Lipämische Probe

A lipämische Probe is a sample in which the serum or plasma, once the cells have been separated, appears cloudy to milky instead of clear straw yellow. The cause is a high concentration of triglyceride rich particles suspended in the liquid phase.

Three ordinary situations produce that appearance in a sample:

• The person ate shortly before the appointment and a fat containing meal is still circulating, which is the most common reason by far.
• A metabolic condition produces the same appearance without any recent meal.
• Certain medications produce it too, and then it does not depend on the last meal at all.

That is the reason Nüchternheit is asked for at all, because where a laboratory requests a fasting sample the request is often less about the analyte itself than about keeping the sample readable.

Someone who arrives after breakfast has done nothing wrong, but the appointment can produce a sample the laboratory cannot report in full, so the draw then has to be repeated. Asking the fasting question when the appointment is booked, and confirming it at the counter, costs nothing and prevents that repeat.

The turbidity interferes with a measurement in two ways. Many methods read light through the sample, and suspended fat scatters that light, so photometric readings come out wrong. The particles also take up volume in the liquid phase, which distorts measurements that assume a normal water content.

Which analytes are affected, and at what point a result is suppressed rather than released with a comment, depends on the analyser and the method. That decision belongs to the laboratory, which measures the turbidity as an index rather than judging it by eye.

For a pharmacy the practical consequence is narrow, because nobody at the counter inspects a tube and concludes anything from how it looks. The remark comes from the laboratory, on the report, as a technical observation about the specimen.

Together with Hämolyse it belongs to the small group of findings that describe the sample rather than the person, so the handling is the same in both cases. The comment is passed on as it was written, the fasting question is checked before any repeat is arranged, and any explanation of what a persistently milky sample might mean belongs to a physician.

In Präanalytik terms only three things are within the pharmacy's control:

• The instruction given when the appointment is booked can state the fasting requirement.
• The appointment can be timed before the person has eaten that day.
• Prompt separation and transport get the sample to the laboratory in the condition it left in.

A value released with a lipaemia comment also deserves particular care when it is close to a Referenzbereich limit, because the comment is the laboratory stating that this number is less certain than usual.