A-346 Exploring Clinical Decision Making Cutoffs for the Siemens Serum HCG Assays in Pregnancy
Bibliographic record
Abstract
Abstract Background Human Chorionic Gonadotropin (HCG) is primarily produced by the trophoblast cells early after embryo implantation, making it ideal for assessing early pregnancy status. However, low levels of HCG can be secreted from the pituitary gland in non-pregnant individuals which can make interpretation challenging. In two quaternary centres in British Columbia, Canada, the total serum HCG assay on the Siemen’s Atellica platform is used. A cutoff of =2.0 IU/L, corresponding to the limit of detection (LOD), was used when the test was implemented. However, borderline elevated HCG results were noted by clinical teams, particularly in the pediatric population, raising concerns about false positives. This study explored the feasibility of using higher HCG cutoffs in assessing pregnancy status in female patients of child-bearing age, between the ages of 10 and 50. Methods A retrospective study combining laboratory data analysis and chart review was performed. From September 13, 2023 to November 13, 2024, total HCG results on the Atellica platform at two centers (one pediatric) were pulled via laboratory information systems. Results of intact HCG assays from four hospitals using the Siemens Dimensions EXL platform were also pulled. For both assays, data was filtered to select test results between 3IU/L and 6IU/L (borderline). Patients with these results were investigated by assessing whether a repeat test was done within a 6-week period. Chart review was then carried if on repeat testing there was an increase in HCG beyond 6 IU/L which could be consistent with pregnancy. Additionally, given increased concern for the pediatric population, chart review was conducted for borderline results from our pediatric centre. Results A total of 22335 HCG tests were identified, 2% of which were in the borderline range. Of these, 111 had a follow-up test within 6 weeks. Only 7 individuals had a value more than 6IU/L on repeat. On chart review, 3 pregnancies were identified but all likely had implantation occur between the two tests, meaning that the initial borderline value was still reflective of non-pregnant status. Of note, the proportion of borderline HCG values was highest at the extremes of age, with 4.9% of values in the 10-to-15-year range and 8.4% in the 45-to-50-year range. In the subset analysis from our pediatric center, a total of 614 HCG tests were identified and 27 cases with borderline results were reviewed, none of which represented pregnancy. Repeat testing rate was 41%, with some cases reflecting anxiety among both the children, families, and ordering physicians in light of a possible positive result. Conclusion Using the LOD as the cutoff for determination pregnancy status in the Atellica and Dimensions platforms produces false positive results owing to borderline values. This phenomenon was more pronounced around puberty, with chart review revealing adverse emotional impacts and unnecessary healthcare utilization. Meanwhile, our analysis revealed that treating these borderline values as negative results would not have resulted in any pregnancies being missed. These findings support adoption of a higher threshold detection of HCG though further studies are needed to define this threshold.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.016 | 0.480 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".