How the Clock-Drawing Test Screens for Dementia

The clock-drawing test (CDT) is a simple tool used to check for signs of dementia, including Alzheimer’s disease. It is often used in combination with other screening tests but can provide valuable clues on its own.

The CDT measures several cognitive abilities at once, including attention, hearing comprehension, visual memory, and motor skills. To complete the clock-drawing test, one must draw a clock with hands pointing to a specific time. While the CDT can be done quickly with a pencil and paper, it cannot be used to specify the exact type of dementia one has.

This article explores the aims of the clock-drawing test, how it is done, and what the scores mean. It also discusses some of the benefits and drawbacks of testing.

Aims of the Clock-Drawing Test

The aim of the clock-drawing test is to see if there is any loss of a person's cognition. In simple terms, cognition is the ability to learn, understand, and reason through experience, thoughts, and senses.

The clock-drawing test is able to detect mental decline, as people with dementia often have problems reading traditional clocks. Reading clocks requires you to interpret the placement of the hands on a clock and the time they are meant to represent. This ability is often lost in people with early dementia.

With dementia, many aspects of cognition are affected, including:

• Executive function: Mental skills involving working memory, flexible thinking, and self-control
• Visual-spatial ability: The ability to perceive the relationship of objects in space
• Motor programming: The ability to represent sequence and movement in abstract form
• Attention and concentration

All of these skills are involved when a person is asked to draw a clock. Any difficulties with the task suggest that a person may have dementia.

Studies suggest that the clock-drawing test can detect early dementia even when other tests, such as mini-mental state exam (MMSE), are normal.

How the Clock-Drawing Test Is Done

The clock-drawing test can be given by a doctor or other qualified professional. It only requires a pencil and a piece of paper with a pre-drawn circle on it.

The doctor will first ask the person to draw the numbers on the face of the clock. Next, the person will be asked to draw the hands to show a specific time. Different times can be used, but many doctors choose 10 minutes after 11 as a standard value.

One variation of the test is to provide the person with a blank piece of paper and ask them to draw a clock showing 10 minutes after 11. The word "hands" is not used to avoid giving clues. A total of three drawings are typically used with each drawing done within a specific time limit.

Clock-Drawing Test Scoring

There are as many as 15 different ways to score the clock-drawing test. Some methods are complex and will award as many as 10, 15, or 20 points based on whether or not the sequence of numbers, the placement of numbers, and the placement of the hands are correct.

Errors such as missing numbers, missing hands, repeated numbers, the wrong sequence of numbers, or the incorrect time can also factor into the interpretation. Even the refusal to draw a clock may be interpreted as a sign of dementia.

This simplest scoring method allots one point if the drawing is correct and zero points if it is not. A 2012 study in the Danish Medical Journal concluded that the simplest method is just as accurate in diagnosing early dementia as complex methods.

For its part, the Alzheimer's Association endorses the simple method of scoring.

Benefits and Limitations

The early detection of dementia is important as there are medications that may help slow the progression of Alzheimer's disease. To this end, the clock-drawing test offers benefits in that:

• It is quick and simple. The test can be completed in a few minutes and only requires a pencil and paper.
• It is easy to administer. The test doesn't require much training if a simple scoring method is used.
• It can screen for delirium. Delirium, a sudden deterioration of cognition, can also be detected with the test. Causes may include a severe illness, brain infection, or drug reaction rather than mental decline.

At the same time, the clock-drawing test has its drawbacks. Among the limitations:

• It cannot diagnose the type of dementia. The test can be a strong indication of early dementia, but it cannot tell if Alzheimer's or some other condition is involved. Other tests would be needed.
• It can be misinterpreted. If the tester is not a trained medical professional, they can mistake conditions like vascular dementia for Alzheimer's and not pursue the appropriate diagnosis.

Summary

The clock-drawing test is a quick way to screen for early dementia, including Alzheimer's disease. It involves drawing a clock on a piece of paper with numbers, clock hands, and a specific time. The inability to do so is a strong indication of mental decline.

Even so, the clock-drawing test cannot tell which type of dementia is involved or if the loss of cognition is due to some other condition like a severe illness, brain infection, or drug reaction.