Clinical & Subclinical Diseases: Definition & Examples

Instructor: Megan Gilbert

Megan has a master's degree in nursing and is a board certified Women's Health Nurse Practitioner. Her area of clinical focus is the impact of infectious disease on pregnancy. She has experience teaching college allied health classes. She is also a certified EMT and holds a certificate of added qualification in electronic fetal monitoring.

This lesson begins with an explanation of clinical and subclinical disease by using an example of hypothyroidism in two sisters. It then explains two further examples of clinical and subclinical disease.

Mom's Yearly Check-up

You receive a call from your mother, and she sounds upset. She's just been to the doctor for her yearly physical and has been diagnosed with subclinical hypothyroidism, but she doesn't believe it. She feels great! Never better! How could she have a failing thyroid? She thought hypothyroidism caused people to gain a lot of weight, have constipation, feel really cold, and lose their hair. When her sister was first diagnosed with hypothyroidism she was always freezing, she gained weight (and bought new clothing), and had no energy.

You begin to explain to your mother the difference between clinical disease and subclinical disease. Her sister, who was symptomatic, is an example of someone who experienced clinical disease. Your mother, who is experiencing the early stages of the condition and is not yet having any symptoms, is experiencing subclinical disease.

Subclinical Disease

Your mother is experiencing subclinical disease, or having a condition but not yet having any symptoms from the condition. Occasionally, individuals may experience mild symptoms, may report non-specific symptoms (for example, a patient may report being more tired, but not report true fatigue), or may report that they have been feeling 'different' lately, but they are unable to be more specific.

Generally, the disease is in its most mild and earliest stages. Often, it has not progressed to the point of causing any symptoms, and it may be impossible for providers to diagnose. However, it may be discovered during routine laboratory screenings. Screening programs are designed to identify conditions early in their disease course when they are easier to treat and before they have caused substantial damage to the body.

Clinical Disease

Clinical disease is what your aunt was experiencing. It is having the full disease condition, often with a variety of symptoms, after the disease has progressed past the initial stages. At this stage it will cause signs and symptoms that may provide clues as to the cause of the condition.

The diagnosis will generally need to be confirmed with radiologic imaging or laboratory testing. For example, if you suspect hypothyroidism because your aunt complains of being tired, constipated, gaining weight, and experiencing hair loss, her doctor will need to do blood work to confirm this diagnosis.


Subclinical and clinical disease states occur for a variety of conditions, but two specific examples are chlamydia and diabetes. Screening programs can diagnose conditions in the earliest stages and initiate treatment before they become more severe or damage the body.


Infections can be subclinical or clinical. For example, if a young man goes to a Sexually Transmitted Infections clinic because he is experiencing pain when he urinates, and is diagnosed with chlamydia (a very common sexually transmitted infection), he would have a clinical infection. On the other hand, an example of a subclinical infection would be a young woman who has no complaints or symptoms but goes to her doctor for a routine well woman annual visit. There, she tests positive for chlamydia as part of her recommended screening. This is subclinical because she wasn't exhibiting any signs of the infection yet.

Many infections show this same pattern: the infection is present within the body and the patient is capable of infecting others, but the individual is not yet displaying any outward symptoms.


Diabetes is another condition that can exist in a subclinical state. It is a condition when the pancreas fails to properly release insulin. This lack of insulin prevents sugar from entering cells normally, which in turn causes the cells to become energy-starved while the blood sugar level continues to rise (because the sugar is trapped outside of the cells in the blood).

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