Spot ferritin assay for serum samples dried on filter paper

Dried blood spot compared to plasma measurements of blood-based biomarkers of brain injury in neonatal encephalopathy

BACKGROUND

Data correlating dried blood spots (DBS) and plasma concentrations for neonatal biomarkers of brain injury are lacking. We hypothesized that candidate biomarker levels determined from DBS can serve as a reliable surrogate for plasma levels.

METHODS

In the context of a phase II multi-center trial evaluating erythropoietin for neuroprotection in neonatal encephalopathy (NE), DBS were collected at enrollment ( < 24 h), day 2, 4, and 5. Plasma was collected with the first and last DBS. The relationship between paired DBS-plasma determinations of brain-specific proteins and cytokines was assessed by correlation and Bland-Altman analyses. For analytes with consistent DBS-plasma associations, DBS-derived biomarker levels were related to brain injury by MRI and 1-year outcomes.

RESULTS

We enrolled 50 newborns with NE. While S100B protein, tumor necrosis factor α, interleukin (IL)1 β, IL-6, IL-8 demonstrated significant DBS-plasma correlations, Bland-Altman plots demonstrated that the methods are not interchangeable, with a 2 to 4-fold error between measurements. No significant relationships were found between DBS levels of TNFα, IL-6, and IL-8 and outcomes.

CONCLUSION

Further work is needed to optimize elution and assay methods before using DBS specimens as a reliable surrogate for plasma levels of candidate brain injury biomarkers in NE.

Development and validation of assay protocols for use with dried blood spot samples

Dried blood spots (DBS)--drops of capillary whole blood collected from finger stick--represent a minimally invasive alternative to venipuncture that facilitates the collection of blood samples from research participants in naturalistic, field-based research settings. But the number of validated assays for quantifying biomarkers in DBS samples is relatively low in comparison with serum or plasma. The objective of this review is to discuss the advantages and disadvantages of DBS sampling, and to outline the steps involved in developing and validating an immunoassay for application to DBS samples. These steps include deciding on reagents, preparing calibration and quality control material, evaluating elution protocols, optimizing sample quantity, and assessing multiple aspects of assay performance, including intra- and interassay variation, lower limit of detection, accuracy, stability, and agreement between results from matched DBS and plasma samples. The broader goal of this "how-to" approach is to encourage investigators to validate, implement, and disseminate assay protocols for DBS samples in order to advance field-based research on human biology.

Targeted provision of oral iron: the evolution of a practical screening option

Universal oral iron supplementation, undertaken according to 1998 WHO guidelines, produced adverse consequences among some children in malaria-endemic areas. Prompted by the Pemba trial, which revealed excessive hospitalizations and deaths, WHO advised that iron supplementation in such regions be accompanied by previous screening for iron deficiency. This agenda, however, poses issues of cost, benefit, acceptability, technical feasibility, and reliability of such screening. The cost of equipment and personnel is balanced against savings from iron supplements spared and treatment for morbidity averted. Costs aside, the most efficacious acceptable screening approach for avoiding hospitalization and deaths must be fielded. Screening before supplementation can be used to assess hematological, iron, and possible inflammatory status to differentiate the source of decreased hemoglobin concentration. Iron deficiency has often been inferred from hematological status markers. The need for extraction of blood, albeit capillary in origin, and high assay costs limit the use of validated methods in screening. Noninvasive methods, i.e., not requiring the extraction of blood, provide the most acceptable and potentially least expensive approach for determining hematological or iron status. Although a noninvasive technique for iron and inflammatory status would be the ideal, it is unattained. Field-friendly, skin-probe hemoglobin devices, derived from instruments for clinical settings, are being developed and tested for eventual rollout in malarial areas. Given a firm grounding for the theoretical requirements needed to advance the screening agenda, evaluation and monitoring of the performance of screening devices can proceed hand in hand.

Choosing the types of biological sample to collect in longitudinal birth cohort studies

There are a variety of biological samples that can be collected from participants in longitudinal studies. Here we outline those that are particularly useful in longitudinal birth cohort studies starting in pregnancy, and discuss their advantages and disadvantages.

What a drop can do: dried blood spots as a minimally invasive method for integrating biomarkers into population-based research

Logistical constraints associated with the collection and analysis of biological samples in community-based settings have been a significant impediment to integrative, multilevel bio-demographic and biobehavioral research. However recent methodological developments have overcome many of these constraints and have also expanded the options for incorporating biomarkers into population-based health research in international as well as domestic contexts. In particular using dried blood spot (DBS) samples-drops of whole blood collected on filter paper from a simple finger prick-provides a minimally invasive method for collecting blood samples in nonclinical settings. After a brief discussion of biomarkers more generally, we review procedures for collecting, handling, and analyzing DBS samples. Advantages of using DBS samples-compared with venipuncture include the relative ease and low cost of sample collection, transport, and storage. Disadvantages include requirements for assay development and validation as well as the relatively small volumes of sample. We present the results of a comprehensive literature review of published protocols for analysis of DBS samples, and we provide more detailed analysis of protocols for 45 analytes likely to be of particular relevance to population-level health research. Our objective is to provide investigators with the information they need to make informed decisions regarding the appropriateness of blood spot methods for their research interests.

Use of the retinol-binding protein : transthyretin ratio for assessment of vitamin A status during the acute-phase response

The ratio plasma retinol-binding protein (RBP) : transthyretin (TTR) has been proposed as a means to improve the assessment of vitamin A status of individuals with concurrent infection or inflammation. We have measured RBP and TTR in stored sera from South African children who had accidentally ingested kerosene. Samples were collected from these children in hospital when suffering acute inflammation and respiratory distress, and from them and neighbourhood control children 3 months later. Vitamin A status was defined by modified relative dose response (MRDR) tests of liver retinol stores at 3 months and by serum retinol concentration both when children were ill and when they were well. Illness was defined as either being in hospital or, at follow-up, as having a raised plasma α1-acid glycoprotein (AGP) level. The RBP : TTR value was significantly decreased by both illness and low liver retinol stores. When the effects on RBP : TTR of illness and vitamin A stores were considered together for the 3-month follow-up samples, only vitamin A status significantly decreased the value. We calculated sensitivity and specificity of the RBP : TTR ratio against established measures of vitamin A status using a cut-off value of 0·3 for RBP : TTR and standard cut-off values for MRDR (0·06) and plasma retinol (0·7 μmol/l). Compared with MRDR, RBP : TTR had sensitivities of 76 % and 43 % and specificities of 22 % and 81 % to detect vitamin A deficiency in hospitalized and well children respectively. Compared with plasma retinol, sensitivities were 88 % and 44 % and specificities were 55 % and 64 % in hospitalized and well children respectively. Only for the case of clinically well children with biochemical evidence of subclinical inflammation did sensitivity (62 % and 100 % against MRDR and plasma retinol respectively) and specificity (100 % and 60 % against MRDR and retinol) approach useful levels for an assessment tool. Overall, although a trend supporting the theory behind the use of the RBP : TTR for assessment of vitamin A status in infection was observed in the current study, the ratio did not provide adequate sensitivity and specificity to be a useful assessment tool.

Ferritin concentrations in dried serum spots prepared by standard compared with simplified approaches: a validation study in Guatemala City

BACKGROUND

Spot ferritin assay on dried serum spot (DSS) samples provides reliable and accurate assessment. Standard DSS preparations, however, involve precise serum aliquots and require some skill and training of field personnel.

OBJECTIVE

We evaluated the validity of the spot ferritin assay on DSS samples prepared by simplified approaches and standard technique in Guatemala City.

DESIGN

Venous blood (5 mL) was obtained from 104 subjects aged 24 +/- 15 y (x +/- SD) and transferred into nonheparin-containing (2 plain and 2 self-sealing) capillary blood collection tubes. Three DSS samples were prepared: A (standard, 20 microL serum), B (blot, approximately 30-35 mm serum column), and C (dispenser, 20 microL serum pushed directly from self-sealing capillary tubes with a dispenser). Spots were air-dried and placed in hermetic plastic bags with a desiccant. Two weeks later, entire spots for DSS A and C samples and a circle in the center for DSS B samples were analyzed.

RESULTS

DSS ferritin A, B, and C correlated strongly with traditional ferritin (r = 0.71-0.88, P < 0.001). The geometric mean (-1 SD and +1 SD) values for the DSS A, B, and C and traditional ferritin methods were 27.5 (12.6, 60.2), 32.4 (13.5, 77.6), 27.5 (11.7, 64.6), and 30.2 (13.8, 66.1) microg/L, respectively, and did not differ significantly. The difference in ferritin values by various DSS approaches compared with the traditional approach was small (<4 microg/L; P > 0.05).

CONCLUSIONS

Simplified and standard DSS methods provide accurate iron-status assessment in population studies. The simplified DSS approaches for serum ferritin measurement need to be evaluated further in populations in whom iron deficiency is prevalent.

Multiple micronutrient deficiencies: future research needs

There has been a rising current of calls for a moratorium on international nutritional research in favor of an investment in intervention programs, per se. The topic of multiple-micronutrient supplementation reviewed at the International Workshop on Multi-Micronutrient Deficiency Control in the Life Cycle (May 30-June 1, 2001) has confirmed once again, however, the intimate interaction between program development and a supporting agenda of applied research. The areas of research required to produce successful intervention programs include biologic availability, safety and efficacy, communications and behavior, effectiveness, cost-effectiveness (efficiency), and food and pharmaceutical technology. Attention to safety and surveillance for unintended adverse effects has acquired new relevance as we analyze the multi-center International Research on Infant Supplementation (IRIS) I studies. All professionals involved in research projects in this area must assure both the quality and reliability of investigations and adhere to the highest principles of ethical conduct of research in human studies. The fundamental principles of research design and hypothesis development, quality assurance, reliability of measurements, and sound and unbiased interpretation of findings apply to all experimental science, and must be guaranteed for this mission. Agencies, academic institutions, and industry alike must work to create a system in which researchers can uphold these standards, and realize at the same time that the area of multi-micronutrient supplementation in developing countries can be a fertile area for training future researchers.

Ferritin concentrations in dried serum spots from capillary and venous blood in children in Sri Lanka: a validation study

BACKGROUND

Assessing iron status continues to be challenging in field situations. Spot methods developed for analyzing ferritin from serum or plasma samples that are spotted and dried on filter paper have been shown to provide reliable and accurate iron-status assessments. However, the spot methods are based on samples from venous serum or plasma and have not been evaluated in field settings.

OBJECTIVE

We evaluated the validity of analyzing ferritin to assess iron status by using venous and capillary dried-serum-spot (DSS) samples by the spot method compared with using serum ferritin by the traditional method in a field setting.

DESIGN

Venous and capillary blood was obtained from healthy schoolchildren (n = 100; +/- SD age: 8.9 +/- 0.3 y) in Colombo, Sri Lanka. To prepare DSS samples, we aliquoted precisely 20 microL serum per spot on filter paper, air-dried the spots, and placed them in airtight plastic bags until analysis by the spot ferritin method with the use of cellulase from Trichoderma reesei at 2 wk after collection. Venous serum (100 microL) was frozen until ferritin determination by traditional radioimmunoassay.

RESULTS

Venous and capillary DSS ferritin values correlated strongly with traditional serum ferritin values (r = 0.88 and 0.86, respectively; P = 0.0001). The geometric means (+/- 1 SD) for venous and capillary DSS ferritin and traditional ferritin were 26.9 (15.3-47.4), 33.9 (20.9-54.8), and 33.1 (18.6-58.8) microg/L, respectively, and were not significantly different. Venous and capillary DSS methods on average (+/- SD) yielded ferritin values that were 5.8 +/- 10.1 microg/L lower and 0.1 +/- 9.4 microg/L higher, respectively, than serum ferritin values obtained with the traditional method.

CONCLUSIONS

Capillary and venous DSS methods for analyzing ferritin provide accurate tools for assessing iron status. Furthermore, capillary DSS ferritin is a practical means of detecting iron deficiency in field settings.

Effectiveness and strategies of iron supplementation during pregnancy

Iron deficiency continues to be one of the most prevalent single-nutrient deficiencies in the world. Interventions are often designed to prevent the decrease in hemoglobin concentration and the decline in iron stores associated with pregnancy. Although this is believed to be desirable for both the health of the mother and the well-being of the growing fetus, some scientists disagree. Enrichment and fortification of food items, and dietary changes resulting from education interventions, have met with some success in developed countries, but not often in the developing world. A therapeutic approach to iron supplementation, rather than a public health-based approach, is used throughout much of the world but suffers from real, or perceived, problems of compliance. Large doses of iron are most often prescribed and are associated with side effects and with increased oxidative damage. Alternatively, delayed-release preparations and intermittent oral iron supplementation lead to better overall compliance and alleviate side effects. Daily iron intervention provides more protection against a decline in the storage iron pool in pregnant women than does an intermittent schedule, but the latter is generally associated with fewer side effects, better compliance, and possibly a reduction in risk of oxidative damage. An improved cost-benefit ratio associated with a lower-dose oral iron supplement may prove to be quite positive in the future. Currently, no single approach may be universally acceptable, although a moderate iron dosage protocol will likely provide the most benefit to those who require supplemental iron.

Dried Plasma Spot Measurements of Ferritin and Transferrin Receptor for Assessing Iron Status

Background: Efforts to reduce the high global prevalence of nutritional anemia require the use of both reliable laboratory assays to distinguish iron deficiency from other causes of anemia and cost-effective methods for collection of blood specimens under field conditions. The suitability of using small plasma samples spotted and dried on filter paper for measurements of plasma ferritin and transferrin receptor was evaluated in the present study.

Methods: Blood specimens obtained from 73 male and 83 female subjects (19–40 years) representing a wide range of iron status were used to perform parallel measurements of plasma ferritin and transferrin receptor on whole plasma and spotted plasma samples.

Results: Ratio plots, evaluating the acceptability and precision of the spot method in ferritin and transferrin receptor assays, showed the expected proportion of data points within the 95% prediction interval. In the composite group of 156 subjects, both the whole plasma and plasma spot methods gave a geometric mean transferrin receptor/ferritin ratio of 18. The regression equation for the ratio was logy = 1.045 logx − 0.05126; r = 0.986; P &lt;0.0001. The ratio of transferrin receptor/ferritin determined from plasma spots correctly identified all 12 subjects with iron deficiency anemia compared with 11 of the 12 for whole plasma measurements.

Conclusions: Measurements of ferritin and transferrin receptor on plasma spotted and dried on filter paper are comparable to whole plasma values for the identification of iron deficiency anemia. The use of dried plasma spots will facilitate the collection, storage, and transport of samples in epidemiological studies of anemia prevalence.

An Assessment of Dried Blood-Spot Technology for Identifying Iron Deficiency

The present study was undertaken to assess the feasibility of using ferritin and transferrin receptor measurements on dried capillary blood spots to identify iron deficiency (ID) in public health surveys. Measurements on serum and blood spots prepared from venous blood were performed in 71 healthy subjects, 41 of whom were iron-replete and 30 who had ID, either without (n = 20) or with (n = 10) anemia. Parallel measurements were performed on hemolyzed whole blood and washed hemolyzed red blood cells to assess the erythrocyte contribution of ferritin and transferrin receptor to dried blood samples. The concentration of ferritin in dried blood samples was threefold higher than serum assays due to the release of ferritin from hemolyzed erythrocytes, which diminished the usefulness of ferritin measurements for detecting ID. On the other hand, there was negligible erythrocyte contribution to the measurement of transferrin receptor in dried blood spots. The most sensitive parameter in dried blood spots was the ratio of receptor/ferritin, which was suitable for identifying iron-deficiency anemia (IDA), but less reliable than serum assays for detecting milder ID without anemia. We conclude that tandem measurements of serum ferritin and transferrin receptor in dried blood spots can be used to facilitate the identification of IDA in epidemiologic studies.

© 1998 by The American Society of Hematology.

An Assessment of Dried Blood-Spot Technology for Identifying Iron Deficiency

The present study was undertaken to assess the feasibility of using ferritin and transferrin receptor measurements on dried capillary blood spots to identify iron deficiency (ID) in public health surveys. Measurements on serum and blood spots prepared from venous blood were performed in 71 healthy subjects, 41 of whom were iron-replete and 30 who had ID, either without (n = 20) or with (n = 10) anemia. Parallel measurements were performed on hemolyzed whole blood and washed hemolyzed red blood cells to assess the erythrocyte contribution of ferritin and transferrin receptor to dried blood samples. The concentration of ferritin in dried blood samples was threefold higher than serum assays due to the release of ferritin from hemolyzed erythrocytes, which diminished the usefulness of ferritin measurements for detecting ID. On the other hand, there was negligible erythrocyte contribution to the measurement of transferrin receptor in dried blood spots. The most sensitive parameter in dried blood spots was the ratio of receptor/ferritin, which was suitable for identifying iron-deficiency anemia (IDA), but less reliable than serum assays for detecting milder ID without anemia. We conclude that tandem measurements of serum ferritin and transferrin receptor in dried blood spots can be used to facilitate the identification of IDA in epidemiologic studies.

© 1998 by The American Society of Hematology.