Most of what I have read is in synch with WebMD's take:

The normal range for apolipoprotein B is less than 90 milligrams per deciliter, or mg/dL, of blood. If you receive normal test results, you have appropriate amounts of lipoproteins in your blood and your risk for heart disease is low.

Abnormal results can mean a few things.

High levels of apoB. ApoB-100 levels measuring above 110 milligrams per deciliter are high. If your test results show a higher-than-normal rate, you have a higher-than-normal risk for heart disease.

Some underlying conditions can cause high apoB levels, including:

Underactive thyroid

Kidney disease

Diabetes

Pregnancy, which causes temporarily high levels