Introduced by Robert Guthrie in the 1960s, dried blood spot (DBS) sampling involves taking small drops of blood from either a finger prick (or heel prick in neonates) and depositing them on specially manufactured absorbent card where they are allowed to dry. Once dry, DBS cards can be readily transported by post for analysis since the components of the blood remain unchanged for several days, even at room temperature. For analysis, a portion of the blood spot is removed from the card and placed in a solvent to extract the analyte(s) of interest. Therein lies the elegance and ease of the DBS sampling system: no specialist collection, no liquid blood, and no refrigerants. Guthrie card samples have seen widespread and routine use for neonatal screening of metabolic disorders, such as phenylketonuria, sickle cell disorders, and HIV infection.
Introduced by Robert Guthrie in the 1960s, dried blood spot (DBS) sampling involves taking small drops of blood from either a finger prick (or heel prick in neonates) and depositing them on specially manufactured absorbent card where they are allowed to dry. Once dry, DBS cards can be readily transported by post for analysis since the components of the blood remain unchanged for several days, even at room temperature. For analysis, a portion of the blood spot is removed from the card and placed in a solvent to extract the analyte(s) of interest. Therein lies the elegance and ease of the DBS sampling system: no specialist collection, no liquid blood, and no refrigerants. Guthrie card samples have seen widespread and routine use for neonatal screening of metabolic disorders, such as phenylketonuria, sickle cell disorders, and HIV infection. To be a truly useful sampling system, DBS must be used in conjunction with analytical techniques capable of detecting the low levels of analytes present in just a few micrograms of dried blood. Indeed, the combination of DBS with state-of-the-art instrumentation such as liquid chromatography–tandem mass spectrometry (LC-MS/MS) has led to widespread use of the technique in clinical and drug discovery applications. Whilst this combination has become synonymous with DBS bio analysis, there are many other analytical techniques that can be used to obtain valuable information from a DBS sample, as shown in Table 1.
Notes: NBS =newborn screening, TDM = therapeutic drug monitoring and DMPK = drug metabolism/pharmacokinetics
Certainly along with improvements to analytical sensitivity comes the drive to fully quantify components extracted from dried blood spots. Under these circumstances the extraction process assumes a major importance. Punching a fixed diameter disc from the spot provides a level of quantification but at a cost – the time and effort needed to deal with the punched disc (see Figure 2) and the possible loss in sensitivity as a result of not using the whole sample. Automation of the punching process and disc handling can help but the process is still complex. An alternative is to simply extract a fixed volume of the spot by passing a solvent through the spot whilst it is still on the card, which can be achieved by clamping two tubes opposite each other, on either side of the spot, and passing a fixed volume of solvent through that part of the spot. Provided there is no significant loss of solvent into the card, automatic extraction/quantification becomes possible. The advent of sophisticated instrumentation capable of quantifying the levels of analytes in DBS samples has led to the recent surge in interest in this sample collection technique.
Please read the other articles in this series:
Spot On
Principal Drivers for DBS Research
Confronting Concerns
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