Lipid Panels, Atherosclerosis, and Electrolyte Exclusion Effects

Flashcards covering lipid profiles, fasting requirements, atherosclerosis pathology, LDL and non-HDL calculations, pseudohyponatremia, and direct versus indirect ISE sodium analysis.

What is the historical fasting duration required for a routine lipid profile?

$12$ to $14\text{ hours}$.

What is the primary vascular role of high-density lipoprotein (HDL)?

It pulls plaque away from the arteries, acting as the "good" cholesterol.

Why is low-density lipoprotein (LDL) referred to as the "bad" cholesterol?

It deposits in arterial walls, leading to atherosclerosis and the narrowing of arteries.

What dietary lipid particles are eliminated from circulating blood when a patient fasts?

Chylomicrons.

What should be done when a refrigerated chemistry sample presents with a floating white scum on top?

Warm the sample up to room temperature before analysis so that the white scum goes back into solution.

In a routine laboratory setting, which lipid parameter is typically calculated rather than measured directly?

LDL (low-density lipoprotein).

What are the primary physiological roles of cholesterol described in the lecture?

Maintaining membrane integrity and supporting hormone production.

What is the physiological role of triglycerides, and what occurs during insulin deficiency?

They act as energy storage. When insulin is deficient (such as in type 1 diabetes), triglycerides are broken down for energy, resulting in weight loss and ketone formation.

Between cholesterol and triglycerides, which is least affected by diet and which is most affected?

Cholesterol is least affected by diet, whereas triglycerides are most affected.

What cellular process leads to myocardial infarction following plaque rupture in an artery?

Platelets adhere to plug the breached plaque wall, which can completely occlude the artery, blocking red blood cells and oxygen delivery to cardiac tissue.

What does the term "atherogenic" mean?

Promoting or leading to the deposition of plaque in the arteries.

What is the Friedewald formula for calculating LDL using SI units?

$$\text{LDL} = \text{Total Cholesterol} - \text{HDL} - \frac{\text{Triglycerides}}{2.2}$$

At what triglyceride concentration does the Friedewald LDL calculation become invalid?

When triglycerides are greater than $4.51$.

What is the formula for calculating non-HDL cholesterol, and when is it most clinically useful?

$\text{Non-HDL Cholesterol} = \text{Total Cholesterol} - \text{HDL Cholesterol}$; it is useful for assessing atherogenic cholesterol when a patient did not fast.

What does the term "pseudohyponatremia" mean?

A falsely lowered sodium level.

What is the electrolyte exclusion effect in lipemic samples?

Excess lipids displace aqueous plasma volume (analogous to a sumo wrestler displacing rubber duckies in a tub), falsely decreasing measured electrolyte concentration in indirect methods.

What distinguishes indirect ion-selective electrode (ISE) measurement from direct ISE measurement?

Indirect ISE requires a sample dilution (such as a $1\text{ in }33$ dilution), whereas direct ISE measures the sample without applying a dilution.

Which sodium measurement method is susceptible to pseudohyponatremia caused by lipemia?

Indirect ISE systems (direct ISE systems are unaffected).

What is the reference range and critical threshold for serum sodium stated in the lecture?

The reference range is $135$ to $145\,\text{mmol/L}$, and the critical threshold is less than $120\,\text{mmol/L}$.

What corrective procedure should be performed to measure sodium in a lipemic sample using an indirect ISE analyzer?

Ultracentrifuge the sample at a high RPM to precipitate the fat, pipet off the cleared plasma/serum, analyze it, and append an ultracentrifugation comment.

Why is it mandatory to document that a sample has been ultracentrifuged?

To ensure that future add-on test requests for lipids or triglycerides are not performed on a fat-depleted sample.

If an ultracentrifuge is unavailable, how can a valid sodium result be obtained for a lipemic sample?

Analyze the sample using a direct analysis platform, such as a blood gas analyzer.

Why should a technologist avoid ultracentrifuging a sample prior to analyzing it on a direct measurement system?

Because direct measurement is not affected by lipemia, so ultracentrifugation unnecessarily prolongs turnaround time.