Table 8.

Procedures to identify a false-positive prolactin result due to a heterophile antibody interference¹³

Treatment procedure to patient or control serum and re-assay by VIDAS or alternate assay where indicated	Patient sample Prolactin (μg/L)	Control sample Prolactin (μg/L)	Conclusions
Untreated: □ bioMérieux VIDAS □ Roche Diagnostics Elecsys □ Ortho Diagnostics Vitros ECi □ Abbott AxSYM	>200 21.6 19.1 18.4	- - - -	False-positive Consistent with patient's clinical status
Dilutions in VIDAS prolactin diluent (5- to 320-fold, patient; 2- to 32-fold, control)	117–191% recovery	83–97% recovery	Increasing recoveries for patient sample suggest interference
Addition of mouse, bovine or rabbit serum	No change	-	Insufficient to block interference
HAMA-ELISA assay (immobilised mouse IgG and mouse conjugate)	63 μg/L	-	Weakly positive HAMA
Addition of protein A-Sepharose	No change	-	Not an IgG antibody
Heterophile blocking tubes (Scantibodies; murine IgG directed against human IgM):	17.4 23.3 (Elecsys)	-	Interfering antibody likely to be a natural IgM idiotypic antibody
Precipitation with 25% PEG-6000 and reassay of supernatant	76% recovery (Elecsys)	-	Negative for macroprolactin (>60% recovery)