F. Obtain a Fasting Lipid Profile

objective

Screen appropriate patients for the presence of dyslipidemia.

background

Lipid levels are preferably obtained in a fasting state.  However, if the testing opportunity is nonfasting, only the values for TC and HDL will be usable.  In otherwise low-risk persons (0–1 risk factor), further testing is not required if the HDL-C level is > 40 mg/dL and TC is <200 mg/dL.  For persons with multiple (2+) risk factors, LDL-C levels are needed as a guide to clinical management.

The most common method for assessing serum lipid levels involves measuring TC, HDL-C and TG levels and then using the Friedewald formula to calculate the LDL-C [LDL =TC – HDL – (TG/5)].  TG concentrations, however, are affected by recent food intake and will affect the calculation of LDL-C (see Annotation G).  Although nonfasting values may still provide useful information, treatment of dyslipidemia requires measurement of lipids in the fasting state.  Therefore, patients should be fasting for at least 9-14 hours prior to lipid profile determinations to ensure an accurate LDL-C value.

recommendations

1. A complete fasting lipid profile should be obtained in an individual with other risk factors for coronary disease.  [A]
2. Clinical decisions should be based upon lipid profiles done 1 to 8 weeks apart (fasting) with an LDL-C or TC difference of <30 mg/dL.  [I]
3. Lipid profiles should not be obtained within 8 weeks of acute hospitalization, surgery, trauma, or infection unless they are obtained within 12-24 hours of the event to ensure accuracy.  [I]
4. Lipid profiles should not be measured in pregnant women until three to four months post partum.  [I]

discussion

LDL-C is routinely estimated from measurements of TC, TG, and HDL-C in the fasting state.  If the TG level is below 400 mg/dL, this value can be divided by five to estimate the VLDL-C level. Since TC is the sum of LDL-C, HDL-C, and VLDL-C, a calculated level of LDL-C can be estimated by using the Friedewald (1972) formula as follows:
LDL-C = TC – HDL-C – TG/5 (Friedewald et al., 1972).

Intra-individual cholesterol measurement may vary up to 14 percent from an individual’s average value (Cooper et al., 1992).  The standard deviation of the differences in measured cholesterol values increases as the average cholesterol level increases.  Therefore, some guidelines recommend that clinical decisions should be based upon lipid profiles done 1 to 8 weeks apart (fasting or no fasting) with an LDL-C or TC difference of less than 30 mg/dL.  If the second result differs by more than 30 mg/dL, repeat again or calculate the average of the results.

Measurement of any lipid is preferably performed with the patient in a baseline stable condition, in the absence of acute illness.  Recent acute hospitalization, MI, stroke, surgery, trauma, or infection may temporarily lower cholesterol levels up to 40 percent.  Some medications can have an incidental negative impact on a patient’s lipid profile.  Progestins, estrogens, androgens, anabolic steroids, corticosteroids, cyclosporine, diuretics, protease inhibitors, and retinoids may raise cholesterol and/or TG levels.

If a lipid profile cannot be obtained immediately (within 12 to 24 hours of the event), a lipid profile can be obtained no less than 8 weeks post-event to obtain an accurate reading.  Cholesterol levels increase by as much as 20 to 35 percent during pregnancy and should not be measured until three to four months after delivery.