What’s the difference between acute and chronic illness?
Doctors often categorise medical conditions as ‘acute’ and ‘chronic’. They also use phrases like ‘subacute’ and ‘recurrent’. But what do these terms mean? There is no agreed definition of any of them, but the following is often stated.
Acute
Definition – Less than 4 weeks, with resolution of the problem
E.g. a patient with crushing chest pain and an abnormal ECG is experiencing an acute emergency. In this context, acute means ‘short-term’. In this case, it means that within minutes, the patient need a specific series of drugs and a team of medical professionals – to deal with the heart (or severe angina) attack.
But not all acute problems are severe: another one, a nose bleed, gets better with no treatment.
Chronic
Definition – Over 12 weeks
E.g. another patient may feel his chest tighten when he walks up stairs, but the discomfort fades when he rests, and it’s been this way for years. This is ‘chronic angina’. In this context, chronic means long-term.
It can be serious and need medical attention, but can usually be managed with medication – and not necessarily today. This month is fine. In other cases, like mild psoriasis, a chronic condition may need no treatment.
Note. Actually there is no agreed definition of ‘chronic’. For example, the CDC in the USA defines it as over 1 year.
Subacute
Definition – 4-12 weeks, with resolution (sometimes partial) of the problem
A ‘subacute condition’ is somewhere in between. For example, last month, a woman could climb three flights; last week, only two; and this week one, only one. This is mild heart failure. Subacute illnesses like this, may be hazardous in their own way and need attention – ideally this week. They can be improved if treated appropriately. But they may be difficult to diagnose. And, if you ignore or mismanage them, they can spiral out of control.
Recurrent
Definition – 4 or more episodes a year, with resolution in between
E.g. a 32 year old woman with 4 UTIs a year. She is well between episodes. Nonetheless it is still a debilitating problem.
Example
Chronic Kidney Disease (CKD) and Acute Kidney Injury (AKI) mean long and short term. The former usually comes on over months and years, the latter over hours or days.
Summary
We have described what’s the difference between acute and chronic illness. And described a subacute and recurrent one. These 4 phrases indicate the duration and pattern of the illness. They do not indicate severity, but they do tell you the speed that treatment is needed (if required).
Last Reviewed on 13 March 2024