What is the role of lab testing in the workup of low LDL cholesterol syndromes?

Updated: Mar 06, 2018
  • Author: Vibhuti N Singh, MD, MPH, FACC, FSCAI; Chief Editor: George T Griffing, MD  more...
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Answer

Laboratory studies include the following:

  • Routine complete blood cell count with differential, including platelet count - Some patients present with thrombocytopenia. In the absence of another obvious explanation, a low platelet count may be considered secondary to vitamin cofactor malabsorption, and one must consider the possibility of abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL).

  • Blood smear to assess erythrocyte morphology - Acanthocytosis (burr cells) may be evident in patients with FHBL, but even when the erythrocytes appear normal, an exceptionally low sedimentation rate can be demonstrated. Patients with ABL uniformly demonstrate acanthocytosis. From 40-80% of erythrocytes are acanthocytic. Mild to moderate anemia with mild to moderate reticulocytosis may also be present.

  • Basic chemistry (metabolic) panel - This test is used to exclude multisystem illness or evidence of malnutrition from another cause.

  • Liver function tests, including transaminases - Hepatic transaminases have been reported to be elevated in patients with ABL and FHBL. The mechanism for this finding is unclear. [20]

  • Stool studies - Search the stool for ova, parasites, and white blood cells in order to exclude other common causes of fat malabsorption.

  • Fasting lipid profile - A fasting lipid profile should be obtained from patients and their first-degree relatives, in the latter case to assist in distinguishing between ABL and homozygous FHBL. The parents of a patient with ABL have normal cholesterol levels, while the parents of a patient with homozygous FHBL have lower-than-average cholesterol levels.

    • Heterozygous FHBL - Patients with heterozygous FHBL may have total cholesterol levels that are below the fifth percentile (and may be less than 100 mg/dL). Plasma low-density lipoprotein (LDL) cholesterol levels are also reduced by one half or more. High-density lipoprotein (HDL) cholesterol levels are normal or slightly increased. Plasma triglyceride levels are reduced in some kindreds.

    • Homozygous FHBL - Patients with homozygous FHBL show extremely low plasma cholesterol and triglyceride levels.

    • ABL - Characteristically, extremely low levels of plasma cholesterol (< 50 mg/dL) and triglycerides are detected in infants and young children. Patients who are obligate heterozygotes have normal cholesterol levels.

  • ABL or homozygous FHBL diagnosis - This depends on finding acanthocytes in the peripheral blood and extremely low plasma levels of cholesterol (< 50 mg/dL). Chylomicrons (CMs) and very low-density lipoprotein (VLDL) are not detectable, and LDL is virtually absent.


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