DBS: New Frontiers for an Established Technique
By: Gene Ray, Ph.D.
Dried blood spot (DBS) analysis is an established technique, expanding in usage for both clinical and pre-clinical bioanalytical investigations. DBS has been used since the 1970's to test newborns for a rare generic disorder known as phenylketonuria (PKU) which can lead to progressive brain damage if not caught early. The current approach utilizes a small amount of blood obtained from a heel stick. The blood is then placed on a card to test phenylalanine levels. Owing to its wide international acceptance, DBS has recently expanded for pharmacokinetic testing.
DBS offers several distinct advantages over conventional blood collection, due in part to the limited amount of blood required (25-40 mcL per spot).
- Toxicology. The limited sample volume needed reduces the number of animals required for pharmacokinetic (PK) studies. This not only cuts animal costs, but inherently improves PK profiles with multiple samplings per animal.
- Pediatrics. An obvious choice, since this is where DBS found its nascent application. The technique offers an additional advantage, reducing anxiety in young children by using a lance instead of venous blood drawn with a needle for sample collection.
- Global Trials. Since centrifuges, freezers, and electricity are not needed for sample processing, DBS is an ideal technique for international studies in outlying areas and underdeveloped nations. Further, it eliminates high shipping costs and the need for large quantities of dry ice as would be required for conventional samples.
- Therapeutic Drug Monitoring. As with the widely known practice of blood sugar monitoring in patients with diabetes, DBS has the potential for routine applications of monitoring therapeutic levels of drugs in the blood stream. Patients can simply place the card into an envelope and mail it directly from home rather than visit a lab or their doctor's office.
KCAS has used DBS for pre-clinical PK evaluations and is involved in an NIH grant in cooperation with Children’s Mercy Hospital in Kansas City, MO for a pediatric patient study.
As with any technique, there are limitations in DBS because of the small amount of blood used and from the physical process in drying.
- Assay Sensitivity. Studies which require low limits of quantitation may not be suitable for DBS. In general, concentrations requirements below 1 ng/mL may be better suited using conventional plasma or whole blood collection.
- Unstable Compounds. Drugs which are inherently unstable may degrade during drying process. Although the spots can be deriviatized upon collection onto the card, this approach has its limitations.
- Large Molecule Compounds. DBS has been used for both enzyme and protein assays, but the physical process of drying may damage and limit the extraction of the molecule from the dried matrix.
- Variation in Hematocrit. Patient or animal blood with either low or high hematocrit levels can cause inconsistent spotting on cards. New DBS cards have been introduced using a fiberglass format that may overcome this issue.
- Regulatory Acceptance. Although DBS has been used for PKU screening for over 40 years, the FDA has not officially weighed in on its use for new applications.
The distinct advantages of DBS analysis continue to establish this method as a suitable alternative to traditional collection and sampling/testing practices. KCAS anticipates that in 2013 the FDA will finalize their opinion on the use of DBS in new applications. DBS is also being evaluated for both urine and cerebral spinal fluid (CSF) studies. Since several drugs are reported to bind tenaciously to plastics from urine and CSF collections, this technique may well eliminate the problem.
You can learn more about DBS analysis by viewing our poster, here. For more information about DBS or any projects you are working on, please contact us.