Methods include :
1 - Ultracentrifugation (e.g. Airfuge) 90,000rpm ~ 20psi for ~15mins (Gold Standard)
2 - High Speed centrifugation ~ 13,000 rpm or higher for 15 mins, infratatant (clearer lower fraction) transferred to a new tube and re centrifuged
3 - Lipid Clearing Agent such as Lipoclear used at 1 part per 9 parts sample
Lipemia is a potential cause of analytical interference; it may cause false low or false high results due to
(1) light Scatter or
(2) volume displacement
Optical interference causing measurement errors in photometrical methods (end point, rate, nephelometric or turbidimetric) due to light scatter and absorption of the light by the lipids (mainly chylomicrons and very low density lipoproteins
Lipemia is the presence of a fine emulsion of fatty substance in the blood
It is characterised by turbidity of samples which may range from slightly opaque through transparent, turbid to milky appearance
Patient samples are spiked with varying concentrations of intralipid
The concentration at which the interference occurred is determined by plotting the measured analyte value against the interference concentration
A recovery difference > 10% from the non-spiked sample was deemed to be significant interferance
These interfering concentrations are then established into indices
To truly assess the extent of the lipid interference, a mechanism to remove or minimise the lipid concentration is required,
Para physiological: IV administration of lipids such as TPN for nutritional need in critically ill patients
Metabolic Disturbances: Diseases where the liver is unable to remove the chylomicrons from blood (e.g. Hypertriglyceridemia)
Ultracentrifugation is considered to be the gold standard of clarification methods
A final triglyceride concentration of < 15 mmol/L in a cleared sample is preferable
Unfortunately these methods are not available here in the mercy
Lipemia can originate from physiological, Para physiological causes as well as metabolic disturbances
Physiological: Post prandial Metabolism, lipemia can be caused by a rise in chylomicrons following a meal with a high fat content
Mairead Keating
Lipemic Index are quantitative estimates of turbidity that can be spectrophotometrically detected in a sample and expressed in ordinal values (+1, +2 etc.) or actual concentration units
Interference studies due to lipemia are not easily performed as it is difficult to obtain suitable material to mimic lipid interference
Most manufactures establish lipemic index by interference experiments using intralipid supplemented sample.
Manufacturers often provide guidelines for the maximum acceptable lipemia that have been established by interference experiments.
This index is known as Lipemia Index or LI
Intralipid is a fat emulsion containing soy bean, egg yolk phospholipids and glycerine, it consists predominantly of small relatively dense, phospholipid rich liposomes and triglyceride rich artificial chylomicrons and no complex mixture of lipoproteins
Lipids in patient samples are far more complex than intralipid and due to the composition differences there is poor association between lipaemic index and triglyceride concentration.
Triglycerides are usually the most abundant lipids in lipemia
A relatively low lipemic index may have a high triglyceride concentration
In some cases Lipemia can be avoided simply by having the patient fast for 8 hours prior to the samples being drawn
In disease processes where the liver is unable to remove the chylomicrons from the blood, the appearance of lipemic serum may be unavoidable.
In such cases other method may be used. These include Direct ISE measurement to compare indirect ISE measurements and mechanisms to remove or minimise the lipid concentration such as clarification