Overview of online symptom checkers: the basics things you need to know

This is my first article on online symptom checkers and it contains basic information about how they work and what basic limitations they have. This article will be followed by several other articles on this topic and we will go into much more depth about how you can use them and what alternatives you have.

Online symptom checkers are very common these days and provide quick and useful way to analyze your medical symptoms. They may also suggest treatment options and need for further diagnostic testing. Online symptom checkers from reputable websites such as WebMd analyze your symptoms very accurately and they have very refined and extensive database to help you get accurate results.

Online symptom checkers basically use computerized algorithm to arrive at the list of possible diagnoses. Any computer based decision support algorithm needs some basic data to function. When you are sick, there are some basic information about your symptoms that are needed to analyze your symptoms. Most online symptom checkers from reputable health websites ask you basic questions designed to get the following data about your symptoms:

Data collection:

  1. Demographic: Age/sex
  2. Chief symptom: main problem such as pain or dizziness or vomiting
  3. Onset: Gradual or abrupt
  4. location: Where exactly is your symptom located
  5. Intensity: How bad is your symptom
  6. Exacerbating factors: What makes it worse
  7. Ameliorating factors: What makes it better
  8. Associated symptoms: What other symptoms you have besides your chief symptom

Any online symptom checker that asks you about these basic eight things has the ability to collect necessary basic pieces of information to analyze your symptoms. Any doctor you see for a new symptom is also required to ask and make note of these eight basic facts about your symptoms. However, there are limitations to what computers can do while gathering the data:



  1. Computers define symptoms by a list of words: You can only use a limited list of words to pick and choose your symptoms when you use online symptom checkers. When you see a real doctor, you are asked to describe your symptoms in your own words. How you feel when you are sick can be hard to describe by picking a word from a list. A good doctor who listens to your compliant carefully can relate your unique symptoms to your internal organs and make educated guess about what could be wrong with your body. Online symptom checkers can only give you a few adjectives to describe your symptom and you are forced to choose one from the list. This is why an online symptom checker gives you a long list of possible diagnoses while your doctor narrows down your symptom to just a few possible conditions and orders some additional tests to figure out the correct diagnosis.
  2. You are only defined by your age and gender: A good doctor needs to know who you are as a person before he/she can put your unique symptoms in the right context. An online symptom checker only uses your age and your gender to analyze your symptoms. It does not use your personal medical history, your occupation, your lifestyle, your pain tolerance, your exercise tolerance and other personal information that can play a critical role when a real doctor analyses your symptoms.
  3. Stop and seek medical attention prompt: Most online symptom checkers have a built in function that tells you to stop using the online symptom checker and seek prompt medical attention (we will call this “STOP prompt” for our discussion). This option is triggered when you pick a symptom that is associated with possible life threatening emergency. This a very good thing and you need to follow this advice when it prompts you to do so. However, you need to be aware that you may still have a life threatening emergency and not get STOP. For example, when you use online symptom checker to analyze your chest pain, it will trigger STOP prompt if you put in certain specific adjectives to describe your chest pain. When you don’t use those specific adjectives, it may give you 20 possible conditions that may have caused your chest pain. Among those 20 conditions, it will include life threatening conditions such as heart attacks or blood clots. Just because you did not use one of the common adjectives used in typical pain associated with heart attack does not mean that you do not have a heart attack. You need to be aware of this when using any online symptom checker. Do not feel reassured about your symptom if you do not get the STOP prompt.
  4. Too many possible diagnosis: Like we discussed earlier, online symptom checkers use data that is less specific to you. To compensate for the less specific data, online symptom checkers use very broad and inclusive algorithm when they analyze those data. As a result, the number of possible diagnosis you get can be a large number. It can be overwhelming to look through them and decide what to do next.
  5. Does not consider the sequence of symptoms: In real medical practice, the exact sequence of events and how they progresses can help a doctor very much to narrow down the possible diagnosis. For example, if you became dizzy first and then passed out, it will have very different implications that if you had passed out first and were dizzy when you woke up. However, an online symptom checker can only give you those diagnoses that have both dizziness and passing out as listed symptoms.
  6. Does not define gradual vs sudden: Most online symptom checker have questions that ask you about the rapidity of symptoms. However, those are not clearly defined for the particular symptom. For some slowly developing disease, symptom progression in 1 week can be very rapid. In other cases, the same symptom may have different diagnoses based on whether it happened within a few minutes, a few seconds or even within a fraction of a second.


With this basic knowledge about online symptom analyzers, you will be able to learn more about them and use them to your advantage. On the next article I will tell you how to get the maximum benefit from online symptom analyzers. Please check your twitter feed to get notification when the next article is done. If you have not subscribed to my twitter feed, here is my twitter handle: