Why would a person need a serum apolipoprotein b measurement?

Not a routine test: The general consensus is that apolipoprotein b levels do not provide more information than LDL levels. The exception being rare metabolic disorders.

To Assess Therapy: Ldl can be estimated by ldl-c or measured by particle number (apob or NMR ldl-p). When ldl-c and ldl-p disagree (due to cholesterol variability per particle) cvd risk tracks with LDL particle number. In addition to ldl-c and non-hdl-c (total cholesterol minus hdl-c) goals, expert panel recommendations advise if apob or ldl-p is elevated treatment should be changed to reach an apob or ldl-p target.

Metabolic syndrome: Patients with obesity, Insulin resistance , pre- diabetes and metabolic syndrome often have normal LDL cholesterol levels wi low HDL and high tg's these patients have increases apo b due to tg flux into LDL from vldl with the generation of increased numbers of small dense LDL particles and elevated apob levels not predicted by LDL and non-hdl . Much data: several groups & countries recommend this.