DETERMINATION OF CARCINOEMBRYONIC ANTIGEN (CEA) - COMPARISON OF 2 DIFFERENT ASSAYS

  • 1 January 1978
    • journal article
    • research article
    • Vol. 86  (6) , 265-275
Abstract
A comparison was made of CEA determination by the CEA-RIAKIT and our slightly modified CEA-Roche assays. The normal levels (mean + 2 SD) found in 63 blood donors were 2.3 .mu.g/l and 3.3 .mu.g/l, respectively. The interassay reproducibility was similar in the range below 15 .mu.g/l, with variations from 0.3 .mu.g/l (1 SD, < 5 .mu.g/1) to 1.4 .mu.g/l (1 SD, 10-15 .mu.g/l). Both methods measured CEA concentrations down to 1 .mu.g/l. The ability of the 2 assays to discriminate between positive and negative values in patients with urogenital and gastrointestinal cancer was similar. The response to recurrences of colorectal carcinoma was also similar, and the CEA fluctuation was parallel after surgery. The CEA-Roche assay generally showed good correlation between measured and theoretical values at both low and high levels. Under our test conditions, the disparity between indirect and direct values was 14 .mu.g/l .+-. 8 (n = 4) in the range 18-32 .mu.g/l, and this must be taken into consideration in interpreting the CEA-Roche test. The CEA-RIAKIT measured too low values as compared to the CEA-Roche and the theoretical values. The discrepancy increased with increasing CEA values, and the ability to distinguish between high CEA concentrations (> 15 .mu.g/l) was poor. The anti-CEA sera used in this assay apparently show a lower affinity for plasma CEA than for tumor-extracted CEA. Immunochemical differences between sample CEA and CEA used for calibration of the standard curves must be considered in evaluation of CEA assays.

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