[Hypocholesterolemias: causes and diagnosis].

Most of the hypocholesterolemias in adults and children are presented and the non-cardiovascular risk of low serum cholesterol (cancer, depressive illness.) is discussed. A good assessment of hypocholesterolemia is provided by usual laboratory lipid tests (total, HDL- and LDL-cholesterol, apolipoproteins B and A1) and completed by lipid assays of parents in case of familial diseases. The diagnosis of secondary hypocholesterolemias is easy in well-known causes (liver diseases, hyperthyroidism, digestive malabsorption) but less obvious in other cases (fever, traumatism, inflammatory disease); nevertheless, it is necessary to avoid expensive laboratory investigations which will be reserved for severe familial hypocholesterolemias (in order to improve the treatment and the knowledge of these rare diseases); however diagnosis fails in some well-tolerated familial cases.