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False-positive polyethylene glycol precipitation tests for macroprolactin due to increased serum globulins
Sweta Ram1, Beverley Harris, Joseph J R Fernando
1Department of Clinical Chemistry, New Cross Hospital, Wolverhampton, West Midlands, UK.
Background:
The polyethylene glycol (PEG) precipitation test is widely used to detect hyperprolactinaemia caused by macroprolactin. We report two cases of hyperprolactinaemia in which a low recovery of serum prolactin (PRL) after PEG precipitation indicated the presence of macroprolactin, but no macroprolactin was detected by gel filtration chromatography (GFC). Both cases had elevated concentrations of serum globulin (IgG myeloma and polyclonal hypergammaglobulinaemia due to human immunodeficiency virus [HIV] infection), which prompted us to investigate further the effect of serum globulin on the specificity of the PEG precipitation procedure.
Methods:
The effect of increasing concentrations of gamma globulin on the precipitation of PRL by PEG was studied by adding purified human gamma globulin to serum. Ten samples from HIV-infected patients, which showed a low recovery of PRL after PEG precipitation (<60%) were studied with GFC.
Results:
Addition of gamma globulin decreased the recovery of PRL following precipitation with PEG and gamma globulin concentrations correlated inversely with PRL concentrations (r = 0.9429, P < 0.0167) and percentage recovery of PRL (r = -1.000, P < 0.005). Only one out of 10 samples from HIV-infected patients with PRL recoveries of <60% following PEG precipitation showed a substantial macroprolactin component on GFC.
Conclusions:
Monomeric PRL is co-precipitated with serum globulins by PEG. Increased serum globulin concentrations can increase the amount of monomeric PRL precipitated by PEG giving a false estimate of the monomeric PRL and the erroneous impression that macroprolactin is present. The results of the PEG precipitation test should be interpreted with caution in patients with elevated serum globulin concentrations.
Insights
The polyethylene glycol (PEG) test may falsely suggest macroprolactin in hyperprolactinaemia when high serum globulin levels are present. Elevated globulins can interfere with PEG precipitation, leading to inaccurate prolactin (PRL) measurements.
Area of Science:
- Clinical Chemistry
- Endocrinology
- Immunology
Background:
- The polyethylene glycol (PEG) precipitation test is a common method for detecting macroprolactin in cases of hyperprolactinaemia.
- Elevated serum prolactin (PRL) can be caused by macroprolactin, a complex of PRL with antibodies or other proteins.
Observation:
- Two cases of hyperprolactinaemia showed low PRL recovery with PEG precipitation, suggesting macroprolactin, but GFC did not confirm its presence.
- Both cases exhibited elevated serum globulin concentrations (IgG myeloma and HIV-associated hypergammaglobulinaemia).
Findings:
- Increasing gamma globulin concentrations inversely correlated with PRL recovery after PEG precipitation (r = -1.000, P < 0.005).
- PEG precipitation can co-precipitate monomeric PRL with serum globulins, leading to a false impression of macroprolactin presence.
- Only one of ten HIV-infected patients with low PRL recovery (<60%) by PEG precipitation had a significant macroprolactin component detected by GFC.
Implications:
- The PEG precipitation test's specificity for macroprolactin can be compromised by elevated serum globulin levels.
- Results from PEG precipitation tests for macroprolactin should be interpreted cautiously in patients with hypergammaglobulinaemia.
- Further investigation into the interaction between serum globulins and PRL assays is warranted.
