Prevalence, Treatment, and Control of Depressive Symptoms in the United States: Results from the National Health and Nutrition Examination Survey (NHANES), 2005–2008

Discussion

This study demonstrates the significant gap between optimal depression care and population-based, real-world measures of care. Given that such a large segment of the US population (roughly 1 in 5 adults, or 42.1 million Americans) screened positive for at least mild depressive symptoms, it may be seen as a major challenge to our nation's health if such a burdensome disease is so frequently undiagnosed, untreated, or undertreated. In many ways it is analogous to the gap between prevalence of elevated blood pressure in the population and levels of detection, treatment, and "treat-to-target" control of hypertension. Although impressive gains have been made (for example, the proportion of hypertensive patients with at least partially controlled blood pressure, defined by blood pressure <160/95, rose from 16% in 1972 to 67% in 1991);^[18] still, only 34% of patients with hypertension have blood pressure completely under control, 25% are partially treated but uncontrolled, 11% are taking no medication, and 30% are unaware that they even have high blood pressure. Eisenberg and Power^[19] used the phrase "voltage drop" to describe the gap between potentially achievable outcomes and those outcomes actually achieved in real-world practice settings, and ultimately in community-based populations.

Primary care clinicians approach patients not as single disease or risk factors, but as whole persons, understanding that depression confers a direct burden of suffering but also complicates the management of various other chronic diseases or risk factors. For example, the epidemiologic evidence for an association between depression and cardiovascular risk is quite strong.^[20,21] Depression prevalence is also higher among individuals with diabetes,^[22] and depression is correlated with poor glycemic control. Depression and metabolic syndrome are correlated as well, and each is an independent predictor of adverse cardiac outcomes.^[23]

Beyond considering depression as a risk factor, however, depression is also a disabling disease unto itself, accounting for disability, reduced quality of life, loss of work days, damage to relationships, and even suicide.^[24,25] Although recognition of depression has improved, our data show that more than half of US adults with depressive symptoms are untreated, and 3 of 4 people with severe depressive symptoms are not taking antidepressant medications. Treatment to remission significantly reduces relapse rates in depression; however, almost half of people taking antidepressants have not achieved remission of depressive symptoms.^[26]

Formal screening protocols in primary care practices identify many more patients with depressive symptoms than are diagnosed in usual care models. There is an emerging body of evidence to suggest that although screening protocols do detect more cases of depression, they do not by themselves reduce the burden of disease or even improve outcomes.^[27] The US Preventive Services Task Force only recommends screening adults for depression in clinical practices that have systems to ensure accurate diagnosis, effective treatment, and follow-up. However, when coupled with structured approaches to depression care management such as the 3-component model, which integrates nurse care managers and mental health professionals into the primary care practice team, improved outcomes can be achieved. The (Prevention of Suicide in Primary Care Elderly: Collaborative Trial) study showed that medical complexities and comorbid chronic disease common to general internal medicine practices affect treatment outcomes for depression in usual-care settings, but that the impact of comorbidities on depression outcomes can be eliminated with a more intensive approach to depression care.^[28]

There are limitations to our study. The use of a national survey provides generalizable data we can apply to the entire noninstitutionalized US population, but it does lack the clinical specificity that might be obtained from direct review of clinical records. The PHQ-9 is a self-administered instrument validated for screening, diagnosis, and assessment of the severity of depressive symptoms, with a sensitivity and specificity of 88% each for major depression.^[14] It is more easily adapted to high-volume primary care settings than instruments such as the Zung or Hamilton Depression Rating Scales.

Using a PHQ-9 score >5 to indicate mild, moderate, moderately severe, or severe depressive symptoms, NHANES provides a higher prevalence estimate (21.6%, or more than 40 million Americans) than other recent surveys. However, combining only moderate, moderately severe, and severe depressive symptoms gives a point prevalence of 6.8%, which is more consistent with other national estimates of a prevalence over a 12-month period of 6.6%.^[7] This may indicate that other instruments are not detecting mild depressive symptoms, or that the PHQ-9 threshold of 5 may be overly sensitive but not specific.

It is possible that individuals who screened positive on the NHANES PHQ-9 underreported treatment, either because of recall errors or additional factors (eg, stigma associated with mental illness and its treatment). In addition, individuals who report taking an antidepressant drug may be taking it for conditions other than depressive symptoms and therefore have low PHQ-9 scores. This would lead to an overestimate of the proportion of the population treated to remission, which is already low. We also have no repeated measures or longitudinal tracking to assess the impact of treatment on recently diagnosed individuals, or to estimate the rate of partial response to treatment (>50% reduction in PHQ-9 score).

Furthermore, individuals with bipolar depression may have elevated PHQ-9 scores, but may be prescribed mood stabilizers rather than antidepressants for treatment of depressive symptoms. Although this represents an extremely small number of individuals, it could lead to a slight underestimate of antidepressant treatment rates for individuals with moderately severe or severe depressive symptoms.

J Am Board Fam Med. 2011;24(1):33-38. © 2011 American Board of Family Medicine

Cite this: Prevalence, Treatment, and Control of Depressive Symptoms in the United States: Results from the National Health and Nutrition Examination Survey (NHANES), 2005–2008 - Medscape - Jan 01, 2011.