Apolipoprotein A-I

Updated: Jul 07, 2021
Author: Georges Elhomsy, MD, ECNU, FACE; Chief Editor: Eric B Staros, MD 

Reference Range

Apolipoprotein A-I (Apo-A1) is a structural and functional protein that constitutes approximately 70% of the protein in high density lipoprotein (HDL).

The reference ranges of Apo-A1 are as follows[1] :

  • Adult males: 75-160 mg/dL
  • Adult females: 80-175 mg/dL
  • Male newborns: 41-93 mg/dL
  • Female newborns: 38-106 mg/dL
  • Males (aged 6 months-4 years): 67-167 mg/dL
  • Females (aged 6 months-4 years): 60-148 mg/dL
  • Children aged 5-17 years: 83-151 mg/dL


Low apolipoprotein A-I level

A low Apo-A1 level indicates an increased risk of cardiovascular disease, especially in the presence of an elevated apolipoprotein B (Apo-B) level.[2, 3, 4, 5]

Other factors that are associated with low Apo A1 level include the following:

  • Chronic liver disease

  • Chronic kidney disease

  • Smoking

  • Obesity

  • High triglyceride level

High apolipoprotein A-I level

High Apo-A1 levels are associated with the following:

  • Pregnancy

  • Alcohol use

  • Spring and summer seasons[6]


Collection and Panels

Patient instructions: Overnight fasting (12-14 hours)

Collection tube: Lavender top (EDTA)

Unacceptable conditions: Hemolyzed specimens

Specimen preparation: Separate serum from cells as soon as possible or within 2 hours of collection and transfer to 1-mL serum transport tube

Storage/transport temperature: Refrigerated

Stability refrigerated: 8 days unfrozen; 3 months frozen

Panels: None

CPT Code: 82172




Apolipoprotein A-I (Apo-A1) is a structural and functional protein that constitutes approximately 70% of the protein in HDL.

Apo-A1 is produced in the liver and intestines and activates lecithin-cholesterol acyltransferase (LCAT) in the peripheral tissues, which transforms free cholesterol to cholesterol ester and facilitates its transportation to the liver, were it is degraded.


Because it is not clear whether Apo-A1 is an independent predictor of cardiovascular disease, it may be useful for Apo-A1 to be measured in conjunction with Apo-B to assess the Apo-B/Apo-A1 ratio.

A higher ratio means an increased likelihood of cholesterol deposition in arteries, leading to atherosclerosis and a higher risk of cardiovascular disease.

A prospective cohort study by Xiao et al indicated that as a risk factor, the Apo-B/Apo-A1 ratio is more strongly associated with abdominal aortic aneurysm (AAA) then with coronary heart disease (CHD), despite the relationship of both conditions to atherosclerosis. In addition, Apo-A1 was found to have a greater protective effect against AAA than CHD.[7]

A study by Henson et al indicated that in patients with coronary artery disease, low levels of immune complex consisting of Apo-A1 and immunoglobulin G (IgG) are an independent risk factor for adverse cardiovascular events. Thus, according to the investigators, this immune complex may represent a potential biomarker for predicting cardiovascular disease progression.[8]

Apo-A1 is one of many serum markers used in the fibroTest, a noninvasive assessment of the liver that was validated in many liver disease, including hepatitis C, hepatitis B, nonalcoholic fatty liver disease, and alcoholic liver disease.


Serum Apo-A1 is not considered a routine test for cardiovascular disease risk assessment.

Overnight fasting might not be necessary to evaluate apo-A1, but most of the laboratories still commend it.

Apo-A1 Milano is a naturally occurring mutant of Apo-A1 associated with a very low HDL level but apparent longevity and much less atherosclerosis than expected for their HDL-C levels.[9]

A defect in the Apo-A1 gene (APOA1) can cause HDL deficiency and systemic nonneuropathic amyloidosis.


Questions & Answers