Number needed to harm should be measured for treatments

Communicating Risk: Developing an "Efficiency Index" for Dementia Screening Tests

Diagnostic and screening tests may have risks such as misdiagnosis, as well as the potential benefits of correct diagnosis. Effective communication of this risk to both clinicians and patients can be problematic. The purpose of this study was to develop a metric called the "efficiency index" (EI), defined as the ratio of test accuracy and inaccuracy, to evaluate screening tests for dementia. This measure was compared with a previously described "likelihood to be diagnosed or misdiagnosed" (LDM), also based on "numbers needed" metrics. Datasets from prospective pragmatic test accuracy studies examining four brief cognitive screening instruments (Mini-Mental State Examination; Montreal Cognitive Assessment; Mini-Addenbrooke's Cognitive Examination (MACE); and Free-Cog) were analysed to calculate values for EI and LDM, and to examine their variation with test cut-off for MACE and dementia prevalence. EI values were also calculated using a modification of McGee's heuristic for the simplification of likelihood ratios to estimate percentage change in diagnostic probability. The findings indicate that EI is easier to calculate than LDM and, unlike LDM, may be classified either qualitatively or quantitatively in a manner similar to likelihood ratios. EI shows the utility or inutility of diagnostic and screening tests, illustrating the inevitable trade-off between diagnosis and misdiagnosis. It may be a useful metric to communicate risk in a way that is easily intelligible for both clinicians and patients.

Evaluating cognitive screening instruments with the "likelihood to be diagnosed or misdiagnosed" measure

OBJECTIVES

To calculate "number needed to diagnose" (NND), "number needed to predict" (NNP), and "number needed to misdiagnose" (NNM) for cognitive screening instruments which are commonly used in suspected dementia and mild cognitive impairment, and from these to calculate a "likelihood to be diagnosed or misdiagnosed" (LDM) metric as the ratio of NNM to either NND or NNP.

METHODS

Datasets from pragmatic diagnostic test accuracy studies examining four commonly used cognitive screening instruments (Mini-Mental State Examination, MMSE; Montreal Cognitive Assessment, MoCA; Mini-Addenbrooke's Cognitive Examination, MACE; Six-item Cognitive Impairment Test, 6CIT) were analysed to calculate NND, NNP, and NNM, and from these derive values for LDM.

FINDINGS

Although all the tests had low NND and NNP as desired, NNM was also low. Hence, only MMSE and 6CIT achieved LDM > 1 for dementia diagnosis, and only MACE and 6CIT had LDM > 1 for diagnosis of mild cognitive impairment.

CONCLUSIONS

The likelihood to be diagnosed or misdiagnosed (LDM) metric may indicate the utility or inutility of diagnostic tests for clinicians and patients. LDM values may clarify the inevitable trade-off between sensitivity and specificity and hence clinician purpose in administering the diagnostic test (minimising false negatives or false positives).

Considerations in Applying the Results of Randomized Controlled Clinical Trials to the Care of Older Adults With Kidney Disease in the Clinical Setting: The SHARP Trial

The Study of Heart and Renal Protection (SHARP) found that treatment with ezetemibe and low-dose simvastatin reduced the incidence of major atherosclerotic events in patients with kidney disease. Due to the paucity of evidence-based interventions that lower cardiovascular morbidity in this high-risk population, the SHARP trial will likely have a large impact on clinical practice. However, applying the results of clinical trials conducted in select populations to the care of individual patients in real-world settings can be fraught with difficulty. This is especially true when caring for older adults with complex comorbidity and limited life expectancy. These patients are often excluded from clinical trials, frequently have competing health priorities, and may be less likely to benefit and more likely to be harmed by medications. We discuss key considerations in applying the results of the SHARP trial to the care of older adults with CKD in real-world clinical settings using guiding principles set forth by the American Geriatrics Society's Expert Panel on the Care of Older Adults with Multimorbidity. Using this schema, we emphasize the importance of evaluating trial results in the unique context of each patient's goals, values, priorities, and circumstances.

Interpreting treatment effects from clinical trials in the context of real-world risk information: end-stage renal disease prevention in older adults

IMPORTANCE

Older adults are often excluded from clinical trials. The benefit of preventive interventions tested in younger trial populations may be reduced when applied to older adults in the clinical setting if they are less likely to survive long enough to experience those outcomes targeted by the intervention.

OBJECTIVE

To extrapolate a treatment effect similar to those reported in major randomized clinical trials of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers for prevention of end-stage renal disease (ESRD) to a real-world population of older patients with chronic kidney disease.

DESIGN, SETTING, AND PARTICIPANTS

Simulation study in a retrospective cohort conducted in Department of Veterans Affairs medical centers. We included 371 470 patients 70 years or older with chronic kidney disease.

EXPOSURE

Level of estimated glomerular filtration rate (eGFR) and proteinuria.

MAIN OUTCOMES AND MEASURES

Among members of this cohort, we evaluated the expected effect of a 30% reduction in relative risk on the number needed to treat (NNT) to prevent 1 case of ESRD over a 3-year period. These limits were selected to mimic the treatment effect achieved in major trials of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers for prevention of ESRD. These trials have reported relative risk reductions of 23% to 56% during observation periods of 2.6 to 3.4 years, yielding NNTs to prevent 1 case of ESRD of 9 to 25.

RESULTS

The NNT to prevent 1 case of ESRD among members of this cohort ranged from 16 in patients with the highest baseline risk (eGFR of 15-29 mL/min/1.73 m(2) with a dipstick proteinuria measurement of ≥ 2+) to 2500 for those with the lowest baseline risk (eGFR of 45-59 mL/min/1.73 m(2) with negative or trace proteinuria and eGFR of ≥ 60 mL/min/1.73 m2 with dipstick proteinuria measurement of 1+). Most patients belonged to groups with an NNT of more than 100, even when the exposure time was extended over 10 years and in all sensitivity analyses.

CONCLUSIONS AND RELEVANCE

Differences in baseline risk and life expectancy between trial subjects and real-world populations of older adults with CKD may reduce the marginal benefit to individual patients of interventions to prevent ESRD.