The development of blood-based biomarkers of Alzheimer’s disease (AD) pathology as tools for screening the general population, and as the first step in a multistep process to determine which non-demented individuals are at greatest risk of developing AD dementia, is essential. Proteins that are reflective of AD pathology, such as amyloid beta 42 (Aβ₄₂), tau proteins [total tau (T-tau) and phosphorylated tau (P-tau)], and neurofilament light chain (NfL), are detectable in the blood. However, a major challenge in measuring these blood-based proteins is that their concentrations are much lower in plasma or serum than in the cerebrospinal fluid. Single molecule array (SiMoA) is an ultrasensitive technology that can detect proteins in blood at sub-femtomolar concentrations (i.e., 10⁻¹⁶ M). In this review, we focus on the utility of SiMoA assays for the measurement of plasma or serum Aβ₄₂, P-tau, T-tau, and NfL levels and discuss future directions.

Inaccuracy of laboratory medicine diagnostic tests may be associated with ingestion of over-the-counter vitamin and herbal supplements.^1,2 One such example is interference associated with biotin. Biotin (vitamin B7), a water-soluble vitamin found in meat, fish, eggs, and dairy,³ serves as a catalyst for carboxylase enzymes important in macronutrient metabolism.⁴ Biotin supplements, especially very large doses (eg, 10-15 mg/d, or 333-fold greater than the dietary recommendation of 30 µg/d)⁵ have become popular for presumptive health benefits such as stimulating hair growth and treating certain medical conditions including biotinidase deficiency, diabetes, lipid disorders, and diabetic peripheral neuropathy.^6-9 Ingestion of up to 300 mg/d may be beneficial for multiple sclerosis.^10,11 Taking high-doses of biotin may result in inaccurate laboratory results because biotin is commonly used, in the form of biotinylated antibodies or analogues, as a critical component in immunoassays. These assays exploit the strong, stable, and specific binding between biotin and streptavidin to amplify the assay sensitivity for detecting low analyte levels.^12,13 Excessive biotin in a blood sample can compete with biotinylated components in the assay, potentially falsely decreasing results in sandwich immunoassays or falsely increasing results in competitive immunoassays (eFigures 1 and 2 in the Supplement).¹⁴

Carbonylation is a highly prevalent protein modification in skeletal muscle mitochondria, possibly contributing to its functional decline with age. Using quantitative proteomics, we identified mitochondrial proteins susceptible to carbonylation in a muscle type (slow- vs fast-twitch)-dependent and age-dependent manner from Fischer 344 rat skeletal muscle. Fast-twitch muscle contained twice as many carbonylated mitochondrial proteins than did slow-twitch muscle, with 22 proteins showing significant changes in carbonylation state with age, the majority of these increasing in their amount of carbonylation. Ingenuity pathway analysis revealed that these proteins belong to functional classes and pathways known to be impaired in muscle aging, including cellular function and maintenance, fatty acid metabolism, and citrate cycle. Although our studies do not conclusively link protein carbonylation to these functional changes in aging muscle, they provide a unique catalogue of promising protein targets deserving further investigation because of their potential role in aging muscle decline.

Background: Laboratory tests that use streptavidin–biotin binding mechanisms have the potential to be affected by high circulating biotin concentrations, which would produce positive and negative interference in biotinylated competitive and noncompetitive (sandwich) immunoassays, respectively. Consumption of high-dose biotin supplements for cosmetic or health-related reasons has drawn attention to biotin interference in clinical laboratory tests. Case reports and in vivo studies show that ingestion of supplemental biotin can cause clinically significant errors in select biotinylated immunoassays. Content: This AACC Academy document is intended to provide guidance to laboratorians and clinicians for preventing, identifying, and dealing with biotin interference. In vivo and in vitro spiking studies have demonstrated that biotin concentrations required to cause interference vary by test and by manufacturer. This document includes discussion of biotin’s mechanisms for interference in immunoassays, pharmacokinetics, and results of in vitro and in vivo studies and cites examples of assays known to be affected by high biotin concentrations. This document also provides guidance recommendations intended to assist laboratories and clinicians in identifying and addressing biotin interference in laboratory testing. Summary: The recent increase in the use of high-dose biotin supplements requires laboratorians and clinicians to be mindful of the potential for biotin interference in biotinylated immunoassay-based laboratory tests. Laboratories, clinicians, regulators, and patients should work together to ensure accurate laboratory results. Laboratories have several options for identifying suspected biotin interference in specimens. Alternatively, the relatively fast elimination of biotin allows the potential for rapid follow-up specimen analysis if necessary.