Detection and characterization of estradiol (E2) and unconjugated estriol (uE3) immunoassay interference due to anti-bovine alkaline phosphatase (ALP) antibodies

Asymptomatic elevation of parathyroid hormone levels by antibodies against reagent alkaline phosphatase

CONTEXT

Although immunoassay interference is a well-known phenomenon, its detection in routine clinical practice remains challenging. Most immunoassay interference can be attributed to the presence of heterophilic or anti-hormone antibodies. However, reports on immunoassay interference specifically related to parathyroid hormone (PTH) are scarce.

CASE DESCRIPTION

A 77-year-old woman with hypertension, nephrotic syndrome, and high PTH levels for one year was admitted to our Surgical Department for treatment. The patient had no specific symptoms and normal calcium and alkaline phosphatase (ALP) levels but markedly elevated PTH levels. PTH was 2172 pg/mL using the Beckman Coulter system, whereas the Roche, Abbot, and Siemens systems yielded normal results. PTH concentration decreased to 63.8 pg/mL after pretreatment with polyethylene glycol 6000 and did not decrease to normal levels following pretreatment with heterophilic blocking tube-50 (HBT-50), heterophilic blocking reagent (HBR)-21, or HBR-25. When the HBR-21 concentration was increased, serum PTH decreased to 99.0 pg/mL. After treatment with scavenger bovine alkaline phosphatase (inactive), the concentration of PTH decreased to a normal value (51.3 pg/mL). Additionally, PTH (1-84) concentration was 17.6 pg/mL using LC-MS/MS.

CONCLUSION

PTH was falsely evaluated due to anti-bovine ALP antibodies (antibodies against reagent ALP). Anti-bovine ALP antibodies should be considered in assays that use ALP as a signal generator.

Falsely Elevated Estradiol Results in a 62-Year-Old Male Patient

Falsely increased estradiol levels can lead to unnecessary tests and therapeutic interventions. Here, we present a case of a 62-year-old man with falsely elevated estradiol, which led to subsequent follow-up testing and prescriptions. Alternative immunoassay testing, in conjunction with Scantibodies' blocking reagents, polyethylene glycol precipitation, and liquid chromatography-tandem mass spectrometry confirmation demonstrated that the falsely elevated estradiol was due to the presence of macro-estradiol. This report emphasizes the importance of recognizing analytical interferences in immunoassays to appropriately manage subsequent testing and patient care.

Impact of Unconjugated estriol (uE3) assay interference on prenatal screening tests

BACKGROUND

Unconjugated estriol (uE3) is an important biomarker in second trimester prenatal screening. Previous studies from our laboratory identified rare interference in the Beckman uE3 assay due to anti-ALP antibodies, which could be mitigated with a scavenger or heat-inactivated ALP (hALP). In the current study, 160 de-identified patient samples previously submitted for the Quad screen with low uE3 multiples of the median (MoM ≤0.50) were investigated for potential interference.

METHODS

A reagent pack spiking strategy with hALP was employed to understand if the interference could be identified and mitigated in a scalable manner. The 160 samples were measured using uE3 lot #920861 previously known to be subject to interference, lot #920861 spiked with hALP, and the vendor reformulated lot #922579. Samples were suspected to have interference if the percent difference in uE3 measurements was >50%. Pseudo-risks were calculated using a test patient environment to understand the screening impact due to the change in uE3 result.

RESULTS

Seventeen of the 160 samples had uE3 results that were >50% different between the hALP spiked and non-spiked reagent pack. Both original lot #920861 with hALP and reformulated lot #922579 identified the same 17 patients as having interference in lot #920861. Analysis of screening risks using a test patient environment showed that assay interference could result in false positives for one trisomy 21 and three trisomy 18 post-test risk calculations.

CONCLUSION

Our experiment of reagent pack spiking with hALP produced similar uE3 results to a reformulated reagent designed to address potential interference, demonstrating that this is a feasible strategy to screen for interference in a scalable manner. The vendor-provided reformulation addressed anti-ALP interference and improved the performance of the screen.

Falsely elevated serum estradiol in woman of reproductive age led to unnecessary intervention and delayed fertility opportunity: a case report and literature review

BACKGROUND

The optimal management of patients in reproductive endocrinology relies on the accuracy and validity of sex hormone assays. Endogenous or exogenous substances can compete with the analyte. This competition can result in interfering errors and falsely indicate elevated serum levels. Obvious interference in estradiol assays appears to occur rarely. Consequently, clinicians who are not familiar with the potential of interference could be misled. In addition to unnecessary investigations and interventions and severe mental stress, falsely elevated estradiol results can result in missed or delayed fertility opportunities.

CASE

A 28-year-old female with pregnancy demand was diagnosed with polycystic ovary syndrome, Hashimoto's thyroiditis and subclinical hypothyroidism. She was found to have persistently elevated levels of serum estradiol in the early follicular phase (between 527 and 642 pg/mL). Screening workup was performed for nearly 11 months to find the causes. Serum tumor biomarkers were normal. Abdominal and pelvic computed tomography were negative for adrenal or adnexal masses. A left mesosalpinx cyst and benign pathological results were achieved by laparoscopic surgery. Hormonal substances and dietary supplements were absent, as determined by dietary records. Ultrasound confirmed follicles could grow slowly and eventually ovulate. Falsely elevated estradiol levels were suspected due to the discrepancy among high estradiol levels, follicle growth and normal gonadotropin levels. Immunological interference by heterophile antibody was finally verified by two competitive chemiluminescent immunoassay platforms (estradiol levels in the early follicle phase: 619 pg/mL, Siemens ADVIA CENTAUR and 60 pg/mL, Beckman, DxI 800). Successful clinical pregnancy was eventually achieved by combining induced ovulation, ultrasound monitoring and intercourse guidance.

CONCLUSIONS

Analytical interference and laboratory error should be suspicious at first when the clinical characteristics contradict the laboratory results of serum hormones. Measuring serum estradiol with another immunoassay platform is an easy and non-time-consuming method to exclude the heterophile interfering.

Hormone Immunoassay Interference: A 2021 Update

Immunoassays are powerful qualitative and quantitative analytical techniques. Since the first description of an immunoassay method in 1959, advances have been made in assay designs and analytical characteristics, opening the door for their widespread implementation in clinical laboratories. Clinical endocrinology is closely linked to laboratory medicine because hormone quantification is important for the diagnosis, treatment, and prognosis of endocrine disorders. Several interferences in immunoassays have been identified through the years; although some are no longer encountered in daily practice, cross-reaction, heterophile antibodies, biotin, and anti-analyte antibodies still cause problems. Newer interferences are also emerging with the development of new therapies. The interfering substance may be exogenous (e.g., a drug or substance absorbed by the patient) or endogenous (e.g., antibodies produced by the patient), and the bias caused by interference can be positive or negative. The consequences of interference can be deleterious when clinicians consider erroneous results to establish a diagnosis, leading to unnecessary explorations or inappropriate treatments. Clinical laboratories and manufacturers continue to investigate methods for the detection, elimination, and prevention of interferences. However, no system is completely devoid of such incidents. In this review, we focus on the analytical interferences encountered in daily practice and possible solutions for their detection or elimination.

Alkaline phosphatase interference in immuno-enzymatic assays

Background

Alkaline phosphatase (ALP) enzymes are widely used as signal amplifiers in immunoenzymatic methods. Conditions that cause ALP elevations, such as bone or liver diseases, can cause interference in immunoenzymatic methods. We aimed to examine ALP's effect on immunoenzymatic assay by adding isolated pure ALP to the prepared serum pool.

Methods

We prepared a serum pool and divided it into 4 groups. By adding isolated pure ALP at different concentrations to each group, we obtained sample groups containing ALP enzyme at concentrations of 85 U/L, 340 U/L, 870 U/L, and 1570 U/L. 20-repetition of bhCG, ferritin, FT4, TSH, troponin I, and Vit B12 tests were performed in each group. The coefficient of variation, bias, and total error was calculated. All groups were compared by using the Friedman test for paired samples.

Results

After ALP addition, the calculated total error values of FT4, bhCG and troponin I tests were above the acceptable error limits. There were statistically significant differences in bhCG, FT4, troponin I, and Vit B12 tests compared to the baseline ALP level (P<0.0125).

Conclusions

Isolated ALP elevations can be a source of interference for immunoenzymatic methods.

Evaluation of sporadic bovine alkaline phosphatase interference in the Beckman Access unconjugated estriol (uE3) assay affecting maternal serum screening results

OBJECTIVES

Bovine alkaline phosphatase (BALP) mediated interference is a potential issue in the Beckman Access unconjugated estriol (uE3) assay. As the uE3 assay is a component of second trimester maternal serum screening characterizing this interference is essential for delivering accurate trisomy 18 and trisomy 21 risks.

DESIGN AND METHODS

Residual serum samples (n = 517) were measured by two different lots of uE3 assay. Scavenger BALP (sBALP) was added to all samples to remove potential BALP dependent interference and assessed using both lots of uE3 reagent.

RESULTS

BALP mediated interference was observed in similar frequency in both lots of reagent (~3%), although the patterns of positive and negative interference differed between the lots. Pretreatment with sBALP improved lot-to-lot comparison. The presence of BALP related interference was not related to the concentration of endogenous human alkaline phosphatase. The use of polyethylene glycol and sBALP treatment appeared to mitigate BALP mediated interference equally well, and resulted in concordance in measured uE3 concentrations between reagent lots. Additionally, heterophile antibody interference was observed in two samples affected with BALP interference, and the heterophile antibody interference was resolved by both PEG and heterophile antibody blocking reagent treatment, but not sBALP treatment. While the maternal screen numeric risk for affected samples changed, the risk classification changed from a negative to positive screen in two samples.

CONCLUSIONS

Interference in the uE3 assay has the potential to affect maternal serum risk calculations in different reagent lots, and pretreatment of samples with scavenger BALP or PEG should be considered in cases of unexplained uE3 concentrations.