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Clarification Methods

Why is Lipemia a cause for concern in Clinical Chemistry?

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

Other known factors related to the cause of lipeamia are

Light Scatter

Lipemia &

Lipemic Index

  • diabetes mellitus,
  • alcohol abuse,
  • hypothyroidism,
  • pancreatitis;
  • drug induced such as oral contraceptives
  • in the treatment of lipophilic drug overdose

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

Volume Displacement

An increased concentration of lipids results in serum volume with decreased water content and excludes electrolytes into the aqueous portion of serum. As electrolytes are not found in the lipid portion procedures that measure electrolytes in total serum volume (per unit of serum which includes the lipid fraction)

e.g. flame photometry or indirect potentiometry will result in falsely decreased electrolyte volume.

Interference Studies and Index Establishment

What is Lipemia?

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)

What Causes Lipemia?

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

Mercy Hospital 2014

Can Lipemia be Avoided?

How is Lipemia Quantified and Interference Levels Defined?

What is Intralipid?

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