Table 1. Serum hCG concentration using kits and analysers from different manufacturers and the effect of pre-incubation in heterophilic blocking tubes (for all measurements, the first sample obtained during hospitalization at the university hospital was used).

Reagent kit, instrument (company)	hCG (U/L)
Total β-hCG, Architect i1000SR analyser (Abbott, Abbott Park, USA)	2265
Total β-hCG, Architect i1000SR analyser (Abbott, Abbott Park, USA), after pre-incubation in a heterophilic blocking tube	< 1.2
ELECSYS hCG+βb, Cobas e602 analyser (Roche Diagnostics GmBH, Mannheim, Germany)	< 1.0
Access Total Beta-hCG, Unicel DxI 800 Access Immunoassay System (Beckman Coulter, Brea, USA)	4.2
hCG - human chorionic gonadotropin.