The Measurement of Micronutrient Deficiencies - A Long Way to Go
Analysis of the micronutrient status of populations affected by natural and complex nutritional emergencies poses special problems. However, it is also widely regarded as being of great importance, by nutritionists at least, in surveillance and monitoring the effectiveness of interventions. But why specifically does it matter that we should be able to accurately determine the prevalence and severity of micronutrient deficiency diseases? Appropriate treatment of individual patients, resource allocation for population interventions, and advocacy for action from policy makers and donors are all much more easily achieved if reliable and believable data is available. Reliance on clinical signs may not be sensitive or specific for some deficiencies and will only tend to detect the advanced stages of deficiency. As an example, the difficulties in diagnosing Beriberi have been discussed in a previous edition of Field Exchange (Golden, 1997). For the measurement of micronutrient status in the field the following criteria would ideally be met:
- Sensitive and specific test
- Rapid and simple procedure involving a one-point determination
- Test can be performed with minimal training
- Method does not require the taking of venous blood samples
- Results can be made available in the field and at HQs in a form which facilitates decision making.
At present few tests are available which meet all these criteria and for many micronutrients no practical biochemical assessments are currently possible in the difficult circumstances encountered in the field. This is partly because the instability of vitamins and the interference provided by other substances in biological samples make analysis a complex and demanding task. Recent promising developments include a dipstick test for determining the level of iodine in urine, the use of a visual dark adaptometry test for diagnosing vitamin A deficiency. For anaemia screening in the field, recent work on the WHO Colour Scale indicates that it may present a much cheaper alternative to the widely used haemoglobin photometer. However, for many micronutrients there are currently no reliable field-friendly methodologies.
The need for improved filed
diagnostic and survey methods has led us, and others, to pursue the development
of tests which can be used to measure the level of micronutrients on blood
spots dried onto filter paper. Blood-spot technology offers a number of
particular advantages. The technology was developed by Guthrie in
1963 for the screening of phenylketonuria and has since been used for numerous
applications. Small samples are whole blood are taken from a finger or
heel prick using a sterile disposable lancet, stabilisation and preservation
of the sample is achieved by drying of the blood onto the filter paper
matrix and these can then be easily transported by postal services.
Significant advantages of this technique compared to venous sampling are
the reduction in the risk of exposure to infective blood and the ease and
low cost of sample collection. The stability of the micronutrient
within the matrix of the filter papers may often be good, especially when
stored out of sunlight and in the presence o desiccants, but requires confirmation
for each particular application. However, the first requirement for such
an application is that laboratory analysis of the micronutrients in the
dried blood can be performed sensitively and reliably. One of the current
projects we are engaged in is to develop a novel way of detecting a range
vitamins in dried blood spots. Of course, even if technological developments do contribute to improvements in the quantity and quality of information on the micronutrient status of vulnerable populations the task of ensuring an appropriate response in a world of relatively reducing resources will remain huge. Nevertheless, we think it is worth the pursuit.
Andrew Seal PhD. Researcher
in Public Health Nutrition.Centre for International Child Health,Institute
of Child Health, 30 Guilford
Street, London, WC1N 1EH
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Reference this page
The Measurement of Micronutrient Deficiencies - A Long Way to Go. Field Exchange 5, October 1998. p12. www.ennonline.net/fex/5/go