1 History and development

Dried blood spot sampling emerged as a practical alternative to conventional liquid blood collection. Its appeal lies in the combination of simplicity, low cost, and the ability to preserve small samples for later analysis. Over time, the method moved from a niche laboratory technique to a widely adopted tool in screening programs and clinical research.

1.1 Early use in laboratory medicine

Early laboratory applications focused on the convenience of collecting a small amount of blood on absorbent paper for delayed testing. Researchers recognized that drying the specimen could reduce the need for immediate processing while still preserving many measurable analytes. This made the method useful in settings where centrifugation, refrigeration, or rapid transport were difficult.

1.2 Newborn screening adoption

The technique became especially important in newborn screening, where only a tiny blood sample is needed for testing multiple inherited conditions. The dried format allowed hospitals and public health programs to collect samples soon after birth and send them to central laboratories. This helped establish dried blood spot cards as a standard specimen type in population-based screening.

1.3 Expansion into modern diagnostics

With advances in analytical chemistry and molecular biology, dried blood spots began to support a broader range of tests. Laboratories developed methods for measuring drugs, hormones, proteins, metabolites, and nucleic acids from dried samples. As a result, the technique expanded beyond screening into monitoring, epidemiology, and field-based diagnostics.

2 Collection procedure

Dried blood spot collection is designed to be straightforward, but consistent technique is important for reliable results. The blood is applied directly to an absorbent surface, where it spreads by capillary action and dries before further handling. Proper collection reduces variability and improves test accuracy.

2.1 Sample collection devices

Collection commonly uses specially manufactured filter paper cards with preprinted circles or marked areas. Some systems include lancets, protective packaging, drying racks, and desiccant materials. The absorbent card is selected to support uniform spreading and compatibility with downstream testing.

2.2 Finger prick and heel prick methods

For older children and adults, a finger prick is often used to obtain capillary blood. In newborns, a heel prick is more common because it is practical and suitable for small volumes. In both methods, the blood must flow freely enough to form drops without excessive squeezing, which can affect sample quality.

2.3 Spotting and drying process

Drops of blood are placed onto the card so that each spot fills the printed circle as evenly as possible. The card is then left to dry in a clean, horizontal position away from heat, direct sunlight, and contamination. Drying time varies by environment, but complete drying is essential before packaging or transport.

2.4 Labeling and handling requirements

Each card should be labeled clearly with identifying information, collection date, and relevant clinical details. Handling instructions typically emphasize avoiding contact between spots, preventing stacking while wet, and keeping the sample free from moisture. Careful labeling and documentation support traceability and accurate interpretation.

3 Specimen types and materials

Dried blood spot testing can use blood from different collection routes and on different paper substrates. The choice depends on the intended assay, the available collection setting, and the expected sample volume. Material properties can influence absorption, uniformity, and analytical performance.

3.1 Filter paper cards

Filter paper cards are the standard material for dried blood spot collection. They are engineered to absorb blood consistently and to support reproducible punch sampling in the laboratory. Some cards are treated or calibrated for specific testing workflows, while others are general-purpose.

3.2 Capillary blood samples

Capillary blood obtained from a fingertip or heel is the most common source for dried blood spots. It is convenient for point-of-care and decentralized collection because it requires only a small puncture. However, capillary blood may differ slightly from venous blood in composition, which can matter for some assays.

3.3 Venous blood applications

Venous blood can also be applied to filter paper when larger collection programs or specific assays require it. This approach may improve sample control in certain laboratory protocols, especially in research settings. Even so, attention to volume, spotting technique, and drying remains necessary.

4 Laboratory processing

Once received in the laboratory, dried blood spot specimens undergo a series of preparation steps before analysis. These steps are intended to isolate a defined portion of the sample and transfer analytes into a liquid medium or directly into the instrument workflow. Standardization is important because the matrix is physically different from whole blood in a tube.

4.1 Punching and extraction

A mechanical punch is often used to remove a circular disk from the dried spot. The punch size and location can influence how much blood is represented in the test portion. The punched disk is then extracted with solvent or buffer so that the target analytes can be measured.

4.2 Elution methods

Elution refers to the process of releasing analytes from the dried matrix into solution. Conditions such as incubation time, temperature, solvent composition, and agitation can affect recovery. Optimized elution procedures are selected according to the compound being measured and the platform used for detection.

4.3 Analysis platforms

Different analytical platforms can be applied to dried blood spot extracts, depending on the clinical question. Some tests are designed for routine high-throughput screening, while others require highly sensitive instrumentation. The dried format can be compatible with both targeted assays and broader profiling methods.

4.3.1 Immunoassays

Immunoassays detect specific proteins, hormones, or infectious markers using antibody-based recognition. They are often used when rapid processing and moderate sensitivity are sufficient. In dried blood spot workflows, assay performance depends on extraction efficiency and matrix effects.

4.3.2 Molecular testing

Molecular testing detects DNA or RNA targets from dried blood spots. This is useful for genetic screening, pathogen detection, and retrospective studies when stored samples are available. The dried format can preserve nucleic acids well enough for amplification-based methods under appropriate conditions.

4.3.3 Mass spectrometry

Mass spectrometry is widely used for small molecules, metabolites, and therapeutic agents. It allows precise quantification and can support multiplex testing from a single punch. Because of its sensitivity, it is especially valuable when only a limited amount of blood is available.

5 Clinical applications

Dried blood spot testing supports a broad range of medical uses. Its advantages make it suitable for screening, follow-up testing, and longitudinal monitoring. The method is especially helpful when transporting liquid blood would be difficult or expensive.

5.1 Newborn screening

Newborn screening remains one of the best-known applications. It enables early detection of certain inherited disorders before symptoms develop, allowing prompt treatment or follow-up. The ability to test many conditions from a single specimen has made dried blood spots central to these programs.

5.2 Infectious disease testing

The method is also used for detecting antibodies, antigens, or nucleic acids associated with infectious diseases. It can support surveillance, remote testing, and epidemiologic studies. Because samples are dry and compact, they are useful in settings where cold-chain transport is limited.

5.3 Metabolic disorder monitoring

Patients with metabolic disorders may undergo repeated dried blood spot testing to monitor disease markers or treatment response. The small sample requirement is convenient for long-term follow-up, especially in children. Serial testing can help clinicians assess whether therapy is maintaining target levels.

5.4 Therapeutic drug monitoring

Dried blood spots can be used to measure concentrations of medications in blood. This is helpful for drugs that require close dose adjustment or where adherence is an issue. The method may also facilitate home collection when regular clinic visits are impractical.

5.5 Hormone and biomarker analysis

Hormones, inflammatory markers, and other biomarkers can sometimes be measured from dried specimens. This has broadened the method’s use in endocrinology, population studies, and research trials. The approach is particularly useful when repeated small-volume sampling is preferred.

6 Advantages

Dried blood spot collection offers several practical benefits over conventional venous sampling. These advantages have driven its adoption in public health, research, and decentralized care. Many of its strengths relate to simplicity and portability.

6.1 Minimal invasiveness

The collection procedure requires only a small puncture, making it less invasive than venipuncture. This can improve acceptance in infants, children, and people who prefer simpler sampling methods. Reduced invasiveness also helps when repeated collections are needed.

6.2 Low sample volume requirements

Only a few drops of blood are needed for many assays. This is especially valuable in newborns or patients with limited accessible blood volume. A single card can sometimes support multiple tests, depending on how much material is available.

6.3 Simplified storage and transport

Dried samples are easier to store and ship than liquid blood. They often do not require immediate centrifugation and may be transported with less dependence on refrigeration. This makes the method cost-effective for centralized laboratories.

6.4 Suitability for remote settings

Because the technique is simple and portable, it works well in rural clinics, field studies, and mobile health programs. Samples can be collected far from the testing laboratory and still remain usable if handled correctly. This has expanded diagnostic access in under-resourced areas.

7 Limitations and challenges

Despite its usefulness, dried blood spot testing has technical constraints. Some arise from the physical properties of the blood sample, while others are related to collection variability and assay design. These factors can limit comparability with standard liquid blood methods.

7.1 Hematocrit effect

The hematocrit, or proportion of red blood cells, can change how blood spreads on the paper. Higher or lower hematocrit values may alter spot diameter and analyte distribution. This can introduce measurement bias if the assay does not account for the effect.

7.2 Spot size and volume variability

Not every spot contains the same volume of blood, even when the visible size appears similar. Differences in drop formation, card saturation, and drying behavior can affect the amount analyzed. This makes accurate volumetric interpretation more complex than with liquid aliquots.

7.3 Contamination and degradation

Samples may be affected by contamination from skin, environmental exposure, or improper handling. Heat, humidity, and prolonged storage can also degrade certain analytes. For this reason, collection and storage conditions must be carefully controlled.

7.4 Analytical standardization issues

Methods may differ across laboratories in card type, punch size, extraction procedure, and calibration strategy. These variations can reduce comparability between studies or institutions. Standardized protocols are therefore important for reproducible results.

8 Storage and transport

The stability of dried blood spots depends on how they are dried, packaged, and stored. Environmental conditions influence both short-term transport and long-term preservation. Good specimen management helps maintain analyte integrity.

8.1 Drying conditions

Specimens should dry fully before being sealed or stacked. Inadequate drying can promote microbial growth or analyte loss. A clean, dust-free environment is preferred to reduce contamination during this stage.

8.2 Temperature and humidity considerations

Cool, dry storage generally improves stability for many analytes. High humidity can accelerate degradation or cause spots to smear and absorb moisture. Temperature extremes may also affect certain proteins, enzymes, or nucleic acids.

8.3 Stability over time

Some analytes remain stable for long periods, while others decline more quickly. Stability depends on the target compound, the paper type, and the storage environment. Laboratories often validate acceptable storage durations for each assay.

8.4 Mailing and biobanking

Dried blood spots are frequently mailed to laboratories in protective envelopes. Their compact form makes transport simple and inexpensive. They are also suitable for biobanking, where archived cards may be used later for research or retrospective testing.

9 Quality control and standardization

Reliable dried blood spot testing depends on consistent collection and laboratory practice. Quality control begins at the point of sample collection and continues through analysis and reporting. Standardization supports accuracy across different users and sites.

9.1 Collection training

Personnel who collect samples must be trained to obtain adequate spots and avoid common errors. Proper training includes site preparation, correct drop placement, drying procedures, and documentation. Good technique reduces rejection rates and analytical variability.

9.2 Reference materials

Reference materials help laboratories calibrate methods and compare results over time. These materials may be prepared to mimic dried blood spot specimens as closely as possible. They are especially useful for validating extraction efficiency and instrument performance.

9.3 Validation of assays

Each assay intended for dried blood spot use should be validated for the specific matrix. Validation examines accuracy, precision, detection limits, recovery, and interference. Because dried samples behave differently from liquid blood, direct transfer of methods is not always appropriate.

9.4 Regulatory and laboratory guidelines

Laboratories often follow established guidelines for specimen acceptance, documentation, and result interpretation. Regulatory expectations may vary by country and by test type, but they generally emphasize traceability and verified performance. Clear protocols help ensure that results are clinically meaningful.

10 Safety and ethical considerations

Although dried blood spots are small and easy to handle, they still contain human biological material. Safe collection and responsible use are essential. Ethical issues are especially relevant when samples are stored for future analysis or used in screening programs.

10.1 Biosafety precautions

Collectors and laboratory staff should use standard precautions to avoid exposure to bloodborne pathogens. Gloves, proper disposal of lancets, and clean work surfaces reduce risk. Dried samples should still be treated as potentially infectious material until processed according to policy.

Individuals or guardians may need clear information about what the sample will be used for, especially if it may be stored beyond immediate testing. Privacy protections are important because dried cards can contain identifiable health information. Policies should address access, retention, and secondary use.

10.3 Use in population screening

When used for screening large groups, the method must balance public health benefits with individual rights and follow-up needs. Programs generally rely on clear procedures for notification, confirmatory testing, and referral when results are abnormal. Transparent governance helps maintain trust in screening systems.