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#187 CBC (Confusing Broad Check) for Screening?

What is the evidence for screening with a CBC (Complete Blood Count) in asymptomatic, non-pregnant adults?

CBC or its components should NOT be ordered for screening asymptomatic non-pregnant adults as it does not reduce mortality. When CBC is tested routinely without cause, up to 11% are abnormal but <1% require management change. It is unclear which patients benefit and serious disease is virtually never found.  

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  • Systematic review of 16 Randomized Controlled Trials (RCTs) of periodic health checks (screening):1  
    • Four included CBC components with other screening tests and reported no cancer-specific or overall mortality reduction.   
  • CBC components in population screening, case-finding (looking for illness in higher risk people), hospital admission screening, and pre-op screening.   
    • Population screening: 
      • 1,080 non-pregnant women age 20-64, 11% anemic (hemoglobin <120g/L) but none had colon cancer.2 
    • Case-finding: 11 observational studies.  
      • Seven from 1987 review,3 evidence does not show benefit in identifying mild asymptomatic abnormalities. Example 
        • From 799 ambulatory patients 475 leukocyte tests, 11% abnormal but no asymptomatic disease identified.4   
      • Four other studies:  
        • 595 patients (1,540 CBC components ordered): 6.4% were abnormal, 1.2% investigated, 0.2% led to management change.5   
        • Others similar.6-8   
    • Pre-Op screening: From four observational studies (214-1,005 patients)9 management was changed 0%, 0%, 0.2% and 2%.   
    • Admission screening: Two observational studies (301-302 patients), ~11% had abnormal CBC components and ≤0.6% led to management changes.10,11   
  • Stating “management changed does not mean patients benefited.  
  • Harms of excess investigation not described.  
  • Screening means testing healthy individuals for asymptomatic disease that could respond to early intervention to prevent suffering or mortality. 
  • When diseases are uncommon (~1%): Only ~16% of abnormals are real disease.12 
    • ~80% of abnormal leukocyte screenings were physiological or test variance.2   
    • 60% of abnormal CBC components normalized by 18 months.5  
  • Serious diseases like colon cancer have better screening tests (FIT testing).     
  • CDC, US Preventive Task Force, and Choosing Wisely do not recommend screening with CBC.13-15  
    • Only pregnancy screening consistently advised.13,14 
  • About 70% of primary care clinicians would order a screening CBC in a 55 year old woman16,17 and ordering CBC predicts other excess screening.16   

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  • G. Michael Allan MD CCFP
  • Jennifer Young MD CCFP-EM

1. Krogsbøll LT, Jørgensen KJ, Grønhøj Larsen C, et al. Cochrane Database Syst Rev. 2012; 10:CD009009.

2. Elwood PC, Waters WE, Greene WJ, et al. BMJ. 1967; 4:714-17.

3. Shapiro MF, Greenfield S. Ann Intern Med. 1987; 106:65-74.

4. Rich EC, Crowson TW, Connelly DP. JAMA. 1983: 249:633-6.

5. Rüttimann S, Clémençon D, Dubach UC. Ann Intern Med. 1992; 116(1):44-50.

6. Boland BJ, Wollan PC, Silverstein MD. Am J Med. 1996; 101(2):142-52.

7. Boland BJ, Wollan PC, Silverstein MD. Am J Med Sci. 1995; 309(4):194-200.

8. Domoto K, Ben R, Wei JY, et al. Am J Public Health. 1985; 75(3):243-5.

9. Czoski-Murray C, Lloyd Jones M, McCabe C, et al. Health Technol Assess. 2012; 16(50).

10. Frye EB, Hubbell FA, Akin BV, et al. J Gen Intern Med. 1987; 2(6):373-6.

11. Mozes B, Haimi-Cohen Y, Halkin H. Postgrad Med J. 1989; 65(766):525-7.

12. Wians FH. Lab Med. 2009; 40(2):105-13.

13. Centre for Disease Control and Prevention. Screening for Anemia 1998. Available at: Last accessed: March 14, 2017.

14. US Preventive Services Task Force. Available at: Last accessed: March 14, 2017.

15. Choose Wisely Canada – Family Medicine. Available at: Last accessed: March 17, 2017.

16. Fung D, Schabort I, MacLean CA, et al. Can Fam Physician. 2015; 61(3):256-62.

17. Chacko KM, Feinberg LE. Am J Prev Med. 2007; 32(1):59-62.

Authors do not have any conflicts of interest to declare.

Les auteurs n’ont aucun conflit d’intérêts à déclarer.