Abstract
BackgroundBlood 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.MethodsBlood 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.ResultsAntibodies 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°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.ConclusionThis 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.
Highlights
Blood spots collected onto filter paper are an established and convenient source of antibodies for serological diagnosis and epidemiological surveys
This paper presents the results of these studies together with a validated protocol for collection, storage and use of blood spots for antibody quantitation
To determine the efficiency of antibody recovery from blood spots collected in the field, paired blood spots and serum samples were collected by finger prick from individuals attending the dispensary at Msitu wa Tembo, Lower Moshi in Northern Tanzania [34]
Summary
Blood spots collected onto filter paper are an established and convenient source of antibodies for serological diagnosis and epidemiological surveys. When carrying out serological surveys, in remote locations, it is of great advantage to have a method of collecting and storing blood samples which does not require that facilities for centrifugation are accessible, and which is relatively robust to irregular degrees of refrigeration, at least for short periods. More recently blood spots have been used as a source of DNA for screening for genetic abnormalities in newborns, for example for cystic fibrosis and haemoglobinopathies [2,3]. Dried blood spots have been useful for isolating parasite DNA in mapping the spread of drug resistance in malaria parasites [23,24]
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