In epidemiology and mass screening, overdiagnosis, or over diagnosis, is the diagnosis of non-harmful disease by diagnostic tests. Overdiagnosis inflates the importance of the screening problem. Overdiagnosis is also an issue in trauma and emergency medicine.
An informal but memorable term is VOMIT, or Victim Of Modern Imaging Technology. In emergency medicine, the use of imaging to rule out clinically unlikely syndromes, sometimes as part of defensive medicine, may lead to extensive, expensive, and even hazardous interventions over an equivocal finding on imaging. Imaging has an enormous value, but is sometimes is not used appropriately. Examples include ankle X-rays without first establishing the Ottawa ankle rules to determine that a fracture probably exists,  or the use of d-dimer levels for ruling out deep venous thrombosis without going immediately to more expensive doppler ultrasonography.
Prevalence of overdiagnosis
Overdiagnosis has been shown to occur in:
- Breast cancer (rate may 10% or higher)
- Lung cancer (rate may be 2%)
- Prostate cancer (rate may be 15% in whites and 37% in blacks)
- Renal cancer.
- Thyroid cancer.
Overdiagnosis can be detected by studying the screening program with a randomized controlled trial in which one arm of the trial the subjects are randomly assigned to the screening program and in the other arm of the trial, subjects are assigned to the control group. Examination of the rate of diagnosis over time detects overdiagnosis: 
- "If overdiagnosis has not occurred, the cumulative number of cases in each arm will equalize with time after screening stops (i.e., catch-up) as the counterparts of the earlier screen-detected cancers are detected symptomatically in the control arm."
- "If overdiagnosis has occurred, the number of cases in both arms will never equalize because the excess cases in the intervention arm will have no counterparts in the control arm."
Solutions to overdiagnosis
Removing "cancer" from names of low-risk diagnoses
It has been proposed that some pre-malignant conditions have the words cancer or carcinoma removed from their name. Another proposal is to name conditions "IDLE (indolent lesions of epithelial origin)".
- Black WC, Welch HG (April 1993). "Advances in diagnostic imaging and overestimations of disease prevalence and the benefits of therapy". N. Engl. J. Med. 328 (17): 1237–43. PMID 8464435.
- Esserman L, Shieh Y, Thompson I (2009). "Rethinking screening for breast cancer and prostate cancer.". JAMA 302 (15): 1685-92. DOI:10.1001/jama.2009.1498. PMID 19843904. Research Blogging.
- Bachmann LM et al. (22 February 2003), "Accuracy of Ottawa ankle rules to exclude fractures of the ankle and mid-foot: systematic review", BMJ 326: 417, DOI:10.1136/bmj.326.7386.417
- Wiener RS, Schwartz LM, Woloshin S (2011). "Time trends in pulmonary embolism in the United States: evidence of overdiagnosis.". Arch Intern Med 171 (9): 831-7. DOI:10.1001/archinternmed.2011.178. PMID 21555660. Research Blogging.
- Zackrisson S, Andersson I, Janzon L, Manjer J, Garne JP (March 2006). "Rate of over-diagnosis of breast cancer 15 years after end of Malmö mammographic screening trial: follow-up study". BMJ 332 (7543): 689–92. DOI:10.1136/bmj.38764.572569.7C. PMID 16517548. PMC 1410836. Research Blogging.
- Jørgensen KJ, Gøtzsche PC (2009). "Overdiagnosis in publicly organised mammography screening programmes: systematic review of incidence trends.". BMJ 339: b2587. DOI:10.1136/bmj.b2587. PMID 19589821. Research Blogging.
- Kalager M, Adami HO, Bretthauer M, Tamimi RM (2012). "Overdiagnosis of invasive breast cancer due to mammography screening: results from the norwegian screening program.". Ann Intern Med 156 (7): 491-9. DOI:10.1059/0003-4819-156-7-201204030-00005. PMID 22473436. Research Blogging.
- Marcus PM, Bergstralh EJ, Zweig MH, Harris A, Offord KP, Fontana RS (June 2006). "Extended lung cancer incidence follow-up in the Mayo Lung Project and overdiagnosis". J. Natl. Cancer Inst. 98 (11): 748–56. DOI:10.1093/jnci/djj207. PMID 16757699. Research Blogging.
- Etzioni R, Penson DF, Legler JM, et al (July 2002). "Overdiagnosis due to prostate-specific antigen screening: lessons from U.S. prostate cancer incidence trends". J. Natl. Cancer Inst. 94 (13): 981–90. PMID 12096083.
- Welch HG and Albertsen PC. Prostate cancer diagnosis and treatment after the introduction of prostate-specific antigen screening: 1986–2005. J Natl Cancer Inst 2009 Aug 31; [e-pub ahead of print]. DOI:10.1093/jnci/djp278
- Lane BR, Abouassaly R, Gao T, Weight CJ, Hernandez AV, Larson BT et al. (2010). "Active treatment of localized renal tumors may not impact overall survival in patients aged 75 years or older.". Cancer 116 (13): 3119-26. DOI:10.1002/cncr.25184. PMID 20564627. Research Blogging.
- Brito, J. P.; J. C. Morris, V. M. Montori (2013-08-27). "Thyroid cancer: zealous imaging has increased detection and treatment of low risk tumours". BMJ 347 (aug27 4): f4706-f4706. DOI:10.1136/bmj.f4706. ISSN 1756-1833. Retrieved on 2013-08-28. Research Blogging.
- Esserman LJ, Thompson IM, Reid B (2013). "Overdiagnosis and Overtreatment in Cancer: An Opportunity for Improvement.". JAMA. DOI:10.1001/jama.2013.108415. PMID 23896967. Research Blogging.