title: Dried blood spots as a source of anti-malarial antibodies for epidemiological studies.
abstract: BACKGROUND
  Blood spots collected onto filter paper are an established and convenient source of antibodies for serological diagnosis and epidemiological surveys. Although recommendations for the storage and analysis of small molecule analytes in blood spots exist, there are no published systematic studies of the stability of antibodies under different storage conditions.
  
  
  METHODS
  Blood spots, on filter paper or glass fibre mats and containing malaria-endemic plasma, were desiccated and stored at various temperatures for different times. Eluates of these spots were assayed for antibodies against two Plasmodium falciparum antigens, MSP-119 and MSP2, and calculated titres used to fit an exponential (first order kinetic) decay model. The first order rate constants (k) for each spot storage temperature were used to fit an Arrhenius equation, in order to estimate the thermal and temporal stability of antibodies in dried blood spots. The utility of blood spots for serological assays was confirmed by comparing antibodies eluted from blood spots with the equivalent plasma values in a series of samples from North Eastern Tanzania and by using blood spot-derived antibodies to estimate malaria transmission intensity in this site and for two localities in Uganda.
  
  
  RESULTS
  Antibodies in spots on filter paper and glass fibre paper had similar stabilities but blood was more easily absorbed onto filter papers than glass fibre, spots were more regular and spot size was more closely correlated with blood volume for filter paper spots. Desiccated spots could be stored at or below 4 degrees C for extended periods, but were stable for only very limited periods at ambient temperature. When desiccated, recoveries of antibodies that are predominantly of IgG1 or IgG3 subclasses were similar. Recoveries of antibodies from paired samples of serum and of blood spots from Tanzania which had been suitably stored showed similar recoveries of antibodies, but spots which had been stored for extended periods at ambient humidity and temperature showed severe loss of recoveries. Estimates of malaria transmission intensity obtained from serum and from blood spots were similar, and values obtained using blood spots agreed well with entomologically determined values.
  
  
  CONCLUSIONS
  This study has demonstrated the suitability of filter paper blood spots paper for collection of serum antibodies, and provided clear guidelines for the treatment and storage of filter papers which emphasize the importance of desiccation and minimisation of time spent at ambient temperatures. A recommended protocol for collecting, storing and assaying blood spots is provided.
authors.affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London WC1E 7HT, UK. patrick.corran@lshtm.ac.uk
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Corran
authors.forename: Jackie
authors.initials: J
authors.lastname: Cook
authors.forename: Caroline
authors.initials: C
authors.lastname: Lynch
authors.forename: Heleen
authors.initials: H
authors.lastname: Leendertse
authors.forename: Alphaxard
authors.initials: A
authors.lastname: Manjurano
authors.forename: Jamie
authors.initials: J
authors.lastname: Griffin
authors.forename: Jonathan
authors.initials: J
authors.lastname: Cox
authors.forename: Tarekegn
authors.initials: T
authors.lastname: Abeku
authors.forename: Teun
authors.initials: T
authors.lastname: Bousema
authors.forename: Azra C
authors.initials: AC
authors.lastname: Ghani
authors.forename: Chris
authors.initials: C
authors.lastname: Drakeley
authors.forename: Eleanor
authors.initials: E
authors.lastname: Riley
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood*; D000953:Antigens, Protozoan / Q000276:immunology; D001769:Blood / Q000276:immunology*; D003890:Desiccation; D005898:Glass; D006801:Humans; D006813:Humidity; D007074:Immunoglobulin G / Q000097:blood; D016778:Malaria, Falciparum / Q000175:diagnosis* / Q000276:immunology; D020066:Merozoite Surface Protein 1 / Q000276:immunology; D010209:Paper; D010963:Plasmodium falciparum / Q000276:immunology; D015800:Protozoan Proteins / Q000276:immunology; D012680:Sensitivity and Specificity; D016036:Seroepidemiologic Studies; D013048:Specimen Handling / Q000379:methods*; D013636:Tanzania; D013696:Temperature; D013997:Time Factors; D014454:Uganda
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D007074:Immunoglobulin G; D020066:Merozoite Surface Protein 1; D015800:Protozoan Proteins; C009753:fiberglass; C065974:merozoite surface protein 2, Plasmodium