Correlation does not imply agreement: A cautionary tale for researchers and reviewers

Lateral flow test versus enzyme-linked immunosorbent assay to measure infliximab trough concentrations: A head-to-head comparison

OBJECTIVES

Infliximab is an antitumour necrosis factor agent used to treat inflammatory bowel disease (IBD). Measurement of infliximab trough concentrations (C-troughs) are used to optimize drug exposure and improve outcomes. Currently, enzyme-linked immunosorbent assays (ELISAs) are used predominantly for this purpose. Novel lateral flow immunoassays provide a rapid result.

METHODS

We collected 100 paired serum samples of adolescents and young adults with IBD, who were treated with infliximab maintenance infusions. C-troughs were measured with the Quantum Blue® lateral flow test (QB) with ELISA. Results were categorized as low-range (mean C-trough ≤5 µg/mL) or high-range (>5 µg/mL). A Bland-Altman plot was created with limits of clinical acceptability set at ≤2 µg/mL for low-range and ≤40% for high-range C-troughs. A concordance matrix was created to evaluate the C-trough-based clinical scenario (whether or not to escalate infliximab) using a cutoff value of 5 µg/mL.

RESULTS

Agreement between QB and ELISA was good (intraclass correlation coefficient: 0.85). In the low-range, 90% (95% confidence interval [CI]: 79-96) of measurements were within the limits of clinical acceptability. In the high-range this was 67% (95% CI: 53-79). QB provided higher results than ELISA. The concordance matrix showed 81% agreement (95% CI: 72-88, κ: 0.62).

CONCLUSIONS

Lateral flow- and ELISA-based infliximab C-trough measurements were in agreement. The swift establishment of infliximab C-troughs matters for patients experiencing increased disease activity. In the event of a low C-trough, prompt dose escalation can be initiated.

From a glimpse into the key aspects of calibration and correlation to their practical considerations in chemical analysis

In this tutorial review, we provide a guiding reference on the good practice in building calibration and correlation experiments, and we explain how the results should be evaluated and interpreted. The review centers on calibration experiments where the relationship between response and concentration is expected to be linear, although certain of the described principles of good practice can be applied to non-linear systems, as well. Furthermore, it gives prominence to the meaning and correct interpretation of some of the statistical terms commonly associated with calibration and regression. To reach a mutual understanding in this significant field, we present, through a practical example, a step-by-step procedure, which deals with typical challenges related to linearity and outlier assessment, calculation of the associated error of the predicted concentration, and limits of detection. The utilization of regression lines to compare analytical methods is also elaborated. The results of regression and correlation data are acquired by implementing the Excel spreadsheet of Microsoft, being perhaps one of the most widely used user-friendly software in education and research.

Novel evaluation approach for molecular signature-based deconvolution methods

The tumoral immune microenvironment (TIME) plays a key role in prognosis, therapeutic approach and pathophysiological understanding over oncological processes. Several computational immune cell-type deconvolution methods (DM), supported by diverse molecular signatures (MS), have been developed to uncover such TIME interplay from RNA-seq tumor biopsies. MS-DM pairs were benchmarked against each other by means of different metrics, such as Pearson's correlation, R2 and RMSE, but these only evaluate the linear association of the estimated proportion related to the expected one, missing the analysis of prediction-dependent bias trends and cell identification accuracy. We present a novel protocol composed of four tests allowing appropriate evaluation of the cell type identification performance and proportion prediction accuracy of molecular signature-deconvolution method pair by means of certainty and confidence cell-type identification scores (F1-score, distance to the optimal point and error rates) as well the Bland-Altman method for error-trend analysis. Our protocol was used to benchmark six state-of-the-art DMs (CIBERSORTx, DCQ, DeconRNASeq, EPIC, MIXTURE and quanTIseq) paired to five murine tissue-specific MSs, revealing a systematic overestimation of the number of different cell types across almost all methods.

Accuracy and precision of contrast enhanced mammography versus MRI for predicting breast cancer size: how "good" are they really?

OBJECTIVE

To evaluate and compare the accuracy and precision of contrast-enhanced mammography (CEM) vs MRI to predict the size of biopsy-proven invasive breast cancer.

METHODS

Prospective study, 59 women with invasive breast cancer on needle biopsy underwent CEM and breast MRI. Two breast radiologists read each patient's study, with access limited to one modality. CEM lesion size was measured using low-energy and recombined images and on MRI, the first post-contrast series. Extent of abnormality per quadrant was measured for multifocal lesions. Reference standards were size of largest invasive malignant lesion, invasive (PathInvasive) and whole (PathTotal). Pre-defined clinical concordance ±10 mm.

RESULTS

Mean patient age 56 years, 42 (71%) asymptomatic. Lesions were invasive ductal carcinoma 40 (68%) with ductal carcinoma in situ (31/40) in 78%, multifocal in 12 (20%). Median lesion size was 17 mm (invasive) and 27 mm (total), range (5-125 mm). Lin's concordance correlation coefficients for PathTotal 0.75 (95% CI 0.6, 0.84) and 0.71 (95% CI 0.56, 0.82) for MRI and contrast-enhanced spectral mammography (CESM) respectively. Mean difference for total size, 3% underestimated and 4% overestimated, and for invasive 41% and 50% overestimate on MRI and CESM respectively. LOAs for PathTotal varied from 60% under to a 2.4 or almost threefold over estimation. MRI was concordant with PathTotal in 36 (64%) cases compared with 32 (57%) for CESM. Both modalities concordant in 26 (46%) cases respectively.

CONCLUSION

Neither CEM nor MRI have sufficient accuracy to direct changes in planned treatment without needle biopsy confirmation.

ADVANCES IN KNOWLEDGE

Despite small mean differences in lesion size estimates using CEM or MRI, the 95% limits of agreement do not meet clinically acceptable levels.