Multiplex assay detection limits: how low can cytokines be measured?

When researchers ask about multiplex assay detection limits, they are usually asking a very practical question: Will this assay detect the cytokines in my samples, or will my results come back below range?

That question matters because cytokines are often present at very low concentrations, especially in serum, plasma, cerebrospinal fluid, healthy donor samples, early-stage disease models, or low-inflammatory conditions. In some studies, the expected cytokine signal may be in the low pg/mL range. In others, it may be below that. In highly stimulated cell culture supernatants or acute inflammatory samples, cytokine concentrations may be much higher.

• Many multiplex cytokine assays can measure cytokines in the low pg/mL range, and some platforms can reach even femtogram-level sensitivity for selected analytes. But there is no single universal detection limit for cytokines or other analytes. The real limit depends on the analyte, assay platform, sample type, matrix effects, and whether the value being discussed is a limit of detection or a limit of quantification.

At Eve Technologies, we provide multiplex cytokine, chemokine, and biomarker testing services using established platforms such as Luminex and MSD. With more than two decades of multiplex assay experience and services cited in over 4,000 published articles, our team supports academic researchers, biotechnology companies, pharmaceutical programs, CROs, and clinical research teams with assay services designed to make cytokine testing more accessible, efficient, and interpretable.

What does detection limit mean?

A detection limit tells you how little of an analyte an assay can “see.” But in cytokine testing, the phrase detection limit is often used loosely. To understand cytokine assay sensitivity, it helps to separate three related terms.

Limit of blank, or LoB	The limit of blank is the highest apparent signal expected from a sample that does not contain the analyte. In simple terms, it is the background noise of the assay.
Limit of detection, or LoD	The limit of detection is the lowest concentration that can be distinguished from the blank. If a cytokine signal is above the LoD, the assay may be able to detect that it is present. But detection is not the same as reliable quantification.
Lower limit of quantification, or LLOQ	The lower limit of quantification is the lowest concentration that can be measured with acceptable precision and accuracy. For most research studies, this is often more important than LoD.

A value between LoD and LLOQ may be detectable, but it may not be reliable enough to report as a precise concentration. A value above the LLOQ is more useful because it falls within the assay’s quantifiable range. Analytical guidance distinguishes LoB, LoD, and LoQ because they describe different levels of confidence in low-concentration measurement.

A simple way to think about it:

Result range	What it means	How to interpret it
Below LoD	The assay cannot reliably distinguish the signal from background	Treat as not detected or below detection limit
Between LoD and LLOQ	The analyte may be detectable, but not reliably quantified	Use caution; this is not ideal for precise comparisons
Above LLOQ	The analyte can be quantified within the validated range	Best range for statistical analysis and biological interpretation
Above ULOQ	The analyte is above the upper quantifiable range	Dilution may be needed, depending on the assay

This is why a very low LoD can look impressive on a datasheet but still not guarantee usable study data. For decision-making, researchers should ask: What percentage of my samples are expected to fall above the LLOQ?

How low can cytokines actually be measured?

The short answer is: often low pg/mL on standard multiplex platforms, and lower than that on some ECL or ultrasensitive systems, but not equally for every cytokine. In Bio-Rad’s public 48-plex performance table, many inflammatory targets sit in the sub-pg/mL to low-single-digit pg/mL range, though some analytes have higher published LoDs [3]. By contrast, MSD’s public S-PLEX human proinflammatory panel 1 shows median LLODs from 8.0 to 43 fg/mL across a representative 9-plex panel [4]. That is a major reason why MSD is so often selected when the target cytokines are expected to be scarce in serum or plasma. Quanterix and other ultrasensitive vendors push selected markers even lower, but those formats usually trade away plex breadth. In practice, the right answer is never just “what is the best listed LoD?” but “what platform will quantify the cytokines likely to exist in my matrix at my expected biological range?”

1. Luminex and bead-based multiplex assays

Luminex-style bead-based multiplex assays are widely used for broad cytokine, chemokine, and growth factor profiling. Their major strength is the ability to measure many analytes from a small sample volume.

For many cytokines, bead-based multiplex assays operate in the low pg/mL range, although the exact lower limit depends heavily on the analyte and the kit. Thermo Fisher’s current FLEXMAP 3D instrument specifications list immunoassay sensitivity as 0.06–1 pg/mL, while clearly noting that this is assay-dependent. A 48-plex, 71-plex, or 96-plex panel does not have one detection limit. Each cytokine has its own antibody pair, calibration curve, background, dynamic range, LoD, and LLOQ.

Luminex-based multiplexing is often a strong choice when:

Study need	Why Luminex may fit
You need broad immune profiling	Many cytokines can be measured together
Sample volume is limited	Multiple analytes can be measured from one sample
You are exploring pathways	Broad panels help identify unexpected immune signals
Expected cytokine levels are low to moderate pg/mL or higher	Many analytes may fall within useful detection ranges

At Eve Technologies, Luminex-based Discovery Assays are especially useful for exploratory biomarker studies where researchers want broad cytokine coverage without purchasing full plates for every project.

2. MSD electrochemiluminescence assays

MSD assays use electrochemiluminescence technology and are often selected when researchers need strong low-end sensitivity, broad dynamic range, or focused multiplex panels for low-abundance biomarkers.

Study need	Why MSD may fit
Cytokine levels are expected to be very low	fg/mL detection for selected targets
You need stronger low-end quantification	Lower LLOQs may reduce below-range results for some analytes
You are working with challenging matrices	Electrochemiluminescence can provide low background
You need focused panels rather than very high plex	MSD panels are often lower-plex than broad Luminex panels

However, MSD is not automatically better for every analyte or every sample type. The best platform is not just the one with the lowest number on a datasheet. It is the one that can quantify the cytokines you care about in the sample type you actually have.

3. ELISA

ELISA is a familiar and widely used immunoassay format. It is often reliable, accessible, and useful when measuring one specific cytokine. However, traditional ELISA is usually a single-analyte method, meaning each cytokine typically requires its own assay well or plate.

In terms of sensitivity, ELISA should be discussed carefully. It is common to say that ELISA is less sensitive than multiplex platforms, but that is not always accurate.

Conventional colorimetric ELISA is often less sensitive than MSD or ultrasensitive platforms, and it is much less efficient when many cytokines need to be measured. But high-sensitivity ELISA kits can be very sensitive for selected single targets.

4. Ultrasensitive cytokine platforms

Some cytokines are difficult to measure because they circulate at extremely low concentrations. In those cases, researchers may need ultrasensitive technologies.

For example, Quanterix lists its Simoa IFN-γ Advantage Assay Kit with a lower limit of detection of 0.015 pg/mL, or 15 fg/mL LoD. [6]

Ultrasensitive assays can be valuable when the biological question depends on measuring very low-abundance cytokines. However, they are not automatically the best choice for every study. Researchers still need to consider assay availability, target list, sample type, matrix validation, cost, throughput, and whether they need one marker, a focused panel, or broad immune profiling.

Luminex vs MSD: when and why to choose each

For customers deciding between Luminex and MSD, the choice is usually about breadth versus low-end confidence. Luminex is the better first choice when you want broad immune profiling, especially in exploratory studies where you need 30, 48, or even more cytokines from limited sample. Our test menu reflects that strength: broad Discovery Assays, species-specific panels, and public options such as HD48A, HD48B, and HD96 are built for discovery-stage profiling from small sample volumes. If your study is trying to map a cytokine landscape, classify immune phenotypes, or generate a first-pass signature, Luminex is usually the most practical place to start. 

MSD is the better choice when the study question is narrower but the analytes are harder to measure. In the peer-reviewed comparison from Günther and colleagues [7], MSD delivered lower LLoQs than the Luminex-format assay for 14 of 16 overlapping cytokines. Platchek and colleagues similarly reported that MSD had the strongest low-end sensitivity and broadest dynamic range among the tested methods[8]. That is why MSD is often the better answer for baseline cytokines, minimally inflamed samples, translational studies where subtle changes matter, and validation work where below-LLoQ values would undermine the study.

Luminex usually gives the best cost-per-data-point for broad discovery panels, while MSD is the better value when low-abundance measurement is the main technical risk. Eve’s public materials reinforce that distinction: its Discovery Assays are marketed as cost-efficient, pay-per-sample or pay-per-well services for broad multiplexing, while its MSD service is positioned around higher sensitivity rather than maximum plex size.

Why cytokine detection limits vary so much

1. The cytokine itself

Some cytokines are naturally present at higher concentrations. Others circulate at very low levels unless there is strong immune activation.

For example, cytokines such as IL-6, IL-8, MCP-1, and VEGF may be easier to detect in many inflammatory settings than cytokines that are often very low in circulation, such as IL-2, IL-4, IL-10, or IL-12p70.

This is why you can run a well-established panel and still see some analytes below detection. That does not necessarily mean the assay failed. It may mean the biology is below the assay’s quantifiable range.

2. Sample type

Sample matrix matters. Serum, plasma, cell culture supernatant, CSF, tissue lysate, lavage fluid, and other matrices can behave very differently.

Cell culture supernatants from stimulated cells may contain cytokines at easily measurable concentrations. Healthy human plasma may contain many cytokines near or below the assay’s detection limit.

Serum and plasma can also produce different results because clotting, anticoagulants, matrix proteins, and processing conditions can affect measured concentrations. Current assay manuals and modern bioanalytical guidance emphasize that matrix effects, dilution, recovery, and precision should be evaluated carefully when working near the lower end of an assay range.

3. Matrix effects

A matrix effect happens when components of the sample interfere with the assay signal. This can suppress or enhance the measured concentration.

In cytokine work, matrix effects are especially important near the lower detection limit because a small change in background can determine whether a result is measurable or below range.

This is one reason a kit may perform well in standards or assay buffer but behave differently in serum or plasma.

4. Sample handling

Cytokine measurements can be influenced by pre-analytical factors such as sample collection, processing time, storage temperature, and freeze-thaw history. These effects can vary by cytokine, sample matrix, and assay platform, but they are especially important when working near the lower end of an assay’s measurement range. [9], [10]

What improves multiplex cytokine assay sensitivity in practice

If your goal is improving assay sensitivity, the biggest gain usually comes from choosing the right platform first. If you expect analytes to cluster near the blank, a broad bead-based panel may give you excellent multiplexing but insufficient low-end confidence. If your study needs only a more focused panel and the cytokines are expected at very low abundance, platforms with lower reported assay floors are often the better fit. That is a design decision, not a rescue step after data come back. 

After platform selection, preanalytics matter. de Jager and colleagues reported major stability issues for many cytokines after repeated freeze-thaw cycles, and manufacturer protocols reinforce the same point: aliquot early, avoid repeated thawing, remove particulates, and avoid heavily hemolyzed or lipemic samples. For matrix-heavy samples, it is also important to validate dilution and ensure calibrators and controls behave similarly to the actual specimen matrix. That is especially important when you are working near the lower limit of detection cytokines can achieve on paper, because small handling errors can erase the apparent sensitivity advantage of a kit. 

For service providers and CRO-style partners, the most trustworthy way to communicate multiplex cytokine assay sensitivity is to separate three questions: what the kit reports, what the matrix allows, and what the study actually needs. Customers appreciate that distinction because it turns a vague sensitivity claim into a credible study-design recommendation.

Run a pilot when the answer is uncertain

If expected concentrations are unknown, a pilot study can be very useful. Testing a small number of representative samples first can show whether the chosen panel is likely to produce measurable data before committing the full study.

A pilot can help answer:

• Which analytes are above LLOQ?
• Which are consistently below range?
• Are sample dilutions appropriate?
• Is the matrix compatible with the assay?
• Should a more sensitive platform be used for selected markers?

This is often the most practical way to avoid choosing a platform based only on theory.

Choosing the right platform and designing a pilot study

Platform selection should begin with the biological objective, not a generic sensitivity ranking.

Decision question	Why it matters	Likely direction
Which cytokines are essential to the primary hypothesis?	Critical analytes should drive sensitivity requirements	Review analyte-specific LLOQ, not only panel size
Are expected concentrations known in the same species and matrix?	Published values from another matrix or assay may not transfer	Use preliminary samples when uncertainty is high
Is the study exploratory or hypothesis-driven?	Discovery rewards breadth; confirmation may reward focused sensitivity	Broad Luminex/MSD panel versus focused ELISA or ultrasensitive assay
How much sample is available?	Running many single-analyte ELISAs can rapidly consume specimens	Multiplexing becomes more valuable as target count rises
What percentage of results can be below LLOQ before the study loses value?	A low detection rate can undermine statistics and interpretation	Define an analyte-specific target before testing
Is a wide concentration range expected?	Inflammation cohorts can include baseline and highly elevated samples	Consider dynamic range and dilution strategy as well as LLOQ
Is the work exploratory research or regulated bioanalysis?	Validation depth and acceptance criteria differ	Align the validation plan with intended use

Practical recommendations

• Prioritize LLOQ over headline LoD. LoD indicates that the assay may distinguish a low signal from background. LLOQ indicates that the concentration can be reported with defined precision and accuracy.

• Review every critical analyte separately. A 10-plex, 48-plex, or larger panel does not have one universal detection limit. The least suitable analyte may determine whether the panel meets the study objective.

• Use matrix-specific information. Performance in calibrator diluent does not prove performance in serum, EDTA plasma, heparin plasma, CSF, tissue lysate, or cell-culture medium.

• Treat sample dilution as part of sensitivity. The effective biological threshold depends on the assay LLOQ and the sample dilution required to control matrix effects.

• Standardize sample handling. Use consistent collection tubes, processing intervals, centrifugation, aliquoting, storage, and freeze-thaw history. Avoid assigning study groups to different processing batches where possible. 

• Do not switch platforms casually. Absolute concentrations can differ substantially even when two assays are nominally measuring the same cytokine. A platform change can complicate longitudinal or cross-study interpretation. 

Frequently asked questions

What is the difference between LoD and LLoQ?

LoD is the lowest concentration distinguishable from background. LLoQ is the lowest concentration that can be quantified with acceptable precision and accuracy. For study design, LLoQ is usually the more actionable number (Armbruster & Pry, 2008, Clinical Biochemist Reviews). 

Is plasma or serum better for cytokine measurement?

Neither is universally best, but matrix choice matters. Multiplex studies have shown that serum can suppress readout more than plasma for some cytokines, and plasma is often preferred for low-abundance targets when the assay and study design support it (Rosenberg-Hasson et al., 2014, Immunologic Research). 

When should I choose Luminex instead of MSD?

Choose Luminex when you need broad profiling, efficient use of small sample, and good cost-per-data-point for discovery-stage work. Choose MSD when a smaller set of cytokines must be quantified with stronger low-end sensitivity. That is the clearest customer-facing distinction. 

Does Eve Technologies offer both broad and high-sensitivity testing?

Yes. We offer Discovery Assays and custom multiplex panels on both Luminex and MSD.

What is the fastest way to improve cytokine assay sensitivity?

Match the platform to expected abundance first, then standardize matrix, minimize freeze-thaw cycles, and follow strict sample-handling controls. Those changes usually matter more than minor downstream data-processing tweaks. 

If your study needs broad cytokine discovery, customized analyte selection, or higher-sensitivity confirmation of low-abundance biomarkers, Eve Technologies can help map the biology to the right assay format. Whether that means a Luminex-based Discovery Assay, a Custom Plex panel, or an MSD workflow built for more difficult targets. The right service decision is about choosing the platform that will quantify the cytokines your samples are actually capable of producing. 

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References

1. Clinical and Laboratory Standards Institute (CLSI). Evaluation of Detection Capability for Clinical Laboratory Measurement Procedures. CLSI guideline EP17. Clinical and Laboratory Standards Institute. https://clsi.org/
2. International Council for Harmonisation / European Medicines Agency. ICH Q2(R2): Validation of Analytical Procedures. Scientific guideline. https://www.ema.europa.eu/en/ich-q2r2-validation-analytical-procedures-scientific-guideline
3. Bio-Rad Laboratories. Bio-Plex Pro Human Cytokine, Chemokine, and Growth Factor Assays. Manufacturer instruction manual and assay documentation. Link.
4. Meso Scale Discovery. S-PLEX Proinflammatory Panel 1 Human Kit. Manufacturer product information and assay performance specifications. Link.
5. Thermo Fisher Scientific. Luminex FLEXMAP 3D Instrument System. Manufacturer platform specifications for multiplex immunoassay applications. Link.
6. Quanterix. Simoa IFN-γ Assay Kit. Manufacturer assay specifications for ultrasensitive cytokine measurement. Link.
7. Günther A, Becker M, Göpfert J, Joos T, Schneiderhan-Marra N. Comparison of Bead-Based Fluorescence Versus Planar Electrochemiluminescence Multiplex Immunoassays for Measuring Cytokines in Human Plasma. Front Immunol. 2020 Sep 24;11:572634. doi: 10.3389/fimmu.2020.572634. PMID: 33101295; PMCID: PMC7546899.
8. Platchek M, Lu Q, Tran H, Xie W. Comparative Analysis of Multiple Immunoassays for Cytokine Profiling in Drug Discovery. SLAS Discov. 2020 Dec;25(10):1197-1213. doi: 10.1177/2472555220954389. Epub 2020 Sep 13. PMID: 32924773.
9. Platchek M, Lu Q, Tran H, Xie W. Comparative Analysis of Multiple Immunoassays for Cytokine Profiling in Drug Discovery. SLAS Discov. 2020 Dec;25(10):1197-1213. doi: 10.1177/2472555220954389. Epub 2020 Sep 13. PMID: 32924773.
10. Liu C, Chu D, Kalantar-Zadeh K, George J, Young HA, Liu G. Cytokines: From Clinical Significance to Quantification. Adv Sci (Weinh). 2021 Aug;8(15):e2004433. doi: 10.1002/advs.202004433. Epub 2021 Jun 10. PMID: 34114369; PMCID: PMC8336501.