NURS 832 Week 3 Discussion Board Forum 1 on Screening Test Accuracy Example

Discussion Board Forum 1: What a Positive Screen Really Means

NURS 832 Clinical Prevention and Biostatistics, Discussion Board Forum 1

Thread by [Student Name]

The clinic and the classmate replied to are composites written for a model discussion; the studies cited are real, and the predictive values are the student's own calculations from the published sensitivity and specificity.

"Does this mean I'm depressed?" A patient asked me that last week after scoring 3 on the PHQ-2 at a routine visit in our rural family practice. The honest answer is "probably not, but we need to find out," and the reason lies in the difference between how a test performs and what its result means.

Sensitivity tells us what fraction of truly ill people the test catches; specificity is the proportion without the disease who test negative. Both describe the test. Positive predictive value, the proportion of positive results that are true, and negative predictive value describe what a result means for the person in front of us, and they depend on prevalence (Macha & McDonough, 2012).

The PHQ-2 is well studied. Levis and colleagues pooled raw data from 100 studies covering 44,318 people; in that synthesis, 10% of whom had major depression, a PHQ-2 cutoff of 3 or greater had a sensitivity of 0.72 and a specificity of 0.85 against semistructured interviews, while a cutoff of 2 or greater had a sensitivity of 0.91 and a specificity of 0.67 (Levis et al., 2020). Using those figures for 1,000 patients, I calculated:

At 10% prevalence, about 65% of positive screens at a cutoff of 3 are false positives, and at 5% about 80% are. Yet a negative screen is very reassuring. The choice of cutoff is a trade-off: lowering it to 2 catches more true cases, 91 instead of 72 per 1,000 at 10% prevalence, but more than doubles the false positives. In a busy rural clinic with one behavioral health consultant, that trade-off is not only statistical. Every false positive costs a PHQ-9, several minutes of interview and sometimes a referral, and every missed case is a person whose depression goes untreated. Knowing the numbers lets a clinic choose its cutoff deliberately rather than by habit. A screening test can be good at finding disease and still be wrong about most of the people it flags.

Does that make screening a mistake? Not when screening has two steps. The task force's 2023 statement gives adult depression screening a B grade, judging with moderate certainty that the net benefit is moderate (Barry et al., 2023), and in practice a positive PHQ-2 leads to the PHQ-9 and a clinical interview rather than a diagnosis. In our clinic, that means a positive PHQ-2 triggers the PHQ-9 at the same visit, and I explain to patients that the first screen only tells us to ask more questions.

Reply to Hannah

Hannah, your post on mammography connects well to the PHQ-2 problem, because repeated screening multiplies false positives over time. In a study of 903,495 women screened at 126 facilities in the Breast Cancer Surveillance Consortium, the ten-year cumulative probability of at least one false-positive recall with annual screening was 49.6% with tomosynthesis and 56.3% with digital mammography, and it was substantially lower with biennial screening, 35.7% to 38.1% (Ho et al., 2022). In other words, about half of women screened every year for a decade can expect at least one recall that turns out not to be cancer. That does not argue against screening, but it does argue for telling patients in advance that a callback is common and usually benign, and for discussing screening interval as a way to reduce false positives. How do you prepare your patients for a callback?

References

Barry, M. J., Nicholson, W. K., Silverstein, M., Chelmow, D., Coker, T. R., Davidson, K. W., Davis, E. M., Donahue, K. E., Jaén, C. R., Li, L., Ogedegbe, G., Pbert, L., Rao, G., Ruiz, J. M., Stevermer, J. J., Tsevat, J., Underwood, S. M., & Wong, J. B. (2023). Screening for depression and suicide risk in adults: US Preventive Services Task Force recommendation statement. JAMA, 329(23), 2057-2067. https://doi.org/10.1001/jama.2023.9297

Ho, T. H., Bissell, M. C. S., Kerlikowske, K., Hubbard, R. A., Sprague, B. L., Lee, C. I., Tice, J. A., Tosteson, A. N. A., & Miglioretti, D. L. (2022). Cumulative probability of false-positive results after 10 years of screening with digital breast tomosynthesis vs digital mammography. JAMA Network Open, 5(3), Article e222440. https://doi.org/10.1001/jamanetworkopen.2022.2440

Levis, B., Sun, Y., He, C., Wu, Y., Krishnan, A., Bhandari, P. M., Neupane, D., Imran, M., Brehaut, E., Negeri, Z., Fischer, F. H., Benedetti, A., & Thombs, B. D. (2020). Accuracy of the PHQ-2 alone and in combination with the PHQ-9 for screening to detect major depression: Systematic review and meta-analysis. JAMA, 323(22), 2290-2300. https://doi.org/10.1001/jama.2020.6504

Macha, K., & McDonough, J. P. (2012). Epidemiology for advanced nursing practice. Jones & Bartlett Learning.