Measurement of sterols is important in the diagnosis and monitoring of a patient with sitosterolemia.
Plant sterols are not detected by methods used to measure blood cholesterol. If plant sterols are not measured then the diagnosis may be missed or delayed.
Method: chromatography (gas, gas plus mass spectrometry, high pressure liquid)
Sterols that can be measured include:
(1) sitosterol
(2) campesterol
(3) stigmasterol
Reasons for a low sitosterol concentration in a patient with sitosterolemia:
(1) low sterol diet
(2) therapy with ezetimibe or cholestyramine
Reasons for a false positive result:
(1) infants may show a transient increase in plasma sterol concentration based on diet and metabolic maturation.
(2) parenteral nutrition
The plasma level of sitosterol can also be interpreted relative to the total cholesterol concentration.
ratio of sitosterol to cholesterol =
= (plasma sitosterol in mg/dL) / (plasma total cholesterol in mg/dL)
Interpretation:
• Normally the concentration of plasma sterols is very low.
• With sitosterolemia the plasma sitosterol concentration is > 1 mg/dL.
• The ratio of sitosterol to the upper limit of normal is often high (>30 or more).
• The trajectory of plasma sitosterol over time can be used to monitor therapy.
• The ratio of sitosterol to total cholesterol is elevated in sitosterolemia and an elevated ratio is associated with increased atherosclerosis.
