Analytical Bias in a Quality Control Scheme - Clinical Chemistry

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1042 ALLEN fT AL Clinical Chemistry himself, he was not aware that lie was using a control sample until after the work was completed. Table 2 presents the coefficient of variation of’ some constituents that appear on Table 1 with those data reported by Straumfjord and Copeland (5). These authors made no mention as to whether their data were derived from known or unknown samples or a combination thereof. Thus, for instance, we might have a problem with our manual phosphorus procedure if Straumfjord and Copeland’s data (5) are derived from unknown samples. The calcium shows a difference between the known and the unknown specimen; the known value compares favoi’ably with the coefficient of variation of these authors. The amylase results are contrary to what we expect with regard to coefficient of variation of the known and blind specimens, and are probably due to the higher mean of the unknown sample (250 versus l0 Somogyi units for the known sample). For the remainder of the procedures our coefficient of variation for the known samples is in the same range as those reported by Straumfjord and Copeland. Although the occurrence of bias in the imonautomated teclinics group, as a whole, was not significant at the 5% level, this does not exclude the possibility that bias may occur in any one method. The ease with which a binomial sign test can be carried out recommends this method as a useful tool for recognizing differences in handling of control samples in a group of procedures. Since we are also reporting the presence of bias in fully automated tests, where, at least in theory, bias should be negligible, one wonders how this bias is introduced. Instrumental inexactness of the sampler phasing in the AutoAnalyzer system has been reported (6, 7). If known control samples are introduced directly after the standards, as in our case, arid only then reported by the medical technologist after he has Table 2. CoMPARISON OF COEFFICIENT OF \ARIATION: OHIO STATE U NIVERSITY IIosPcrus (OcT 1967-MARCH 1968) AND STRAUMFJO RI) & Cul’EJ.AND Specimen O.S.U.I!. Slraumfjord& uaknown - Copeland Cholesterol 6.5 .5. 1 3.5 Alkaline p’tase 6.2 10.6 5.6 Amylase 6.9 8.1 9.7 Calcium 4.0 2.3 2.2 Chloride’ 1.6 1.0 0.8 Glucose 4.2 3.1 2.3 I.P. 6.7 4.9 49 Potassium 3.0 2.5 2.5 Sodium 1.7 1.1 - 0.8 ().S.U.II. known
Vol. 15, No. II, 1969 ANALYTICAL BIAS 1043 convinced himself of initialsatisfactoryperformance of the procedure, these samples failto unmask instrument driftsand specimen interaction (8). Amenta (8) also reported twofold differences in standard errors between samples which in each run were placed in the same position, usually directly after tile standard and duplicate samples which were placed at random. It is generally acknowledged that drifts occur, as evidenced by shifts of known control results. Unfortunately, under the pressure of daily routine and the boredom of reading peak after peak from the recorder, it is virtually impossible to correct for drifts unless the error becomes of such magnitude that the elimination of the underlying malfunction becomes mandatory, or if the error is of lesser magnitude, it call be compensated, for instance, with a computer-aided program. We feel that, at least ill part, a similar situation can occur for automated procedures as that described for manual technics by Robinson (9). Addendum The methods used in this laboratory and listed in Table 1 are itemized below. Some modifications have been made in some of the technics; therefore, reference to the original literature only implies the underlying principle of the technic used. Albumin Kingsley, C. B., J, Biol. Cheni. 133, 731 (1940). I1ove, P. E., J. Biol, Chem. 49, 109 (1921) ; 57, 235 (1923). Calcium Dielul, H., and Ellingboe, J. L., Anal. Chem. 28, 811 (1946). Schwarzenbach, C., Helu. C/jim. Acta 29, 811 (1946) ; 30, 1798 (1947) 32, 1314 (1949); 37, 113 (1954). Chloride AutoAnalyzer modification (N-5a) of the method of Zall, D. M., Fisher, 1)., :uuid Garner, M. 0., Anal. Chenu. 28, 1665 (1956). Creatinine AutoAnalyzer modification (N-ha) of the method of Folin and Wu, taken fu-oun Hawk, Oser, and Sumnmerson, Practical Ph ysiological Chemistry (ed. 12). Blakistone, p 506. Globulin Same as albumin. Glucose AutoAnalyzer modification (N-2a) of the method of Hoffman, W. S., J. Biol. Chem. 120, 51 (1937). 1.1’, Shuiuiow:uu-a, C., Jones, L., ajud Reinluart, 11., .1. L’iol. Chum. 142, 921 (1942). K and Na Auto,\uialyzer technic N-20a, Technicon Coup, Ardsley, NY. Protein Iliuret reaction, total protein and albumin ; Gornall, A. C., Bardewell, C. J., and 1)avid, M. M., J. Biol, Chem. 177, 751 (1949). (le Ia Huerga, J., Smatten, G. W., and Sherrick, J. C., Assoc. Clin. Scientists App1. Seminar on Proteins, Oct 1963, Washiiiigtouu, DC. Urea-N - AutoAnalyzer method for the determination of urea nitrogen in serum (N-la), Skeggs, L. T., Am. J. Clin. Path. 28, 311 (1957). Marsh, W. H., Fingerhut, B., and Kirsch, B., Amer. J. Clin. Path. 28, 681 (1957). Uric acid - AutoAnalyzer method N-13a. Technicout Corp, Ardsley, NY. Cholesterol Leffler, H. H., liner. J. Clin. Path. 31, 310 (1959). Ziathis, A., Zak, B., and Boyle, A. J., J. Lab. CUn. Med. 41, 486 (1953).
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