How FH is Diagnosed: Testing and Screening

Diagnosing Familial Hypercholesterolemia (FH) is a multi-step process that combines physical exams, family history, and high-tech lab work ^[1]. Because this condition starts at birth, finding it early through standardized screening is the most powerful way to protect your heart health ^[2].

When and How Children are Screened

Many medical guidelines recommend that children have their cholesterol checked at specific ages, regardless of whether they seem healthy or have a family history of heart disease ^[3]. Note that screening guidelines can vary by country and region.

• Universal Screening: In the US, for example, guidelines suggest all children should have a lipid panel (cholesterol test) between the ages of 9 and 11, and again between 17 and 21 ^[3][4].
• Targeted Screening: If a child has a parent with known FH or a family history of early heart attacks, screening can start as early as age 2, though most specialists begin around age 5 ^[5][6].
• Early Screening for HoFH: If a child shows physical signs like yellowish skin bumps (xanthomas) or if both parents have high cholesterol, testing should happen immediately, even in infancy ^[5][7].

The Three Pillars of Diagnosis

Doctors use three main pieces of information to confirm a diagnosis, ruling out other causes of high cholesterol (like hypothyroidism or kidney disease) along the way:

1. LDL Cholesterol Levels: Under certain guidelines, an LDL-C level of 160 mg/dL or higher (with a family history) or 190 mg/dL or higher (without a known family history) serves as a decision threshold to evaluate for FH ^[5]. If a parent has a known genetic mutation, the threshold for evaluating the child may drop to 130 mg/dL ^[8].
2. Genetic Testing: A blood or saliva test looks for mutations in the LDLR, APOB, or PCSK9 genes ^[9]. Finding a pathogenic (disease-causing) mutation confirms a molecular diagnosis and helps predict how the condition might progress ^[10].
3. Family History: Doctors look for “premature” heart disease in the family—usually defined as a heart attack or stroke before age 55 in men or age 65 in women ^[5][11].

Why Genetic Testing Matters

While a simple cholesterol test can show the “what,” genetic testing shows the “why.” It is often recommended even if the LDL level is already known because it provides information that a standard blood test cannot ^[9]:

• Prognosis: People with a confirmed pathogenic genetic mutation often have a higher cardiovascular risk compared to those with high cholesterol from lifestyle factors or multiple minor genes (polygenic high cholesterol) ^[9][12].
• De Novo Mutations: In rare cases, a child may have FH even if neither parent does. These are called de novo mutations, where the gene change happens for the first time in that individual ^[13]. Relying only on family history would miss these cases.

However, keep in mind that a negative genetic panel does not rule out FH; testing can miss certain variants, or the condition may be polygenic. Also, a variant of uncertain significance is not a confirmed diagnosis. A genetic counselor can help you interpret these nuances.

Cascade Screening: Protecting the Whole Family

Once one person (the “index case”) is diagnosed with FH, it is critical to perform cascade screening. This is a systematic process of testing close biological relatives ^[10].

For the most common form (typical HeFH, an autosomal dominant trait), every first-degree relative (parent, sibling, or child) of a person with FH has a 50% chance of inheriting the same pathogenic variant ^[10][14]. Note that inheritance patterns for HoFH or recessive forms are different.

The process typically works like this:

1. Test First-Degree Relatives: Parents, brothers, sisters, and children are tested using both a lipid panel and a test for the specific familial mutation (if known) ^[15].
2. Reverse Cascade: If a child is the first one diagnosed, the parents and their siblings should be tested immediately. This often uncovers adults who have lived with undiagnosed FH for decades ^[16][17].
3. Continue the Chain: If a sibling is found to have FH, the screening then moves to their children and other close relatives ^[16].

Using the specific familial mutation makes this process highly accurate. However, relatives who test negative for the familial pathogenic variant still need to have routine lipid screening as they can still have high cholesterol from other causes ^[10][18].