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

After developing the ELISA plate, wells show no color change or very faint signal that is barely above background, even for positive controls or high-concentration standards.

💡 6 · ✓ 6

critical

No Signal or Weak Signal in ELISA

No detectable signal or very weak signal across all wells, including standard wells. The plate reader shows absorbance values near baseline or significantly lower than expected.

💡 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

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

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

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

High CV from Plate Edge Effects

Outer (edge) wells show systematically different absorbance values compared to inner wells, with CV >15%. Edge wells may show higher or lower signal depending on evaporation or temperature variation. Visual inspection from the side reveals lower buffer levels in edge wells.

💡 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

Poor Dynamic Range Between Signal and Background

The difference between maximum signal (high standards) and background (blank wells) is compressed, typically less than 5-fold, making it difficult to distinguish between samples of different concentrations.

💡 5 · ✓ 5

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

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

Uneven Color Development Across Plate

Color intensity varies significantly between wells that should be identical. Pattern may show edge effects, gradients across the plate, or random spotty appearance indicating incomplete or inconsistent reagent contact.

💡 4 · ✓ 4

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

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

Excessive Primary Antibody Concentration Saturating Wells

High background signal with poor signal-to-noise ratio. Standard curve may show compressed dynamic range or plateau at lower concentrations than expected.

💡 3 · ✓ 3

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

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