45 Human Chorionic Gonadotropin (hCG) Heterophile Interference Investigations: Experience from a Referral Laboratory

Abstract

hCG quantification by immunoassay is useful in the evaluation of pregnancy and monitoring of gestational trophoblastic diseases and tumors such a germ cell tumors. Heterophile antibody (HA) interference can cause falsely elevated hCG leading to incorrect diagnosis and treatments options. When results are not consistent with the clinical picture, HA interference investigation may be requested by the physician. The purpose of this study was to (1) determine the frequency of HA interference among cases where the physician requested hCG assay interference investigation and (2) evaluate the effectiveness of commercially available blocking reagents to detect HA interferences. Physician requests for hCG HA investigation from 2008 to 2016 were reviewed (n = 112). hCG was measured using the Beckman Coulter UniCel-DxI800 as a primary method and the Siemens Immulite 2000 as the secondary method from 2008 to 2010 (n = 45). From 2014 to 2016, a Roche Diagnostics Cobas e601 was used as the primary method, and Beckman as the secondary method (n = 67). HA investigation included measurement by two immunoassays before and after treatment of samples with heterophile blocking reagent (HBR) nonmurine solution (Beckman assay) and heterophile blocking tubes (HBT) (Roche assay; Scantibodies Laboratory). The absolute difference and the percent difference between untreated and treated results were calculated. Serial dilutions were also performed (primary method) and percent recovery calculated. From the 112 physician requests, five cases of HA interference were identified. The HA frequency was 6.7% (n = 3) for the Beckman assay and 3.0% (n = 2) for the Roche assay. The range of hCG concentrations on all the evaluated samples was 0.1-2,797.0 IU/L (mean 71.1 IU/L; median: 10.2 IU/L). The presence of HA was detected using HBR/HBT reagents in three cases with a percent difference from the untreated sample of –80%, –51%, and –64% from the initial value of 13, 5.5, and 9 IU/L, respectively. The two cases not detected by HBR/HBT reagents were detected due to discrepant results with the secondary method (50.44 vs 1.74 IU/L and 56.6 vs <1.0 IU/L) and nonlinear serial dilution (recovery outside 80%-120%). HA-negative cases showed an absolute difference of ±0.9 IU/L at <10 IU/L and percent difference ≤+/–20% from the untreated at concentrations >10 IU/L for the Beckman assay; and an absolute difference of ±1.2 U/L at <10 IU/L and a ≤+/–10% difference from the untreated at concentrations >10 IU/L for the Roche assay. Frequency of HA interference was similar between the Beckman and the Roche assays (6.7 vs 3.0%, P = .357). The HBR/HBT blocking reagents failed to detect 40% of HA interference cases and should not be solely used for these investigations. Multiple strategies including the use of serial dilutions and measurement using an alternative platform are critical to identify the presence of HA.