Lipemia: The Optical Illusion That Breaks Assays

We love our Schnauzers, but we don't love their lipemic blood.

Lipemia (high triglycerides) turns plasma from clear yellow to milky white. In cfDNA testing, this is a major interference, particularly for the most common method of measurement: Fluorometry.

How Fluorometry Works

Labs use tools like the Qubit or specialized plate readers to measure cfDNA concentration. They mix the plasma with a dye (like PicoGreen or SYBR Gold). This dye inserts itself between the DNA base pairs and glows (fluoresces) when hit with light. The machine measures the brightness of the glow to calculate the DNA amount.

The Lipemia Effect

Lipid droplets in the plasma scatter light.

1. Quenching: The lipids can block the light, making the sample appear dimmer than it is. (False Low).
2. Autofluorescence: Sometimes, lipid complexes and proteins can fluoresce on their own or scatter light in a way that mimics signal. (False High).
3. Extraction Failure: If the lab uses spin columns (little silica filters) to purify the DNA, heavy lipids can clog the filter membrane, causing the DNA to be lost during the wash steps.

Managing the Milky Sample

Prevention is key:
* Fast the patient: A 6-hour fast clears most post-prandial lipemia.
* High-Speed Spin: The "Double-Spin" protocol is your friend here. When you spin plasma at 16,000 x g, the lipids often stratify to the very top (a white creamy layer), while the clear plasma sits in the middle, and cell debris is at the bottom.
Technique: Carefully pipette from the middle* of the tube, punching through the lipid layer if necessary (or aspirating it off first) to get the clear plasma.

If the sample is opaque like heavy cream, the lab will likely reject it. It is better to reschedule the draw than to pay for a guess.