Validation of blood-based assays using dried blood spots for use in large population studies

Cumulative Physiologic Dysfunction and Pregnancy: Characterization and Association with Birth Outcomes

Objective To characterize cumulative physiologic dysfunction (CPD) in pregnancy as a measure of the biological effects of chronic stress and to examine its associations with gestational age and birth weight. Methods Women ≤28 weeks gestation were enrolled from obstetric clinics in Rochester, NY and followed through their delivery. CPD parameters included total cholesterol, Interleukin 6 (IL-6), high sensitivity-C-reactive protein (hs-CRP), systolic and diastolic blood pressure, body mass index at <14 weeks gestation, glucose tolerance, and urinary albumin collected in the third trimester. Linear regression was used to estimate the association between physiologic dysfunction and birth weight and gestational age, respectively (N = 111). Results CPD scores ranged from 0 to 6, out of a total of 8 parameters (Mean 2.09; SD = 1.42). Three-fourths of the participants had a CPD score of 3.0 or lower. The mean birth weight was 3397 g (SD = 522.89), and the mean gestational age was 39.64 weeks (SD = 1.08). CPD was not significantly associated with either birth weight or gestational age (p = 0.42 and p = 0.44, respectively). Conclusion CPD measured at >28 weeks was not associated with birth weight or gestational age. Refinement of a CPD score for pregnancy is needed, taking into consideration both the component parameters and clinical and pre-clinical cut-points for risk scoring.

HPLC-based Measurement of Glycated Hemoglobin using Dried Blood Spots Collected under Adverse Field Conditions

Glycated hemoglobin (HbA1c) measured using high-performance liquid chromatography (HPLC) assays with venous blood and dried blood spots (DBS) are compared for 143 paired samples collected in Aceh, Indonesia. Relative to gold-standard venous-blood values, DBS-based values reported by the HPLC are systematically upward biased for HbA1c<8% and the fraction diabetic (HbA1c ≥ 6.5%) is overstated almost five-fold. Inspection of chromatograms from DBS assays indicates the % glycosylated calculated by the HPLC excludes part of the hemoglobin A which is misidentified as a hemoglobin variant. Taking this into account, unbiased DBS-based values are computed using data from the machine-generated chromatograms. When the DBS are collected in a clinic-like setting, under controlled humidity/temperature conditions, the recalculated values are almost identical to venous-based values. When DBS are collected under field conditions, the recalculated values are unbiased, but only about half the HbA1c values are measured reliably, calling into question the validity of the other half. The results suggest that collection conditions, particularly humidity, affect the quality of the DBS-based measures. Cross-validating DBS-based HbA1c values with venous samples collected under exactly the same environmental conditions is a prudent investment in population-based studies.

Neighborhood cohesion, neighborhood disorder, and cardiometabolic risk

Perceptions of neighborhood disorder (trash, vandalism) and cohesion (neighbors trust one another) are related to residents' health. Affective and behavioral factors have been identified, but often in studies using geographically select samples. We use a nationally representative sample (n = 9032) of United States older adults from the Health and Retirement Study to examine cardiometabolic risk in relation to perceptions of neighborhood cohesion and disorder. Lower cohesion is significantly related to greater cardiometabolic risk in 2006/2008 and predicts greater risk four years later (2010/2012). The longitudinal relation is partially accounted for by anxiety and physical activity.

Comparing identified and statistically significant lipids and polar metabolites in 15-year old serum and dried blood spot samples for longitudinal studies

RATIONALE

The use of dried blood spots (DBS) has many advantages over traditional plasma and serum samples such as the smaller blood volume required, storage at room temperature, and ability to sample in remote locations. However, understanding the robustness of different analytes in DBS samples is essential, especially in older samples collected for longitudinal studies.

METHODS

Here we analyzed the stability of polar metabolites and lipids in DBS samples collected in 2000-2001 and stored at room temperature. The identified and statistically significant molecules were then compared to matched serum samples stored at -80°C to determine if the DBS samples could be effectively used in a longitudinal study following metabolic disease.

RESULTS

A total of 400 polar metabolites and lipids were identified in the serum and DBS samples using gas chromatograph/mass spectrometry (GC/MS), liquid chromatography (LC)/MS, and LC/ion mobility spectrometry-MS (LC/IMS-MS). The identified polar metabolites overlapped well between the sample types, though only one statistically significant metabolite was conserved in a case-control study of older diabetic males with low amounts of high-density lipoproteins and high body mass indices, triacylglycerides and glucose levels when compared to non-diabetic patients with normal levels, indicating that degradation in the DBS samples affects polar metabolite quantitation. Differences in the lipid identifications indicated that some oxidation occurs in the DBS samples. However, 36 statistically significant lipids correlated in both sample types.

CONCLUSIONS

The difference in the number of statistically significant polar metabolites and lipids indicated that the lipids did not degrade to as great of a degree as the polar metabolites in the DBS samples and lipid quantitation was still possible. Copyright © 2016 John Wiley & Sons, Ltd.

Enzyme-Linked Immunoassay-Based Quantitative Measurement of Apolipoprotein B (ApoB) in Dried Blood Spots, a Biomarker of Cardiovascular Disease Risk

Apolipoprotein B (ApoB) is a strong predictor of cardiovascular disease, which remains the leading cause of mortality in both higher and lower income countries. Here, we adapted an enzyme-linked immunosorbent assay (ELISA) development kit for quantitative determination of ApoB levels in serum and plasma for use with dried blood spots (DBS). After confirming the dilution linearity of the assay for DBS, we measured ApoB in 208 venous DBS samples. Then, using Passing-Bablok regression analysis and Spearman rank correlation analysis, we evaluated the correspondence in ApoB values between matched plasma and finger-prick DBS samples from 40 individuals who had ApoB values spanning the range of ApoB values observed in the 208 vDBS samples. We also evaluated assay precision and recovery, the effects of hematocrit, number of freeze-thaw cycles, and different storage temperatures on ApoB levels in DBS. There was a strong, significant correlation between plasma and DBS ApoB levels with little bias. Assay precision and recovery were within the range recommended by the U.S. government's industry guidelines for bioanalytical assay validation. The assay was not affected by the DBS matrix or physiological hematocrit levels. This DBS-based ELISA assay will facilitate population-scale assessment of cardiovascular risk in previously unexplored populations.

"Inflammaging" and Estradiol among Older U.S. Women: A Nationally Representative Longitudinal Study

Despite accumulating small-sample and clinical evidence on "inflammaging," no population-representative longitudinal studies have specifically examined women's late-life inflammation trends. While a range of studies indicates estradiol's immunomodulation role, evidence is contradictory on whether its effects are pro- or antiinflammatory among older women. Using longitudinal data from the first two waves of the National Social Life, Health and Aging Project-a national probability sample of older U.S. adults aged 57 to 85 years at baseline-this study began to fill these gaps. Findings suggested rather than being a lifelong process, older women's inflammaging may have a biological window that closes with senescence. Moreover, their endogenous estradiol plays a proinflammatory rather than immunoprotective role. Nor does this sex steroid modulate age effects on women's inflammation. More sex-specific basic research is needed on causal mechanisms underlying women's late-life inflammaging patterns.

Novel applications for a noninvasive sampling method of the nasal mucosa

Reliable methods for sampling the nasal mucosa provide clinical researchers with key information regarding respiratory biomarkers of exposure and disease. For quick and noninvasive sampling of the nasal mucosa, nasal lavage (NL) collection has been widely used as a clinical tool; however, limitations including volume variability, sample dilution, and storage prevent NL collection from being used in nonlaboratory settings and analysis of low abundance biomarkers. In this study, we optimize and validate a novel methodology using absorbent Leukosorb paper cut to fit the nasal passage to extract epithelial lining fluid (ELF) from the nasal mucosa. The ELF sampling method limits the dilution of soluble mediators, allowing quantification of both high- and low-abundance soluble biomarkers such as IL-1β, IL-8, IL-6, interferon gamma-induced protein 10 (IP-10), and neutrophil elastase. Additionally, we demonstrate that this method can successfully detect the presence of respiratory pathogens such as influenza virus and markers of antibiotic-resistant bacteria in the nasal mucosa. Efficacy of ELF collection by this method is not diminished in consecutive-day sampling, and percent recovery of both recombinant IL-8 and soluble mediators are not changed despite freezing or room temperature storage for 24 h. Our results indicate that ELF collection using Leukosorb paper sampling of ELF provides a sensitive, easy-to-use, and reproducible methodology to collect concentrated amounts of soluble biomarkers from the nasal mucosa. Moreover, the methodology described herein improves upon the standard NL collection method and provides researchers with a novel tool to assess changes in nasal mucosal host defense status.

Innovations in health and demographic surveillance systems to establish the causal impacts of HIV policies

PURPOSE OF REVIEW

Health and demographic surveillance systems (HDSS), in conjunction with HIV treatment cohorts, have made important contributions to our understanding of the impact of HIV treatment and treatment-related interventions in sub-Saharan Africa. The purpose of this review is to describe and discuss innovations in data collection and data linkage that will create new opportunities to establish the impacts of HIV treatment, as well as policies affecting the treatment cascade, on population health and economic and social outcomes.

RECENT FINDINGS

Novel approaches to routine collection of biomarkers, behavioural data, spatial data, social network information, migration events and mobile phone records can significantly strengthen the potential of HDSS to generate exposure and outcome data for causal analysis of HIV treatment impact and policies affecting the HIV treatment cascade. Additionally, by linking HDSS data to health service administration, education and welfare service records, researchers can substantially broaden opportunities to establish how HIV treatment affects health and economic outcomes when delivered through public sector health systems and at scale.

SUMMARY

As the HIV treatment scaleup in sub-Saharan Africa enters its second decade, it is becoming increasingly important to understand the long-term causal impacts of large-scale HIV treatment and related policies on broader population health outcomes, such as noncommunicable diseases, as well as on economic and social outcomes, such as family welfare and children's educational attainment. By collecting novel data and linking existing data to public sector records, HDSS can create near-unique opportunities to contribute to this research agenda.

Socioeconomic status, daily affective and social experiences, and inflammation during adolescence

OBJECTIVE

To assess the relation between socioeconomic status (SES) and inflammation during adolescence and determine whether daily affective and social experiences across a 15-day period mediate this relation.

METHODS

Adolescents (n = 316) completed daily diary reports of positive affect, negative affect, and negative social interactions for 15 days and provided whole blood spot samples for the assessment of C-reactive protein (CRP). Parents provided information on SES, including the highest level of education they and their spouses completed and household income.

RESULTS

Lower parent education was associated with higher levels of adolescent CRP, controlling for age, sex, ethnicity, and body mass index (β = -.12, p = .031). Mean daily positive affect, negative affect, and negative social interactions were examined as potential mediators of this association. In these models, parent education was no longer associated with adolescent CRP (β = -.09, p = .12), and only positive affect was related to CRP (β = -.12, p = .025). Bootstrapping confirmed the mediating role of positive affect (indirect effect = -0.015, 95% confidence interval = -0.038 to -0.002).

CONCLUSIONS

Adolescents with less educated parents tended to have higher levels of CRP, which may be explained by their lower levels of positive affect. Findings suggest that a lack of positive affect may be a pathway by which SES confers early risk for poor health in adulthood. It is possible that adolescents who display positive affect during daily life in circumstances of relatively adverse socioeconomic circumstances may have better health outcomes related to lower inflammatory factors.

Validation of Biomarkers of CVD Risk from Dried Blood Spots in Community-Based Research: Methodologies and Study-Specific Serum Equivalencies

Dried blood spot (DBS) methodology offers significant advantages over venipuncture in studies of vulnerable populations or large-scale studies, including reduced participant burden and higher response rates. Uncertainty about the validity of cardiovascular disease (CVD) risk biomarkers remains a barrier to wide-scale use. We determined the validity of DBS-derived biomarkers of CVD risk versus gold-standard assessments, and study-specific, serum-equivalency values for clinical relevance of DBS-derived values. Concurrent venipuncture serum and DBS samples (n = 150 adults) were assayed in Clinical Laboratory Improvement Amendments-certified and DBS laboratories, respectively. Time controls of DBS standard samples were assayed single-blind along with test samples. Linear regression analyses evaluated DBS-to-serum equivalency values; agreement and bias were assessed via Bland-Altman plots. Linear regressions of venipuncture values on DBS-to-serum equivalencies provided R(2) values for total cholesterol, high-density lipoprotein cholesterol (HDL-C), and C-reactive protein (CRP) of 0.484, 0.118, and 0.666, respectively. Bland-Altman plots revealed minimal systematic bias between DBS-to-serum and venipuncture values; precision worsened at higher mean values of CRP. Time controls revealed little degradation or change in analyte values for HDL-C and CRP over 30 weeks. We concluded that DBS-assessed biomarkers represent a valid alternative to venipuncture assessments. Large studies using DBS should include study-specific serum-equivalency determinations to optimize individual-level sensitivity, the viability of detecting intervention effects, and generalizability in community-level primary prevention interventions.

Blood Substrate Collection and Handling Procedures under Pseudo-Field Conditions: Evaluation of Suitability for Inflammatory Biomarker Measurement

Routine incorporation of blood-based biomarker measurements in population studies has been hampered by challenges in obtaining samples suitable for biomarker assessment outside of laboratory settings. Here, we assessed the suitability of venous blood left unprocessed for 4, 24, or 48 hours post-collection at either room temperature or 4°C for quantification of two biomarkers, Interleukin-6 (IL-6) and C-reactive protein (CRP). Blood samples were collected in both K2EDTA tubes and a dedicated plasma-preservation tube, P100. Dried blood spot (DBS) samples from the same subjects were also collected in order to compare delayed-processing plasma performance against a popular alternative collection method. We found that K2EDTA mean plasma concentrations of both IL-6 and CRP were not significantly different from concentrations in plasma processed immediately; this was observed for tubes stored up to 48 hours pre-processing at either temperature. Concentrations of IL-6 measured in P100 tubes showed significant time-dependent increases when stored at room temperature; otherwise, levels of IL-6 and CRP were similar to those found in samples processed immediately. Levels of CRP in DBS were correlated with plasma CRP levels, even when pre-processed blood was stored for up to 48 hours. These data indicate that plasma is suitable for IL-6 and CRP estimation under data collection conditions that involve processing delays.

Validation and modification of dried blood spot-based glycosylated hemoglobin assay for the longitudinal aging study in India

OBJECTIVES

This study aims to validate a modified dried blood spot (DBS)-based glycosylated hemoglobin (HbA1c) assay protocol, after a pretest in India showed poor correlation between the original DBS-based protocol and venous results.

METHODS

The original protocol was tested on different chemistry analyzers and then simplified at the University of Washington (UW). A second pretest was conducted in India to validate the modified assay protocol, using 44 quality control specimens.

RESULTS

Data from UW indicated that, using the original protocol, the correlation coefficients between DBS and venous results were above 0.98 on both Bio-Rad and Olympus chemistry analyzers. The protocol worked equally well on filter paper, with or without pre-treatment, and when the recommended amount of blood spot material, or less, was used. A second pretest of the modified protocol confirmed that DBS-based levels from both Olympus and Roche chemistry analyzers were well correlated with DBS results from UW (correlation coefficients were above 0.96), as well as with venous values (correlation coefficients were above 0.94).

CONCLUSIONS

The DBS-based HbA1c values are highly correlated with venous results. The pre-treatment of filter paper does not appear to be necessary. The poor results from the first pretest are probably due to factors unrelated to the protocol, such as problems with the chemistry analyzer or assay reagents.