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Comparative analysis of PSA values measured by MEIA and ELSA techniques in a group of 70 unselected patients. A good correlation was observed between PSA levels determined by ELSA-PSA immunoradiometric techniques and those obtained by MEIA-PSA (r = 0.93, p < 0.00001). However, ELSA-PSA values have been 1.73 +/- 0.1 times higher than those by MEIA-PSA. A mean-paired comparison indicates that PSA mean levels (0.48 +/- 0.07 and 0.29 +/- 0.05 for ELSA and MEIA, respectively) are significantly different and define two groups of nonhomogeneous values (p < 0.0001). The same results are obtained when patients with PSA values higher and lower than 4 ng/ml are analyzed separately. For patients with PSA lower than 1 ng/ml, the difference between mean ELSA-PSA and MEIA-PSA values disappears; 0.74 +/- 0.08 vs 0.62 +/- 0.05, respectively (p > 0.1). In this group, the results from both assays are statistically consistent. When considering the group of patients with PSA < 1 ng/ml, no difference between both techniques becomes apparent, which seems to indicate the absence of differences in sensitivity between both techniques when considering low levels of serum PSA. Nevertheless, it is clear that the results from these techniques can not overlap and are not comparable and so, to all practical effects, it is recommended that follow-up of any particular patient is made always with the same technique and even at the same laboratory.

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