Estimation of Lipoprotein Ratios and Fractions

Used in MPhil thesis calculations and analysis [Population Variation for Risk Factors in Ischaemic Heart Disease, 1992].

Estimation of LDL-cholesterol (LDLc) using the Friedwald Formula. [Friedwald, W. T. et al. Estimation of the concentration of low density lipoprotein cholesterol without use of the preparative centrifuge. ClinChem. (1972), 18 (499-502].

Original Friedwald Formula (FF) = LDLc, mmol/L = TC – HDLc – (TG x 0.45).  LDL-c, mg/dL = TC – HDLc – (TG x 0.20).

Estimation of total cholesterol (TC) = TC = VLDLc + LDLc + HDLc.

Lipid Classification – total lipids cholesterol (HDL + LDL) + triglycerides  (VLDL).  Measurements of these cholesterol fractions can be obtained by knowing two of them from the following formula:

LDL = TC – TG/5 – HDL (in mmols).  [See : Graham, M.  (1988). The Effects of Cholesterol.  The Physician].

Also – LDLc = TC – HDLc – TG/2.19 (mmols).  [See:  Day, R. et al. (1989).  Treatment for hypertriglyceridaemia – state of the art.  Card in Pract. Feb].

Modification of the original FF.  See: DeLong D. M. et al.  (1986). A comparison of methods for the estimation of plasma low- and very low-density lipoprotein cholesterol.  JAMA 256 (11). Nov.

The DeLong modification of FF. LDLc, mmol = TC – HDLc – (TG x 0.37).   LDLc, mg/dL = TC – HDLc – (TG x 0.16).

They concluded that LDLc was better estimated using the following formula:

LDLc = TC – (LDLc + 0.16 x TG). mmols.   Or:  LDLc = TC – (HDLc + 0.37 x TG).  mg/dL.

This proposed formula is more precise for plasmas or sera with a TG concentration within the normal range.

Thus the original FF = plasma TG in mgms/L is determined and an estimate of VLDLc in mgms/L is made by: dividing TG by 5 (i.e E-VLDLc = 0.20 TG), (0.46 in mmols). DeLong called estimated VLDLc – E-VLDLc.

Therefore – estimation of E-VLDLc = E-LDLc = TC – (HDLc + E-VLDLc) = TC – (HDLc + 0.20 X TG)

Modification of the original FF using an intercept: the linear regression coefficient for VLDLc on TG and the intercept.

See: Rao, A. et al.  (1988).  Calculation of low-density lipoprotein cholesterol with use of triglyceride/cholesterol ratios in lipoproteins compared with other calculation methods.  Clinical Chemistry.  34 (12).

Therefore – LDLc mmol/L = TC – HDLc – (TG x 0.342) = 0.118.  Also – LDLc mg’dl = TC – HDLc – (TG x 0.148) + 4.6.

Using an FF that varies with TG: FF was found to correlate significantly with TG. (FF = 0.47 – (0.022 x TG).

Therefore – LDL mmol = TC – HDLc – TG = [0.47 – (0.022 x TG)].  Thus – LDL mg’dl = TC – HDLc – TG = [0.022 – 0.00011 x TG)].

Rao, A. et al (1988).

 

 

 

 

 

 

 

To be continued

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One response to “Estimation of Lipoprotein Ratios and Fractions

  1. Pingback: Interpreting Your lipoprotein Test - Health Education Care

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