How to Reduce Sample Interference in CLIA Assays Effectively

You run the assay. The values come back off. Not catastrophically wrong, just inconsistent enough to make you doubt everything. You’ve checked the protocol twice. The kit hasn’t expired. But the CV is terrible.

Sample interference is one of the most common and least discussed causes of poor results in chemiluminescent immunoassay (CLIA) Kits. It doesn’t announce itself. It just quietly ruins your data.

If you’re dealing with this right now, you are not alone. Here’s how to find it and fix it.

What Does Sample Interference Actually Look Like?

It rarely looks like a blunt failure. The signal is still there. The controls pass. But your unknowns show unexpected patterns, results that spike in one replicate and collapse in another, or values that trend in the wrong direction compared to your standard curve.

The culprit is usually something in the sample matrix that either competes with your target analyte, cross-reacts with the antibody, or quenches the chemiluminescent signal itself. Common offenders include hemoglobin, lipids, bilirubin, rheumatoid factor, and heterophilic antibodies.

Spike a known concentration of your analyte into the problematic sample matrix. If you get poor recovery (below 80% or above 120%), interference is almost certainly your problem.

My Samples Are Hemolyzed. Does That Really Affect CLIA Results?

Yes, more than most people realize. Hemoglobin and heme-containing compounds absorb light across a broad spectrum. In a Chemiluminescent Immunoassay (CLIA) test, even moderate hemolysis can reduce the signal and lead to lower results.

The fix isn’t just “don’t use hemolyzed samples.” In clinical or animal study work, that’s sometimes not an option. Instead:

Dilute the sample further into the linear range of the assay, if your analyte concentration permits.

Always include a matrix-matched blank so you can subtract background from each sample type. Use the kit’s recommended diluent instead of PBS or water to keep results consistent.

Heterophilic Antibodies Are Easy to Miss

This one trips up even experienced labs. Heterophilic antibodies, including human anti-mouse antibodies (HAMA), can bridge the capture and detection antibodies in a sandwich CLIA format. This creates a false-positive signal that has nothing to do with your analyte.

If you’re working with human serum samples and seeing anomalously high values in a sandwich format, add a heterophilic antibody blocking reagent to your diluent.

What About Lipemic or Icteric Samples?

Lipemic (high-fat, turbid) and icteric (high-bilirubin, yellowish) samples are common preanalytical issues. Also, they’re part of the HIL profile that the researcher uses to assess sample quality. Both can change your results if they are not handled properly, basically in light-based assays.

What’s the Issue with These Samples?

Lipemia scatters light and reduces signal accuracy, while icterus (high bilirubin) affects signal detection or disturbs the antibody-antigen binding. This can give lower results than expected.

How Do You Detect These Interferences?

Try to identify whether a sample contains excess lipids or bilirubin that could affect your results. Visual inspection can give a clue (milky for lipemia, yellow for icterus), but it’s not very reliable. If possible, use analyzer-based serum indices for a more accurate assessment.

How to Handle Lipemic Samples

The main problem is excess lipids interfering with signal detection.

What you can do: A high-speed centrifugation step (10,000–15,000 × g for 10 minutes at 4°C) helps remove much of the lipid fraction. It won’t eliminate interference, but it typically improves signal recovery to an acceptable range.

How to Handle Icteric Samples

The issue here is that high bilirubin affects the performance of the assay.

What you can do: Dilution is usually the simplest approach. Just make sure to run a parallelism check. Serially dilute the sample and confirm that it follows your standard curve. This ensures your results are still reliable.

A Few Things Worth Standardizing Immediately

Beyond the specific fixes above, sample interference compounds when collection and handling aren’t consistent. These three practices help across all sample types:

1. Standardize your collection tube type: EDTA plasma, heparin plasma, and serum behave differently. Heparin, in particular, can inhibit enzyme-based detection systems. Use the matrix type validated by the kit manufacturer.
2. Keep freeze-thaw cycles to a minimum: Each cycle degrades some analyte and can concentrate matrix contaminants. Aliquot samples before freezing.
3. Equilibrate samples to room temperature before use: Cold samples pulled straight from the freezer can cause condensation and microdroplet variation that looks like interference but is actually a temperature effect.

Final Thought

Sample interference is solvable. It just requires being systematic, ruling out the most common causes one at a time, rather than changing everything at once and losing track of what actually worked.

Choosing a well-validated kit is part of the equation, too.