Interference of alkaline phosphatase on clinical cardiac troponin I assay

Objective To evaluate the interference of ALP on cTnI assays. Methods One normal mixed plasma sample and 2 abnormal mixed plasma samples with different cTnI levels were prepared, and then divided them into 8 groups respectively. One group was randomly chosen as control while different amounts of ALP were added into the other seven groups. The concentrations of cTnI and ALP in each plasma portion were detected by ACCESS2 (Beckman-Coulter, Inc ) and AXSYM (Abbott Laboratories )separately. The results of the seven tested groups were then compared with those of the control, so as to evaluate whether ALP could interfere with the cTnI assay. Results When the chemiluminescent Access cTnI assay was carried out for detection of normal plasma, the concentration of ALP was up to 3 716 U/L and did not interfere with the test results of cTnI [(0. 04 ±0.01) μg/L] compared with those of the control portion [(0. 04 ± 0. 01 ) μg/L] (t = 0. 40, P ＞ 0. 05 ). Once the concentration of ALP went beyond 917 U/L, the AXSYM cTnI assay results [( 0.08 ± 0. 01 ) μg/L] were higher than those of the normal control ( t =-4. 89, P＜0. 01 ); When the concentration of ALP was up to 3 534 U/L, the test results of abnormal plasma cTnI detected by the Access assay [( 13.41 ±0. 17) μg/L] did not show significant differences from those of the control [(13.48±0.16) μg/L] (t=0. 52,P＞0.05).Conclusions High concentration ofALP did not interfere with the Access cTnI assay or lead to false positive results. However, the high level of ALP( ＞ 917 U/L) could interfere with the AXSYM cTnI assay and cause a false positive result. Key words: Alkaline phosphatase;  troponin Ⅰ;  false positive reactions