1. Field of the Invention
This invention relates generally to the determination of fluid chemistries by photometric analysis. In particular, this invention provides methods for determining errors that can arise when using a photometric analyzer to analyze fluid chemistries which result in differential light absorption at different wavelengths.
2. Description of Background Art
Methods for using analyzers to photometrically determine fluid chemistries are known in the art. Before performing the analysis, a fluid sample is provided from a patient, which is typically blood or another body fluid, e.g., urine or saliva. In the case of blood, the sample is placed in a centrifugal rotor which is in turn placed in the analyzer where diluent is mixed with the blood sample. The analyzer rotates the rotor to separate the blood plasma from the blood's cellular components. After centrifugation, quantities of the separated fluid are mixed with diluent. Once the sample and diluent have mixed, the mixture is placed into sample cuvettes mixed with one or more reagents. Light of predetermined wavelengths is then passed through the cuvettes. Some of the light is partially absorbed by the products of the reactions between the reagents and the components of the fluid. The degree to which the light is absorbed at the wavelengths depends upon the concentration of the reaction product in the fluid sample.
By comparing the intensity of the light transmitted through the cuvette with a reference intensity, the concentration of a given product of the reaction between the fluid and the reagent can be determined. The concentration of the reaction is then used to calculate the concentration of a corresponding component in the sample fluid.
When using a photometric analyzer and a centrifugal rotor to determine fluid chemistries as described hereinabove, various errors can arise. For example, too little of the patient's fluid sample can be applied to the rotor. In such a case, the analyzer can produce an incorrect result if the reagents are not mixed with a sufficient sample volume. Similar errors can arise even if an adequate sample is delivered to each cuvette, if the reagent beads in the cuvettes do not dissolve as expected, or if the proper amount of diluent is not mixed with the sample. Errors can also occur if the wrong reagent is placed in a cuvette. Other errors can occur if the fluid sample has not been properly mixed with the diluent, or if the diluent used in the cuvettes is contaminated. Further potential errors can occur if the measurements are affected by system noise or if a chemistry is prematurely evaluated before reaching an end point. Incorrect readings can result if the blood sample is either hemolyzed, lipemic, or icteric, or if the reagents in the rotor itself are spoiled or degraded due to exposure to excessive heat, moisture, light, or other environmental factors.
Thus, it would be desirable to provide methods for detecting these and other problems in order to avoid the reporting of false results and improve the accuracy of the fluid analyzation process. The methods should be able to verify that individual readings and/or groups of readings fall within expected value(s) and range(s) and thus be able to produce an alarm when the readings are improbable and fall outside of the expected value(s) and range(s). The methods should further provide for specific checks to assure that critical functions of the rotor have been successfully completed such as dilution, cuvette filling, reagent dissolution, and the like. It would be further desirable that the methods, when applied to an analyzer, would be usable by individuals with little or no experience in using photometric analyzers.