How to define a cut-off value of tumour markers in haemodialysis patients?

Sir, Biological tumour markers in haemodialyzed patients suffer from a high false positive rate, particularly CEA, C19-9 and CA 125. We conducted a study in haemodialysis patients without diagnosed malignancy to evaluate if a threshold value, defined by the 95th percentile of this cohort, could be proposed for these markers in this population. A total of 105 dosages of each marker were done on 75 patients (immunometric assay, Immulite 2000, DPC). For very high values, markers were monitored at least twice and major causes of elevated level were checked. Twenty patients with normal or high values undertook a second sample to study dosage variability. In 75 patients, the mean value of CEA, CA 125 and CA 19-9 was equal respectively to 4.8 ± 3.9 ng/mL, 25 ± 51 ng/mL and 47 ± 122 U/mL (Table 1). The false positive rate of each marker was concordant with the literature: CEA 34%, CA 125 33% and CA 19-9 22% (Tables 2–4). The 95th percentile of each marker was equal to CEA 12.7 ng/mL, CA 125 119 ng/mL and CA 19-9 294 U/mL. The very high level of the 95th percentile of CA 125 and CA 19-9 does not permit us to define a threshold value. Some very high levels of CA 125 were associated with fluid overload and lessened with the decrease of the dry weight of the patients. The 95th percentile of CEA stands in common values known to be frequent in patients with non-malignant causes of elevated level of this marker. A CEA cut-off value around 13 ng/mL in haemodialysis patients could be proposed using immunometric assay.