New system to measure dry blood samples used in infant HIV screening, testing for metabolic disorders

Researchers from The University of Texas at Arlington have demonstrated that electrical conductivity can be an effective means to precisely measure the amount of blood present in dry blood spot analysis, providing a new alternative to the current preferred approach of measuring sodium levels.
Dry blood spots are a pinprick of blood blotted on filter paper and allowed to air dry, which is then sent to a laboratory for analysis. Simple and inexpensive, dry blood spot analysis is routinely used to screen newborns for metabolic disorders and has also proven effective in diagnosing infant HIV infection, especially in developing countries where health budgets are limited.
‘Our new method, which involves using an electrode probe to measure electrical conductivity, has proven accurate to within one percent,’ said Purnendu Dasgupta, Hamish Small Chair in Ion Analysis and James Garrett Professor in UTA’s Department of Chemistry and Biochemistry. ‘It also has the considerable advantage of using up none of the sample where the currently preferred approach uses around half the sample.’

Dasgupta and his co-researchers used 12 volunteers aged 20 to 66, taking pinpricks of blood and letting the dry blood spot samples dry. They then took a 3 millimeter punch out of each dry blood spot, dissolved the punch in methanol and water mixtures and used a dip-type small diameter ring-disk electrode to measure the conductance of the samples, determining the minimum immersion depth that proved accurate in measuring the amount of blood to within one percent.
‘As analytical instrumentation has improved, dry blood spot analysis is becoming increasingly popular for clinical trials to monitor the effects of therapeutic drugs and for large-scale epidemiology and genetic studies, where it is vital to know the exact amount of blood in the sample,’ Dasgupta said. ‘Our new dip probe method offers clear advantages, but it does have the same problem as measuring sodium in that it does not function if the subject has abnormal electrolyte levels, which happens in some diseases.’