Dried blood spot (DBS) testing offers a simplified and less invasive approach to collecting blood samples. This method involves collecting a small amount of blood, typically from a finger or heel, onto a specialized filter paper. The blood then dries on the paper, creating a stable sample that can be easily transported and analyzed. DBS testing has gained recognition for its utility in various medical and research settings.
The Basics of Dried Blood Spot Testing
A dried blood spot is created when a small volume of blood is applied to an absorbent filter paper. Once the blood is absorbed, it undergoes a drying process, which stabilizes the blood components. This stabilization helps preserve the analytes—the substances being measured—within the blood, making them suitable for later analysis.
The scientific principle behind DBS relies on the ability of the filter paper matrix to bind and preserve biological material, such as DNA, RNA, and proteins, by removing water, which can otherwise lead to degradation. After drying, a small disc, or “punch,” is taken from the saturated area of the filter paper for laboratory analysis.
The Collection Process
Collecting a DBS sample is a straightforward procedure. For adults and older children, a finger prick is the common collection site. For infants, a heel prick is often used.
Before collection, the chosen site is cleaned with an alcohol swab and allowed to air dry completely. A sterile lancet is used to create a small puncture, and the first drop of blood is wiped away to ensure a clean sample.
Large drops of blood are then gently touched to the pre-printed circles on the filter paper, ensuring the blood completely saturates the paper. Avoid touching the filter paper directly to the skin or layering multiple drops of blood on the same spot. Once all circles are filled, the card is left open to air dry at room temperature for several hours. After complete drying, the card is placed in a sealed bag with a desiccant packet to protect against humidity during storage and transport to the laboratory.
Key Advantages of Dried Blood Spot Testing
DBS testing offers several benefits over traditional blood collection methods like venipuncture. One advantage is its minimally invasive nature, requiring only a small finger or heel prick. This makes it less painful and stressful, especially for children and those with difficulty accessing veins. This ease of collection allows samples to be taken at home or in remote locations, improving access to diagnostic testing.
The reduced sample volume needed for DBS testing is another benefit, as only a few drops of blood are required. Once dried, DBS samples are stable at room temperature, eliminating the need for refrigeration or specialized coolants during storage and transport. This stability simplifies logistics, reduces shipping costs, and makes DBS an effective method for large-scale population studies and health programs in areas with limited infrastructure. The drying process can also inactivate many pathogens, lowering the biohazard risk for those handling the samples.
Key Applications Across Healthcare and Research
DBS testing is widely used across various medical and research domains. A primary application is newborn screening for inherited metabolic disorders, such as phenylketonuria (PKU) and congenital hypothyroidism. This early detection allows for timely interventions that can prevent serious complications and improve long-term health outcomes for infants. DBS is also used to screen for conditions like cystic fibrosis and sickle cell disease in newborns.
The method is also used in monitoring infectious diseases. DBS samples are suitable for testing antibodies, antigens, or nucleic acids related to infections like HIV and hepatitis B and C. This is useful in hard-to-reach populations or in resource-limited settings, where traditional blood draws and cold chain transport may be challenging. For instance, DBS can detect the genetic material of the HIV virus in infants, preventing false positives that might occur from maternal antibodies.
Beyond screening, DBS supports therapeutic drug monitoring, where drug levels in a patient’s blood are measured to ensure effective and safe dosing. It is also used in clinical research and population studies for long-term health monitoring and biomarker analysis. In preclinical drug development and toxicology studies, DBS provides a convenient way to collect samples for pharmacokinetic studies, which track how drugs move through the body.
Considerations for Reliable Analysis
While DBS offers benefits, certain factors influence the quality and reliability of results. Achieving proper sample volume is important; the blood spot should completely fill the designated circle on the filter paper. Inconsistent blood spot size or uneven saturation can affect the accuracy of measurements.
The hematocrit, which is the proportion of red blood cells in the blood, can impact how analytes distribute within the dried blood spot and how they are absorbed by the filter paper. Variations in hematocrit can lead to differences in the concentration of the substance being measured. Laboratories address this by using standardized protocols for sample preparation and analysis, sometimes involving calibration strategies or adjusting for hematocrit levels.
Standardized collection and drying procedures are important to ensure consistent sample quality and minimize variability. Analytical methods, such as liquid chromatography coupled with mass spectrometry (LC-MS/MS), are used to measure analytes from DBS samples due to their sensitivity and specificity. Despite these considerations, DBS remains a reliable method when established protocols are carefully followed.