Diagnosing ABL: Understanding Your Lab Results

Diagnosing abetalipoproteinemia (ABL) requires a combination of specialized blood tests and genetic analysis. Because ABL is so rare, your doctor will look for a very specific pattern in your lab results—one that shows your body is unable to effectively produce the “transport ships” (lipoproteins) needed to move fats and vitamins ^[1][2]. Your doctor will also rule out secondary causes of very low cholesterol, such as malnutrition, hyperthyroidism, or advanced liver disease.

The Core Lipid Markers: LDL and apoB

The most striking feature of ABL is extremely low levels of cholesterol and certain proteins in the blood. Two markers are especially important clinical clues:

• LDL-C (Low-Density Lipoprotein Cholesterol): Often called “bad cholesterol,” this is usually very low or even undetectable in ABL. Diagnostic guidelines often look for levels below 15 mg/dL ^[1][2].
• Apolipoprotein B (apoB): This is the structural protein needed to build fat-transporting containers. In ABL, apoB levels are typically below 15 mg/dL or completely absent ^[1][2].

While these numbers (below 15 mg/dL) are highly suggestive in the right clinical context, they are not absolute diagnostic cutoffs and can vary with age and laboratory methods ^[3].

Examining Your Blood Under a Microscope

One of the unique signs of ABL is found by looking at your blood cells under a microscope, a test called a peripheral blood smear.

In some cases (reported around 58% in a review), patients have acanthocytosis ^[4]. This means your red blood cells look “spiky” or “thorny” instead of smooth and round ^[5][6]. These spikes occur because the lack of fats in your blood changes the structure of the red blood cell’s outer “skin” (membrane) ^[6]. While it is a variable morphological clue rather than a strict requirement—and it does not inevitably cause anemia—finding them is a major clue for your medical team ^[4].

The Role of Genetic Testing

Genetic testing can help confirm a diagnosis of ABL. Your doctor will look for mutations in the MTTP gene ^[7].

To have ABL, you must have two mutations—one from each parent. This is called a biallelic mutation ^[1]. You might have the same mutation from both parents (homozygous) or two different mutations in the same gene (compound heterozygous) ^[7][8]. Confirming an MTTP mutation helps distinguish ABL from other conditions, like HoFHBL (caused by the APOB gene). However, a negative genetic panel doesn’t always definitively rule out ABL (as some complex variants can be missed), and a “variant of uncertain significance” requires careful interpretation by a genetic counselor ^[9][10].

Your Completeness Checklist

When reviewing your lab reports, ensure you and your doctor have discussed each of these key areas:

If any of these tests are missing from your records, it is worth asking your care team if they should be ordered to complete your clinical picture. Monitoring these labs regularly is a standard part of staying healthy with ABL ^[1].