The Case for Fresh Blood: Why Field-Prepared Smears Beat the Lab Wait

Oct 5, 2026

For many conditions, particularly those diagnosed by examining the morphology (shape and structure) of blood cells, a peripheral blood smear (PBS) is a vital diagnostic tool. Yet, the journey a blood sample takes from a patient to a central laboratory can compromise the integrity of specimen leading to an inadequate sample or diagnostic errors. When it comes to blood smears, fresh is always best, and field preparation often leads to a more accurate, reliable diagnosis than smears made from transported blood.

The Problem of Blood Degradation During Transport

Once blood is drawn and placed into an anticoagulant, such as EDTA, a countdown begins. Cellular changes, known as storage artifacts, can start to occur rapidly, especially if the sample is not kept under optimal conditions. Handling and transport of the specimen can also result in hemolysis of the specimen.

Delays in processing can lead to significant morphological alterations in red blood cells (RBCs) and white blood cells (WBCs), which can be mistaken for actual disease features, leading to a misdiagnosis (Shaista Choudhary et al., 2020; Act Scientific, 2021).

Features Lost or Altered in Degraded Samples

When a blood specimen degrades during transport, critical diagnostic features can be obscured or misleading artifacts can be created. This can severely limit the hematologist's ability to interpret the smear accurately.

• Red Blood Cell (RBC) Changes:

• Crenation (Echinocytes): Normal RBCs can develop spiky, abnormal projections (crenations) after just a few hours of storage at room or refrigerator temperatures, sometimes mistaken for signs of conditions like uremia (Act Scientific, 2021; eClinpath, 2013).

• Spherocytes: Changes like the formation of spherocytes, round cells without a central pale area, can be observed with increased storage time, potentially confounding the diagnosis of conditions like hereditary spherocytosis (Act Scientific, 2021; ResearchGate, 2020).

• Parasite Morphology: For infectious diseases like Malaria, the delicate structure of the parasite within the RBCs can be distorted, making accurate species identification difficult or impossible (CDC, 2018).

• White Blood Cell (WBC) Changes:

• Nuclear Changes: WBC nuclei can show signs of degeneration, such as pyknosis (nuclear condensation), vacuolization of the cytoplasm, or changes that mimic true pathological conditions like the Pseudo-Pelger-Huët anomaly (Shaista Choudhary et al., 2020; Act Scientific, 2021).

• False Left Shift: Neutrophil nuclei can swell and appear less condensed, potentially leading to a misinterpretation of a "false band" or "false left shift," preventing an accurate differential count (eClinpath, 2013).

The Value of Fresh Blood Smears

Ideally, blood smears should be prepared immediately after collection, especially if anticoagulated blood is used, or preferably, directly from a finger or heel prick (fresh blood without anticoagulant).

Smears prepared in the field with fresh blood allow for the visualization of blood cells in their closest-to-in-vivo state, preserving the subtle morphological features essential for diagnosis (Act Scientific, 2021; CDC, 2018). While refrigerated transport can minimize the effects of deterioration on some parameters, for the peripheral blood smear's structural and morphological analysis, the fastest way to stabilize the cells is by drying and fixing them onto a slide before degradation sets in.

Performing a PBS examination immediately is recommended to obtain the most significant and accurate results, particularly when evaluating cell morphology (ResearchGate, 2020). By prioritizing the immediate preparation of a blood smear, clinicians can reduce the risk of artifacts, ensuring the integrity of the sample for diagnosis.

The Issue with Field Smears

Blood smear preparation is a delicate and skill oriented task. It is best accomplished in a controlled setting such as a laboratory. Field veterinarians have cited the lack of a leveled surface, such as a table, as a key limiting factor in their ability to prepare adequate blood smears.

The RapidSmear is a portable device that fits into any medical supply bag. It has a built in base that houses the specimen glass slide while keeping everything leveled during use. The RapidSmear’s wiper also eliminates common human errors such as the pitch and angle of the smearing edge during the smear process.

Learn more about the RapidSmear here.