer 24 along with all other clinical assay results on the sample. In contrast, HIL might be measured as having concentrations of 20, 3 and 25 mg/dl, respectively, using photometer 22A so that the Sample Index is determined from Table 1 as “221” and the HIL results will be reported as within a normal range. In either case, however, and in accord with the present invention, interferent testing is conducted after the analytical testing so there are no delays in obtaining the desired analytical results.
In another exemplary method of the present invention, the larger aliquot portion is tested for the presence of non-uniformity interferents like such as clots, bubbles, or foam using pressure measuring sensor 62. This method comprises (1) determining a baseline air pressure within tube 60 prior to aspiration of air into probe 52; (2) operating piston 56 to aspirate air into probe 52 as probe 52 is lowered into sample contained in well 38; and, (3) monitoring pressure within tube 60 using pressure measuring sensor 62 during aspiration of the larger sample aliquot portion; and, (4) recording whether or not the monitored pressure remained within a range of values predetermined for samples without the presence of non-uniformity interferents like such as clots, bubbles, or foam. The presence of clots will clog probe 52 causing the monitored pressure to sharply increase while the presence of bubbles or foam will cause the monitored pressure to sharply decrease. The result may be reported as a “Yes/No” non-uniformity interferent result along with analytical results obtained by analyzer 10 on the previously aspirated and analyzed smaller sample aliquot portions. In either case, however, and in accord with the present invention, non-uniformity interferent testing is conducted after the analytical testing so there are no delays in obtaining the desired analytical results and so that the accuracy of non-uniformity interferent evaluation is increased.
It should be readily appreciated by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to specific embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.
