Indirect free thyroxine (FT4) immunoassay results in pregnancy interpreted in the context of trimester-specific reference intervals may provide a practical and viable alternative to total T4 (TT4) or free thyroxine index (FTI) (Clin Chem 2021;

Professional guidelines from the American Thyroid Association and Endocrine Society discourage the use of indirect immunoassays for measuring FT4 in pregnancy when interpreted in the context of the reference interval used outside of pregnancy (NP interval). Instead, the guidelines suggest interpreting TT4 in the context of 1.5-times the NP interval during the second or third trimester or calculating the FTI with a direct method involving measurement of free hormone after a physical separation step. If there is no alternative to a FT4 immunoassay, labs should use trimester-specific reference intervals. These recommendations are based on research that describes the limitations of indirect FT4 immunoassays without using a comparison against a reference method.

To evaluate the recommendations’ impact on classifying thyroid status in apparently euthyroid pregnant patients, the researchers evaluated clinical samples from 147 nonpregnant women of childbearing age and a total of 480 pregnant individuals in all trimesters using both indirect immunoassay and direct FT4, thyroid-stimulating hormone (TSH), TT4, and T-uptake. The researchers made split-sample comparisons of FT4 as measured and equilibrium dialysis.

FT4 decreased with advancing gestational age, as measured by both immunoassay and equilibrium dialysis. TSH declined during the first trimester, remained constant in the second, and increased throughout the third, peaking just before delivery. Interpretation of TT4 concentrations using 1.5-times the NP interval classified 13.6% of first trimester specimens below the lower reference limit, despite TSH concentrations within trimester-specific reference intervals. Five FTI results from the 480 pregnant individuals (about 1.0%) fell outside the manufacturer’s reference interval.

These findings underscore the need to establish gestational age-specific reference intervals for all assays used to assess thyroid function, the researchers note.

Timing of SARS-CoV-2 Serology Tests May Matter

While antibody response to a SARS-CoV-2 infection is clinically detectable many months after an infection, recent research suggests testing too soon may lead to an incorrect assessment of immune response (JAMA Network Open 2021; doi:10.1001/jamanetworkopen. 2021.0337).

Using clinical data from the University of California Health (UC Health) system, researchers examined three types of clinical immunoglobulin G (IgG) measurements in patients with real-time reverse transcription-polymerase chain reaction (RT-PCR) confirmation of SARS-CoV-2 infection. The investigators calculated antibody test sensitivity in 7-day increments from the date of the positive RT-PCR test and used the t-test to compare sensitivity by patient-reported sex and variance analysis to compare sensitivity by assay types and age.

Among the 277,567 UC Health system patients tested via RT-PCR for SARS-CoV-2, 14,290 had antibody tests. Of 10,065 patients with positive RT-PCR results for SARS-CoV-2, 4.8% had subsequent SARS-CoV-2 antibody testing a median of 34 days later.

Serology tests were positive in 75.1% of patients, but antibody response varied by test timing. Serology tests conducted closer to a patient’s positive RT-PCR results were more likely to have negative results than those done later. The likelihood of positive SARS-CoV-2 antibody test results increased with longer intervals between the positive RT-PCR result and the antibody test, with sensitivity reaching 0.75 at 112 days after the positive RT-PCR result.

Sensitivity varied by test type, sex, and age. Maximum sensitivity for the Beckman Coulter SARS-CoV-2 IgG test, Liaison SARS-CoV-2 S1/S2 IgG test, and DZ-Lite SARS-CoV-2 IgG CLIA kit was 0.84, 0.78, and 0.67, respectively. Serology sensitivity was significantly higher among males than females. It was highest at 126 days after positive RT-PCR results for males, versus 133 days afterwards for females. By age group, sensitivity was highest among patients 50–59 years old. Only pairwise comparisons of antibody test sensitivities between the youngest and oldest groups and patients aged 40–49, versus those aged 50–59, differed significantly.

The researchers suggested a larger study to validate their findings.

Useful Breast Cancer Panel Genes Suggested

A recent study defines the genes that are most clinically useful in panels that predict breast cancer risk and provides estimates of risks associated with protein-truncating variants. This information that may guide clinical reporting of panel testing results and genetic counseling (N Engl J Med 2021;384:428-39).

As sequencing becomes more affordable, making the use of larger panels of genes possible, the researchers sought to establish stronger associations of some genes with cancer and more accurate estimates of particular variants’ pathogenicity. Using a panel of 34 commonly accepted susceptibility genes, the authors sequenced samples from 60,466 women with breast cancer and 53,461 controls. In separate analyses for protein-truncating variants and rare missense variants in the 34 genes, the authors estimated odds ratios for both breast cancer overall and tumor subtypes. They also evaluated missense-variant associations according to domain and pathogenicity classification.

Protein-truncating variants in 5 genes—ATM, BRCA1, BRCA2, CHEK2, and PALB2—were associated with a risk of breast cancer overall with a P value of less than 0.0001. Protein-truncating variants in 4 other genes—BARD1, RAD51C, RAD51D, and TP53—were associated with a risk of breast cancer overall with a P value of less than 0.05 and a Bayesian false-discovery probability of less than 0.05. For protein-truncating variants in 19 of the remaining 25 genes, the upper limit of the 95% confidence interval of the odds ratio for breast cancer overall was less than 2.0.

For protein-truncating variants in ATM and CHEK2, odds ratios were higher for estrogen receptor (ER)-positive disease than for ER-negative disease. For protein-truncating variants in BARD1, BRCA1, BRCA2, PALB2, RAD51C, and RAD51D, odds ratios were higher for ER-negative disease than for ER-positive disease. In aggregate, rare missense variants in ATM, CHEK2, and TP53 were associated with a risk of breast cancer overall with a P value of less than 0.001. For BRCA1, BRCA2, and TP53, missense variants in aggregate that standard criteria would deem pathogenic were associated with a risk of breast cancer overall, with the risk being similar to that of protein-truncating variants.