Subclinical ADHD

Subclinical ADHD means that ADHD symptoms are present, but the threshold required for a diagnosis according to DSM or ICD has not been reached. Subclinical ADHD is not “non-existent ADHD”. It is ADHD that is more difficult to treat if the person with ADHD is suffering from it.

Since ADHD is not categorical but dimensional and, moreover, the degree of symptoms can fluctuate within a certain range even in the case of lifelong ADHD (“fluctuating ADHD” in 10 to 15 % of people with ADHD¹ ), it makes sense to take subclinical ADHD seriously and to document the diagnosis.

Differentiating subclinical ADHD from late-onset ADHD
Sometimes ADHD becomes “subclinical” simply because, contrary to the DSM requirement, no occurrence of several symptoms before the age of 12 can be documented or retrospectively (= in retrospect) determined. If in such cases the number of symptoms exceeds the threshold value at the time of diagnosis and the other secondary requirements of the DSM or ICD are also met, it is not subclinical ADHD, but late-onset ADHD.
In a study of 7 to 9-year-old children with subclinical psychiatric disorders, 37% developed a full-blown Disorder after 3 years.² The people with ADHD in this study had neither subclinical nor late-onset ADHD, but normal ADHD according to the DSM 5 criteria.
Unfortunately, the term late-onset ADHD is also used by many studies for cases in which individual symptoms were already present up to the age of 6 years (DSM IV) or 11 years (DSM 5) and only no full-blown ADHD was present. If a lack of a full picture up to this age is (in our opinion incorrectly) referred to as late-onset ADHD, there would need to be a different term to designate ADHD in which no symptoms or only one symptom was present up to the age of 6 (DSM IV) or 11 (DSM 5). More on this under Late-Onset ADHD: late-onset or late-diagnosed ADHD?

Subclinical ADHD is present if all DSM or IDC criteria are met with the exception of the number of symptoms at the time of diagnosis.
The updated European consensus on the treatment and diagnosis of ADHD from 2018 points out that studies are now available according to which, from a scientific point of view, a cut-off of 4 symptoms in adults would be more correct for a correct ADHD diagnosis.³⁴⁵

Some studies have attempted to measure the prevalence of subclinical ADHD. This is inherently complicated by the fact that no clear criteria have been established for subclinical ADHD.
More on this at Prevalence of subclinical ADHD in the article Frequency of ADHD (prevalence) In the chapter Diagnostics.

Subclinical ADHD is also associated with symptomatic and social limitations as well as increased comorbidities ⁷⁸

• Suicide
  • Suicidal plans were 54 times more common in people with ADHD and 18 times more common in subclinical ADHD than in people without ADHD. Suicidal thoughts were 12.8 times as common in those with ADHD and 8.3 times as common in those with subclinical ADHD as in those without ADHD⁹
• Addiction
  • Cannabis abuse was as high in subclinical ADHD as in clinical ADHD and significantly higher than in non-affected individuals¹⁰
  • Internet addiction was almost as high in subclinical ADHD as in clinical ADHD¹⁰
• Sleep
  • Sleep quality was significantly worse in subclinical ADHD than in non-affected people, although not as bad as in clinical ADHD¹⁰
• Quality of LIfe
  • Social quality of life was almost as severely impaired with subclinical ADHD as with clinical ADHD¹⁰
  • Quality of life for subclinical ADHD was in the middle between ADHD and non-affected people¹⁰
• Cognition
  • In subclinical ADHD, 23% had impairments in 3 or more cognitive domains, compared to 4% to 6% in non-affected individuals¹¹
• Externalizing symptoms
  • Subclinical ADHD showed weaker externalizing symptoms than clinical ADHD, while internalizing symptoms were comparable.¹² However, we also see this as a consequence of an overweighting of externalizing symptoms in the ADHD scales.
  • Subthreshold ADHD showed an increased risk of externalizing disorders and higher scores in eight CBCL scales (somatic complaints, anxiety/depression, social problems, attention problems, delinquent behavior, aggressive behavior, externalizing problems and overall behavior problems) compared to controls¹³
• Social behavior
  • Subclinical ADHD, like clinical ADHD, is more likely to show impairment in recognizing social cues in facial expressions, resulting in impaired social functioning¹⁴
• Education
  • Subclinical ADHD scored as poorly as ADHD on academic (reading and math) and non-academic (school engagement, attendance, peer bullying and parental expectations) outcomes¹⁵
• Comorbidities
  • Subclinical ADHD showed significantly increased comorbidity¹⁶
• Inattention
  • Subclinical ADHD showed increased inattention (4.34) compared to controls (0.33) or from unaffected twins of people with ADHD (0.44), while not reaching the levels of ADHD (7.33)¹⁷
• Hyperactivity/impulsivity
  • Subclinical ADHD showed increased hyperactivity/impulsivity (2.73) compared to controls (0.17) or from unaffected twins of people with ADHD (0.43), not reaching the values of ADHD (5.99) ¹⁷

Lower impairments than in ADHD were found in subclinical ADHD for:

• Executive functions
  • In adults with subclinical ADHD, executive functions were not impaired compared to controls¹⁶

Among very preterm infants, 66.4% showed subclinical ADHD (32.7% subclinical ADHD and 33.6% subclinical ADHD-C). This was 3.32 times the rate of non-preterm infants (20%).¹⁸
Subclinically elevated ADHD symptom scores were also associated with greater executive dysfunction (inhibitory self-control, flexibility, and emergent metacognition).
Subclinically elevated levels of inattentive ADHD were also associated with lower IQ and higher perinatal clinical risk (more days on mechanical ventilation and more days on parenteral nutrition).
Subclinically elevated levels of hyperactive ADHD symptoms were also associated with lower socioeconomic status.