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356 Biochemical Evaluation of Dyslipidemia

Lipoprotein(a) (Lp[a]) similar to LDL and are syn- 4. C-reactive protein
thesized in the liver. Lp(a) differs from LDL by the 5. Cell adhesion molecules
addition of Apo(a), a protein with a structure that is
homologous to plasminogen. High levels of Lp(a)
are both prothrombotic and proatherogenic. Levels Special Investigations:
of Lp(a) in plasma are determined by genetic varia- 1.Measurement of Apolipoproteins may be required in
tion in the two Lp(a) alleles. While investigating dys- assessing vascular risk or for diagnosis of inherited
lipidaemia it is essential to consider those tests that deficiencies or excesses
are useful for routine CVD risk assessment as well 2.Tests are also required to rule out different types
as additional risk factors of primary hyperlipidaemias are useful in those with

While investigating lipid abnormalities the first step inherited hyperlipidaemia.
is to differentiate between primary and secondary In Type 1 hyperlipidaemia or Familial chylomicronae-
hyperlipidaemia and therefore the following should mia syndrome (FCS)
be considered
This is an autosomal recessive condition which is
-Tests to establish primary /secondary hyperlipidae- characterized by excessive circulating chylomicrons
mia due to defective or absent LPL activity, often calcu-
-Tests that establish additional risk lated LDL-C is not available ,when lipid profile is re-
quested in these subjects as the TG level is high and
-Lipid related
the Friedewald formula for calculating LDL-C is in-
-non- lipid related accurate. High TG levels interfere with measurement
of LDL-C and other analytes like sodium concentra-
The Following investigations are required to exclude tion depending on the method used. A simple test
secondary causes
involves placing the tube in which the blood sample
Urine dipstick test to rule out proteinuria, thereby ex- was centrifuged in a refrigerator, to demonstrate the
cluding nephrotic syndrome and some other forms creamy layer with a clear serum layer separating it
of renal disease from the red cells and can be called a ‘fridge test’
and is a very specific test with minimum cost.
Thyroid function tests to rule out hypothyroidism
Mass or activity measurement of LPL is rarely avail-
Liver tests (including gamma GT) to rule out liver dis- able in routine laboratories but may be requested
ease, excessive alcohol intake and primary biliary cir- from specialist centres. This measurement requires
rhosis. Further liver tests such as anti-mitochondrial administration of 60 to 100 IU of heparin/kg to mo-
antibody levels and other autoantibody screens may bilize the LPL bound to the endothelium.
be required
Genetic testing is available for the diagnosis of the
Glucose and glycated haemoglobin to rule out dia- condition. Additional proteins involved in LPL enzyme
betes
complex in lipolysis are Apo CII, Apo A5, Lipase
Protein electrophoresis may be required as the pres- Maturation factor 1 (LMF1) and glycosylphosphatidyl
ence of monoclonal proteins can raise TG concen- inositol anchoring high density lipoprotein binding
tration protein 1 (GPIHBP1). Mutations involving these pro-
teins `may result in excessive chylomicrons in the
Investigations that establish risk and diagnosis
circulation. Current recommendation is for full gene
Lipoprotein related Lipoprotein(a) sequencing of LPL and the genes for other 4 co-fac-
tors involved in lipolysis
Apoproteins: Type 2a hyperlipidaemia or familial hypercholestero-
apo B-100, A-I, CIII LDL particle size laemia in addition to lipoprotein (a) and a full lipid

Particle number Apo E genotype profile most international guidelines recommend ge-
netic testing that involves sequencing of LDL recep-
Nonlipid risk factors tor, Apo B and PCSK9 genes.
1. Homocysteine* Type 2b or familial combined hyperlipidaemia
2. Fibrinogen Genetic testing is not available. A nomogram includ-
3. Plasminogen activator inhibitor ing Apo B levels, total cholesterol and TG concentra-
tion for diagnosis of familial combined hyperlipidae-

GCDC 2017