R&D Systems Quantikine ELISA Operation Guide

critical

Absent Standard Curve Signal with Normal Zero Standard

No detectable signal is observed for standard curve points containing analyte, while the zero standard (maximum binding control) shows normal OD values, indicating complete loss of competitive inhibition.

💡 4 · ✓ 4

critical

No Signal or Weak Signal in ELISA

The ELISA plate reader detects no colorimetric signal or signal intensity is significantly below expected values after substrate development. Wells appear clear or only faintly colored even after standard incubation times of 10-30 minutes.

💡 6 · ✓ 6

critical

No Signal for Standard Curve with Normal Zero Standard

All standard concentrations show no signal (high OD in competitive format similar to zero standard), while the zero standard (no competitor) shows normal maximum binding signal.

💡 4 · ✓ 4

critical

Complete Absence of Standard Curve Signal with Normal Zero

All standard concentrations show no detectable signal (very low OD), while the zero standard (B0, maximum binding) produces normal expected signal, indicating complete competition failure.

💡 4 · ✓ 4

severe

Excessive Non-Specific Background Signal in Competitive ELISA

High background optical density readings are observed across wells, obscuring the difference between standards and samples. Signal persists even in wells without primary antibody or sample.

💡 4 · ✓ 4

severe

B/B0 Ratio Outside Acceptable Range at Curve Endpoints

The B/B0 ratio (bound/maximum bound) for the terminal point of the standard curve is either >95% or <5%, indicating insufficient competitive displacement range.

💡 3 · ✓ 3

severe

Insufficient Signal from Zero Standard (B0)

The zero standard (no competing antigen, maximum antibody binding) produces OD values that are too low, resulting in compressed standard curve with poor sensitivity.

💡 4 · ✓ 4

severe

Standard Curve Plateau at High Concentration Range

The standard curve reaches a plateau (flat response) at high standard concentrations with correspondingly low OD values, failing to show expected dose-response relationship in competitive ELISA format.

💡 4 · ✓ 4

severe

Non-specific Background Signal Too High in Competitive ELISA

High background optical density is observed across wells, reducing signal-to-noise ratio and making it difficult to distinguish specific binding from non-specific interactions.

💡 4 · ✓ 4

severe

Standard Curve Plateau at High Concentration End

The standard curve reaches a plateau at high analyte concentrations (low OD values in competitive format), showing no further decrease in signal despite increasing standard concentration.

💡 4 · ✓ 4

severe

OD Value of Zero Standard Too Low

The zero standard (maximum binding, no competitor) shows insufficient optical density signal, providing inadequate dynamic range for the competitive assay and poor B/B0 calculations.

💡 4 · ✓ 4

severe

Primary and Secondary Antibody Incompatibility

No signal or minimal signal in indirect ELISA despite proper coating and blocking. Positive controls with matched antibodies work correctly.

💡 4 · ✓ 4

severe

Antibody or Reagent Loss of Activity from Improper Storage

Progressive signal loss over time using the same reagents. Previously working protocols suddenly fail. Positive controls that worked before now show reduced or no signal.

💡 5 · ✓ 5

severe

High CV from Inconsistent Pipetting Technique

High intra-assay coefficient of variation (>15%) between technical replicates. Standard curve shows poor reproducibility between duplicate points.

💡 5 · ✓ 5

severe

Standard Curve R² Below 0.98 Threshold

The regression coefficient (R²) of the standard curve falls below 0.98, indicating poor curve fit and unreliable quantification of sample concentrations.

💡 5 · ✓ 6

severe

Serial Dilution Calculation or Execution Error

Standard curve shows irregular pattern or non-monotonic response, with individual points deviating significantly from expected sigmoidal or linear trend.

💡 5 · ✓ 6

severe

B/B0 Ratio at Curve Endpoint Outside 5-95% Range

The B/B0 ratio (bound/maximum bound signal) for the highest or lowest standard concentration exceeds 95% or falls below 5%, indicating the standard curve dynamic range does not adequately cover the analyte concentration range.

💡 4 · ✓ 4

severe

High Non-Specific Background Signal in Competitive ELISA

Elevated background signal is detected across wells, interfering with specific signal measurement. Background noise reduces assay sensitivity and may mask low-concentration analyte detection.

💡 4 · ✓ 4

severe

High Inter-Assay CV from Inconsistent Sample Storage

High inter-assay coefficient of variation (>15%) when the same samples are tested across different runs. Sample readings decrease over time or vary unpredictably between runs.

💡 5 · ✓ 5

severe

Incomplete Standard Reconstitution with Visible Particulates

After adding reconstitution buffer to lyophilized standard, visible undissolved material or particulates remain in the vial, leading to inaccurate standard concentrations.

💡 4 · ✓ 6

severe

Low OD Value for Zero Standard in Competitive ELISA

The zero standard (B0, representing maximum antibody binding without competing analyte) produces lower than expected optical density values, reducing overall assay sensitivity and dynamic range.

💡 4 · ✓ 4

severe

High CV from Inconsistent Well Washing

High coefficient of variation (>15%) between replicates with uneven background signal across the plate. Some wells show higher background than others after washing steps.

💡 5 · ✓ 5

severe

Inadequate Blocking of Non-Specific Binding Sites

Uniformly elevated background across plate with high coefficient of variation. Background may be particularly high in wells with lower antigen concentrations.

💡 4 · ✓ 4

severe

High Variability Between Replicates (CV >15%)

Replicate wells for the same sample or standard show high coefficient of variation (>15%), with inconsistent absorbance values that suggest uneven treatment or technical errors.

💡 5 · ✓ 5

severe

High Uniform Background Signal

All wells show elevated absorbance including blanks and negative controls, creating a uniformly high background that reduces signal-to-noise ratio and compresses the standard curve.

💡 5 · ✓ 5

moderate

Standard Curve Plateau at High Concentration End

The top of the standard curve (high analyte concentration, low OD) shows a plateau with minimal signal change across multiple high-concentration standards, reducing dynamic range.

💡 4 · ✓ 4

moderate

Wrong Instrument Settings for Detection Wavelength

No signal or very low signal readings from plate reader despite visible color development or expected fluorescence. Signal does not correlate with visual observations.

💡 4 · ✓ 4

moderate

Mixed Components from Different ELISA Kits

Unpredictable or absent signal despite following protocol. Results are inconsistent and do not match expected standard curves. Signal may vary dramatically between experiments.

💡 4 · ✓ 4

moderate

Incubation Temperature Below Optimal Range

Consistently weak signal across all samples including positive controls. Signal improves when experiment is repeated with attention to temperature. Longer incubations partially compensate.

💡 4 · ✓ 4

moderate

Over-Washing Removes Bound Detection Reagents

Signal progressively decreases with increased wash steps or aggressive washing. Reducing wash stringency restores signal. Edge wells show lower signal than center wells.

💡 4 · ✓ 5

moderate

Excessive Substrate Concentration or Incubation Time

Rapid color development with all wells turning dark quickly. Signal may exceed linear range of reader (OD >2.0). Background wells show significant color development.

💡 4 · ✓ 5

moderate

High CV from Bubbles in Wells

Inconsistent absorbance readings between replicate wells with coefficient of variation >15%. Visual inspection may reveal bubbles present in wells, particularly when using detergent-containing solutions.

💡 4 · ✓ 4

moderate

Unexpected or Inconsistent Assay Results

Sample quantification values are outside expected biological range, controls fail to meet acceptance criteria, or results are not reproducible between runs despite similar experimental conditions.

💡 5 · ✓ 5

moderate

Biological Sample Not in Detectable Range

Standard curve appears normal, but sample wells show no signal or signal below the lowest standard. This occurs when the analyte concentration in samples is below the assay detection limit.

💡 4 · ✓ 4

moderate

High Variability Between Experimental Runs

Standard curves or sample values differ significantly between experiments run on different days, despite using the same reagents and protocol, showing poor reproducibility.

💡 5 · ✓ 5

moderate

Edge and Drift Effects on ELISA Plate

Wells at the plate edges show systematically higher or lower absorbance than center wells, or a gradient pattern appears across the plate, affecting data quality especially for samples in edge positions.

💡 5 · ✓ 5

moderate

Standard Curve Fitting Model Not Appropriate

The recommended curve-fitting model (typically Four-Parameter Logistic) does not adequately fit the standard data points, resulting in poor correlation even with properly prepared standards.

💡 4 · ✓ 5

moderate

B/B0 Ratio at Standard Curve Endpoint Out of Range

The B/B0 ratio (bound/maximum bound) at the lowest or highest standard concentration is either >95% or <5%, indicating the standard curve dynamic range is not properly positioned.

💡 3 · ✓ 3

moderate

Bacterial Contamination in Wash or Incubation Buffers

Sporadic signal loss or high background that worsens over time during multi-day experiments. Cloudy or turbid buffer appearance. Inconsistent results when using same buffer batch.

💡 4 · ✓ 5

moderate

High CVs at Bottom of Standard Curve

Coefficient of variation (CV) among replicates is excessively high at the lowest standard concentrations (highest OD in competitive format), reducing precision at the sensitive end of the curve.

💡 4 · ✓ 4

moderate

High Coefficient of Variation Between Standard Replicates

Duplicate or triplicate wells for the same standard concentration show high variability (CV >10-15%), compromising curve fit and confidence in quantification.

💡 5 · ✓ 6

minor

Sample Values Above Assay Range (Hook Effect Excluded)

Sample absorbance readings exceed the top standard, reading off the curve, while the standard curve itself appears normal with proper shape and dynamic range.

💡 2 · ✓ 3

minor

Green Color Upon Adding Stop Solution (Streptavidin-HRP)

When sulfuric acid stop solution is added to wells after TMB substrate incubation, a green color appears instead of the expected yellow, indicating incomplete mixing and pH gradient in the well.

💡 2 · ✓ 3