Thyroglobulin Antibody Screen Prior to Mass Spectrometry Provides Measurable Cost Savings and Optimal Laboratory Utilization

Indoleamine 2,3-Dioxygenase Immune Status as a Potential Biomarker of Radioiodine Efficacy for Advanced Distant Metastatic Differentiated Thyroid Cancer

Purpose

Host immunity influences the impact of cancer therapy but the effect of immune status in radioiodine (RAI)-treated differentiated thyroid cancer (DTC) remains obscure. Here we investigated indoleamine 2,3-dioxygenase (IDO) activity as a biomarker of response to RAI in patients with distant metastatic DTC (dmDTC).

Methods

Patients with dmDTC receiving RAI were evaluated for serum IDO activity (kynurenine and kynurenine:tryptophan ratio) at baseline and 3 months after RAI. The optimal cut-off value for these biomarkers to predict response was established by receiver operating characteristic analysis. The relationship between disease outcomes, overall survival (OS) and progression-free survival (PFS), and IDO activity levels was studied.

Results

Higher baseline kynurenine:tryptophan ratio (>2.46) was correlated with poorer RAI response as well as shorter median PFS (45 mo versus not reached, p=0.002) and OS (78 mo versus not reached, p=0.035). High baseline kynurenine:tryptophan ratio was also correlated with a reduced number of tumor-infiltrating lymphocytes. Higher post/pre-kynurenine ratio (>1.69) was associated with survival endpoints: shorter median PFS (48 mo versus not reached, p=0.002) and OS (68 mo versus not reached, p=0.010). Favorable baseline and favorable change corresponded with better PFS and OS.

Conclusions

Our results suggest that RAI also alters IDO activity in dmDTC patients. IDO activity could predict progression and survival outcomes for advanced dmDTC patients. Serum IDO biomarker levels could be used to select dmDTC likely to benefit from RAI therapy, although further studies are necessary.

A Novel Thyroglobulin Immunoassay Using the Specimen-Pretreatment Process Improves the Accuracy of Thyroglobulin Measurements in Anti-Thyroglobulin Positive Specimens

BACKGROUND

Recently, second-generation thyroglobulin (Tg) sandwich immunoassays have been used in clinical laboratories to measure the serum Tg levels, which is a tumor marker used to monitor postoperative patients with differentiated thyroid cancers. However, these immunoassays are often subject to Tg autoantibody (TgAb) interference. TgAb interference is inevitable for almost all Tg immunoassays, resulting in unreliable Tg measurement values of TgAb-positive samples.

METHODS

To address TgAb interference, we have developed a novel immunoassay based on a fully automated chemiluminescent enzyme immunoassay system using the effective specimen-pretreatment process to inactivate TgAb in blood and evaluated its assay performance.

RESULTS

The developed assay was traceable to BCR457 IRMM reference material with a limit of quantification of 0.03 ng/mL. The pretreatment process inactivated almost all TgAb in specimens and allowed accurate Tg measurements in TgAb-positive samples in which TgAb interference was observed using the immunoassays. Size-exclusion chromatography analysis of immunoreactive Tg molecule in a TgAb-positive serum verified disruption of the Tg-TgAb immune complex by the pretreatment process. Good correlation of Tg values in TgAb-negative specimens was observed between the new Tg immunoassay and the second-generation sandwich immunoassays. However, there were numerous discrepant samples on bias plots between the new Tg immunoassay and the second-generation sandwich immunoassays for TgAb-positive specimens.

CONCLUSIONS

This study indicates the new Tg immunoassay with the specimen-pretreatment process is both robust and free from interference by TgAb. Thus, this novel assay is superior to second-generation sandwich immunoassays and gives accurate Tg concentrations even for TgAb-positive cases.

Lowering the Bar for Mass Spectrometry: A Comparison between Immunoassay and Rapid Time-of-Flight for Presumptive Screening of Drugs in Urine

BACKGROUND

Immunoassay-based techniques and creatinine quantification have historically been the methods of choice for urine drug screening. Positive presumptive drug screen results are reflexed to more specific, confirmatory testing using gas or liquid chromatography coupled to mass spectrometry. False positives and false negatives with immunoassay techniques are common problems that have substantial down-stream consequences for patient care, laboratory operations, and total costs.

METHODS

The final workflow included rapid enzymatic hydrolysis, rapid liquid chromatographic methods, and time-of-flight mass spectrometry for detection. In total, 84 drugs and metabolites were included and reported qualitatively using 11 isotopically labeled internal standards selected to represent compound classes, retention time, and expected abundances to control for method inefficiencies and matrix suppression/enhancement. The method performance validation included 420 individual urine specimens.

RESULTS

Of the 420 samples screened by immunoassay, 117 failed to confirm by mass spectrometry and were immunoassay false positives. None of these 117 samples screened positive on the liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) assay. The LC-TOF-MS method failed to detect 1 sample in each of the following classes: buprenorphine, ethanol markers, and opiates owing to concentrations below the established cutoffs. Out of 579 samples, 275 (47.4%) screened positive by LC-TOF-MS for nicotine and at least 2 of its metabolites. Quantitative creatinine comparison to an existing Jaffe method yielded a slope of 0.91 and a correlation coefficient of 0.96.

CONCLUSIONS

We investigated whether immunoassay-based drug screening and creatinine quantification could be sufficiently replaced by a rapid LC-TOF-MS screen with higher specificity and accuracy than existing methods. The LC-LC-TOF-MS method is a sensitive and more specific way to screen for drugs, providing creatinine quantification and potential novel specimen validity testing with the inclusion of nicotine metabolites.