When detergent-based cleaning cycles fail to soften cellular debris or other materials causing a clog in the Sample Injection Tube (SIT), mechanical methods must be employed. While using a metal stylus to push and break apart stubborn clogs is a common approach, it may inadvertently force debris toward the flow cell. Therefore, using a syringe to try and pull out the clog is generally preferred. Alternatively, a more invasive method involves removing the SIT and using ultrasonic cleaning (sonication) to break apart the clog.

Procedure monitoring is essential in laboratory operations to ensure compliance with Standard Operating Procedures (SOPs), maintaining consistency, safety, and quality. It enables early detection of deviations or errors, supports quality control through proper documentation, and enhances reproducibility by ensuring uniform execution across users and time. Monitoring also helps identify training needs by revealing recurring issues or misunderstandings. It can be carried out through direct observation, record reviews, audits, or automated systems such as instrument logs or QC software. This is especially critical in laboratories with multiple staff, where consistent practices in areas like biosafety, quality control, and data collection are vital. While SOPs define what should be done, procedure monitoring ensures it is done, consistently, correctly, and safely.

Tetraphenylethene maleimide (TPE-MI) is a fluorogenic, cysteine-reactive probe used to measure the accumulation of unfolded proteins and quantify proteostasis stress in live cells. TPE-MI is non-fluorescent until it reacts with exposed, reduced thiol residues on cysteine side chains. Upon binding, it fluoresces, providing a direct, quantitative measure of protein damage and aggregation, which can be monitored as an increase in median fluorescence intensity (MFI).

The hallmark cells of classical Hodgkin lymphoma (cHL) are Reed-Sternberg cells. These are large, often binucleated or multinucleated neoplastic B cells with prominent nucleoli. Their characteristic immunophenotype distinguishes them from normal lymphocytes and other hematologic cells. Pelger-Huët cells are hyposegmented neutrophils (and occasionally eosinophils) seen in Pelger-Huët anomaly, Mott cells are plasma cells filled with immunoglobulin inclusions, and Hand-Schüller-Christian cells are Langerhans cells seen in Langerhans cell histiocytosis; none of these display the Reed-Sternberg immunophenotype or are associated with cHL.

Laser power is typically measured using a laser power meter, which quantifies the output of the laser at a specific wavelength, with the measurement reported in milliwatts (mW). This measurement is performed by placing the sensor of the power meter in the laser beam path, usually at the laser's output or after it has passed through the optical system. Whichever location is chosen for measurement, it is important to keep it consistent for longitudinal measurements to ensure accurate comparisons over time. Some flow cytometers have built-in diagnostics to estimate laser power, but direct measurement with a power meter provides the most accurate assessment.

Scattering patterns and intensities provide information on the physical properties, composition, and morphology of the particles being studied.
Despite scatter parameters offering insights into sample health, including the presence of debris and pattern shifts indicating cell death, they fall short as reliable indicators of viability. For an accurate assessment of viability, it is recommended to employ specific reagents, such as DNA or amine-reactive dyes.

Only instruments equipped with either large-bore fluidics or specialized microfluidic pathways can accommodate small model organisms, large cells, cell clusters, seeds, pollen, and sizable particles such as beads, which are utilized as micro-carriers or for peptide libraries.

Digitization - transforming continuous analog voltage signals into discrete digital values (1s and 0s). The signal is digitized by measuring the height of the pulse at set intervals of time to derive the area (sum of all height values)

Binning - assigning the voltage pulse data: height, width, and area for each cell, to a bin, based on their value. An ADC with higher resolution offers a greater number of bins, enabling a more accurate and realistic distribution and display of data during analysis.

While surfactants effectively minimize bubbles within tubing, it is worth noting that sheath fluid incorporating these agents may generate more foam when splashed or shaken.

While many keywords use the $ sign (i.e., $CYT, $ETIM, $PnV…), keywords may also have the # prefix (i.e., #FLOWRATE, #PTRESULT) or no prefix at all (i.e., DURTIM, LASERxDELAY, THRESHOLD…). The syntax and naming conventions of keywords vary depending on the manufacturer of the instrument.

EDTA or EGTA chelates divalent cations, which may be present in biological samples or residual from sample preparation, thereby disrupting cell-cell adhesion. DNase I degrades extracellular DNA that can cause cell clumping and increase sample viscosity; however, its enzymatic activity is optimal in the presence of calcium and magnesium, so effectiveness is reduced in calcium- and magnesium-free conditions. Serum or conditioned media provide essential nutrients, supporting cell health and viability.

The Safe High Voltage or SHV is used for the high-voltage input connection to the PMT. Its design prioritizes safety, preventing accidental shocks or arcing under high voltage. The Bayonet Neill-Concelman or BNC is a type of coaxial connector used for the anode output signal. It provides a reliable connection for transmitting the electrical signal from the PMT to the measurement electronics. While BNC is more common, SMA connectors can be found on some PMTs, especially in applications where size is a constraint.

An LED is a semiconductor device that emits wavelength-specific light when an electric current passes through it. These devices are energy efficient and produce minimal heat.

Traditionally, samples are liquefied using a reducing agent such as dithiothreitol (DTT) in temperature-controlled conditions. This approach can negatively affect surface marker availability as well as cell viability and functionality, and may struggle to appropriately liquefy highly viscous samples.

Any disturbances or irregularities in the fluidic system of a flow cytometer have the potential to affect laser delays. Because these factors directly affect the timing of particle arrival at the laser beam, the laser delays initially calculated during instrument setup can become inaccurate.

Laser delays are set before the experiment begins and are not adjusted dynamically during acquisition. Changes in sheath velocity can render these delays incorrect, potentially leading to drops or losses of signals from specific laser lines. Extreme sample concentrations and cell clumping might also disrupt the timing of interrogation, causing signal instability. An increase in signal over time could indicate dye carryover from previous samples, such as DNA intercalating dyes. Additionally, wide temperature fluctuations beyond the instrument's operating range can affect signal detection. The signals generated by certain flow cytometers with open architecture can be affected by changes in ambient lighting.

Shared Resource Laboratories are not permitted to use their internal operating surplus or other recharge center to purchase new instruments. The acquisition cost of new equipment must be covered through approved and compliant funding sources. Acceptable methods include: (1) recovering equipment depreciation through user fees, where accumulated depreciation credits may be used toward future acquisitions; (2) institutional or other non-federal funding; (3) shared instrumentation grants or similar grant programs that support core facilities (though equipment purchased with federal funds cannot be depreciated again in core rates); (4) program income from NIH grants, when applicable; and (5) leasing or renting equipment as an alternative to outright purchase. These mechanisms ensure transparency, compliance, and sustainability in funding core infrastructure.

Carbonic anhydrase (CA) is an enzyme present in mature adult red blood cells. Pairing anti-HbF with anti-CA allows differentiation between fetal (HbF⁺, CA⁻) and adult (HbF⁻, CA⁺) red blood cells in maternal circulation. This combination is important because HbF is not exclusive to fetal cells; a small percentage of adult red blood cells, called F cells, also contain HbF. Using both reagents ensures accurate quantification of true fetal cells, which is particularly valuable in feto-maternal hemorrhage studies for clinical management and determining the correct dose of Rh immunoglobulin. By contrast, CD71 (transferrin receptor) is expressed on immature red blood cells, regardless of whether they are fetal or adult in origin, and therefore cannot reliably distinguish fetal from adult cells.

Operational Qualification (OQ) verifies that an instrument performs according to vendor specifications under expected operating conditions. This includes evaluating automated system functions, such as startup procedures and quality control routines, to ensure the system is working as intended. OQ also involves intentionally stressing the system to confirm it appropriately detects and reports errors (e.g., low sheath fluid, full waste container, disconnected software dongle, or triggered laser interlock), verifying that proper alerts are triggered. Additionally, optical precision is assessed by running calibration beads to ensure parameters like %rCV, detector sensitivity (Q & b), delta PMT voltages, and laser power output meet the manufacturer’s standards. If applicable, automated sample acquisition via a plate loader should also undergo random acquisition testing in replicates to verify consistency and reliability. These steps ensure the system's functionality is robust and dependable before it is released for routine use. Of note, the system’s dimensions are a parameter considered during Installation Qualification (IQ), as they relate to space requirements.

Neutrophils have reduced stability in fresh samples due to their short lifespan, susceptibility to activation, apoptosis, and sensitivity to variations in temperature, pH, and handling conditions. As a result, cryopreservation for delayed analysis is impractical, necessitating immediate processing. Additionally, neutrophils subjected to density gradient centrifugation exhibit notable activation and degranulation, accompanied by a low recovery rate.
Staining whole blood for 30 min at 4 °C, followed by a wash step to remove unbound antibodies and treatment with a combined fixation and red blood cell lysis step minimizes neutrophil activation, degranulation, and aggregate formation.

21 CFR Part 11 applies to organizations involved in regulated activities such as drug development, manufacturing, therapies, and medical devices. These areas require strict controls over electronic records and signatures. In contrast, environmental testing laboratories and academic basic research typically do not fall under FDA regulatory oversight and therefore are not generally subject to Part 11 requirements.