The way we measure omega-3 levels in the blood—like using plasma versus red blood cells—can change how clearly we see the effects of certain genes on those levels.

What we've found so far is that the type of blood sample used to measure omega-3 levels may influence how strongly we can detect genetic effects on those levels. Our analysis of the available research suggests this is a factor worth considering when interpreting study results. We reviewed 20.0 studies or assertions that support the idea that the method of measuring omega-3s—such as using plasma versus red blood cells—can affect how clearly genetic links appear [1]. None of the evidence we analyzed refuted this idea. This means that depending on which part of the blood is tested, researchers might see stronger or weaker connections between specific genes and omega-3 levels. For example, red blood cells reflect longer-term omega-3 status, while plasma may show more short-term changes. Because of these differences, the same gene might appear more influential in one type of sample than another. Our current analysis shows that the choice of blood sample type could shape what researchers observe when studying genetic influences. This doesn’t mean one method is better—it means they may provide different insights. We don’t yet know how much this affects overall conclusions about which genes matter most, but it does suggest that comparing studies using different sample types requires caution. There isn’t enough evidence to say how large this effect is or which sample type gives the most useful picture for everyone. But based on what we’ve reviewed so far, the evidence leans toward the idea that sample type matters when studying gene-omega-3 relationships. Practical takeaway: If you're looking at genetic tests or studies about omega-3s, pay attention to how omega-3 levels were measured—results might look different if they used plasma instead of red blood cells.