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

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

Buffer Components Inhibit Detection Enzyme

No or very weak signal despite correct antibody binding. Signal loss occurs after addition of detection reagent. Other wells using different buffers show normal signal.

💡 4 · ✓ 4

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

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

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

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 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

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

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

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

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