How accurate is the Mini-Cog in detecting dementia among patients in inpatient and outpatient hospital settings?

Why is recognising dementia important?

Dementia is a common and important condition, and many of those living with dementia have never had the condition diagnosed. Diagnosis provides opportunities for social support, advance care planning and, in specific disease types, treatment with medication. However, incorrectly diagnosing dementia when it is not present (a false-positive result) can be distressing for the individual and their family and lead to a waste of resources in diagnostic tests.

What was the aim of the review?

The aim of this Cochrane Review was to find out how accurate the Mini-Cog test is for detecting dementia among patients in inpatient and outpatient hospital settings. The researchers included three studies to answer this question.

What was studied in the review?

The Mini-Cog is a short test of memory and thinking skills that tests the ability of an individual to remember three specific objects, named at the beginning of a short assessment, repeated at the time and recalled by the individual later. In addition, the individual being assessed is asked to draw a clock face at a specific time. Points are scored based on the ability to recall the three items and the completeness of the clock. The Mini-Cog is a short test that would typically be used to identify if someone was having difficulty with memory and thinking skills who would benefit from referral to a specialist for more detailed assessment.

What are the main results of the review?

The review included data from three relevant studies with a total of 2560 participants. However, the study authors did not use data from many of those participants they assessed, leaving results from only 1415 participants that provide complete and useful information for addressing the review question.

All three studies scored the Mini-Cog results in the way that was recommended by the developers of the tool. There was no clear pattern in the results of what a positive result of a Mini-Cog test meant across the three studies, making it difficult to draw summary conclusions. Using the studies with the highest and lowest Mini-Cog results indicated that if the Mini-Cog were to be used in secondary care in a group of 1000 people, where 640 (64%) have dementia, an estimated 510 to 557 would have a positive Mini-Cog, of which 0 to 126 would be incorrectly classified as having dementia. Of the 443 to 490 people with a result indicating dementia is not present, 83 to 256 would be incorrectly classified as not having dementia.

How reliable are the results of the studies in the review?

In the included studies, the diagnosis of dementia was made by assessing all patients with a detailed clinical assessment. Detailed clinical assessment is the reference standard to which the Mini-Cog was compared. This is likely to have been a reliable method for determining whether patients actually had dementia. However, there were some problems with how the studies were conducted in terms of the people who were included and how the Mini-Cog was calculated, which could result in the Mini-Cog appearing more accurate than it actually is. We decided that it was not appropriate to group the studies together to describe the average performance of the Mini-Cog, due to the differences among them.

To whom do the results of this review apply?

The studies included in the review were conducted in the USA, Germany, and Brazil. Two studies included those patients referred to specialists evaluating memory and thinking skills, and one study recruited individuals attending a medical outpatient clinic. The percentage of people with a final diagnosis of dementia was between 32% and 87% (an average of 64%).

What are the implications of this review?

The small number of studies identified and variation in how they used the Mini-Cog limit the evidence to make recommendations, and suggest that Mini-Cog may not be the best test to recommend for use in inpatient and outpatient secondary care hospital settings.

How up-to-date is this review?

The review authors searched for and considered studies published up to March 2019.

Authors' conclusions: 

This review identified only a limited number of diagnostic test accuracy studies using Mini-Cog in secondary care settings. Those identified were at high risk of bias related to patient selection and high concerns related to index test conduct and applicability. The evidence was indirect, as all studies evaluated Mini-Cog differently from the review question, where it was anticipated that studies would conduct Mini-Cog and independently but contemporaneously perform a reference standard assessment to diagnose dementia. The pattern of test accuracy varied across the three studies. Future research should evaluate Mini-Cog as a test in itself, rather than derived from other neuropsychological assessments. There is also a need for evaluation of the feasibility of the Mini-Cog for the diagnosis of dementia to help adequately determine its role in the clinical pathway.

Read the full abstract...
Background: 

The diagnosis of Alzheimer's disease dementia and other dementias relies on clinical assessment. There is a high prevalence of cognitive disorders, including undiagnosed dementia in secondary care settings. Short cognitive tests can be helpful in identifying those who require further specialist diagnostic assessment; however, there is a lack of consensus around the optimal tools to use in clinical practice. The Mini-Cog is a short cognitive test comprising three-item recall and a clock-drawing test that is used in secondary care settings.

Objectives: 

The primary objective was to determine the diagnostic accuracy of the Mini-Cog for detecting Alzheimer's disease dementia and other dementias in a secondary care setting. The secondary objectives were to investigate the heterogeneity of test accuracy in the included studies and potential sources of heterogeneity. These potential sources of heterogeneity will include the baseline prevalence of dementia in study samples, thresholds used to determine positive test results, the type of dementia (Alzheimer's disease dementia or all causes of dementia), and aspects of study design related to study quality.

Search strategy: 

We searched the following sources in September 2012, with an update to 12 March 2019: Cochrane Dementia Group Register of Diagnostic Test Accuracy Studies, MEDLINE (OvidSP), Embase (OvidSP), BIOSIS Previews (Web of Knowledge), Science Citation Index (ISI Web of Knowledge), PsycINFO (OvidSP), and LILACS (BIREME). We made no exclusions with regard to language of Mini-Cog administration or language of publication, using translation services where necessary.

Selection criteria: 

We included cross-sectional studies and excluded case-control designs, due to the risk of bias. We selected those studies that included the Mini-Cog as an index test to diagnose dementia where dementia diagnosis was confirmed with reference standard clinical assessment using standardised dementia diagnostic criteria. We only included studies in secondary care settings (including inpatient and outpatient hospital participants).

Data collection and analysis: 

We screened all titles and abstracts generated by the electronic database searches. Two review authors independently checked full papers for eligibility and extracted data. We determined quality assessment (risk of bias and applicability) using the QUADAS‐2 tool. We extracted data into two‐by‐two tables to allow calculation of accuracy metrics for individual studies, reporting the sensitivity, specificity, and 95% confidence intervals of these measures, summarising them graphically using forest plots.

Main results: 

Three studies with a total of 2560 participants fulfilled the inclusion criteria, set in neuropsychology outpatient referrals, outpatients attending a general medicine clinic, and referrals to a memory clinic. Only n = 1415 (55.3%) of participants were included in the analysis to inform evaluation of Mini-Cog test accuracy, due to the selective use of available data by study authors. There were concerns related to high risk of bias with respect to patient selection, and unclear risk of bias and high concerns related to index test conduct and applicability. In all studies, the Mini-Cog was retrospectively derived from historic data sets. No studies included acute general hospital inpatients. The prevalence of dementia ranged from 32.2% to 87.3%. The sensitivities of the Mini-Cog in the individual studies were reported as 0.67 (95% confidence interval (CI) 0.63 to 0.71), 0.60 (95% CI 0.48 to 0.72), and 0.87 (95% CI 0.83 to 0.90). The specificity of the Mini-Cog for each individual study was 0.87 (95% CI 0.81 to 0.92), 0.65 (95% CI 0.57 to 0.73), and 1.00 (95% CI 0.94 to 1.00). We did not perform meta-analysis due to concerns related to risk of bias and heterogeneity.

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