CBC Frequency for Older Adults in Skilled Nursing Facilities
CBC testing should only be performed for SNF residents when there is clinical suspicion of infection, within 12-24 hours of symptom onset (or sooner if the resident is seriously ill), and not as a routine screening test. 1
Indications for CBC Testing in SNF Residents
- CBC with differential should be performed when infection is suspected based on clinical presentation, not as a routine screening test 1
- Testing should be completed within 12-24 hours of symptom onset, or sooner if the resident is seriously ill 1
- The manual differential is preferred to assess bands and other immature forms of white blood cells 1
Clinical Significance of CBC Results
- An elevated WBC count (≥14,000 cells/mm³) warrants careful assessment for bacterial infection, with or without fever 1
- Left shift (percentage of band neutrophils or metamyelocytes ≥16%; or total band neutrophil count ≥1,500 cells/mm³) is a significant indicator of potential bacterial infection 1
- Leukocytosis with a WBC count >14,000 cells/mm³ has a likelihood ratio of 3.7 for detecting bacterial infection 1, 2
When Additional Testing May Not Be Indicated
- In the absence of fever, leukocytosis, left shift, or specific clinical manifestations of a focal infection, additional diagnostic tests may not be indicated due to low potential yield 1
- Non-bacterial infections, however, cannot be excluded based solely on normal CBC results 1
Important Considerations for CBC Testing
- Advance directives should be reviewed prior to any intervention, including laboratory testing 1
- If specific diagnostic measures are consciously withheld, the reasons should be documented in the medical record 1
- Tests should only be performed if they have reasonable diagnostic yield, are low risk, reasonable in cost, and will improve patient management 1
Pitfalls to Avoid
- Avoid routine or scheduled CBC testing in asymptomatic residents, as this leads to unnecessary costs and potential false positives 1
- Do not rely solely on CBC results to rule out infection, as typical symptoms and signs of infection are frequently absent in older adults 1
- Remember that basal body temperature decreases with age and frailty, making classic definitions of fever less reliable in this population 1
- Avoid ordering CBCs when results will not change management decisions 1
Special Situations
- For suspected UTI: CBC with urinalysis and urine culture should be performed only for residents with acute onset of UTI-associated symptoms (fever, dysuria, gross hematuria, new/worsening incontinence) 1
- For suspected pneumonia: CBC with pulse oximetry and possibly chest radiography should be performed 1
- For suspected GI infection: CBC may be indicated for severely ill residents or if symptoms persist beyond 7 days 1
The evidence clearly shows that CBC testing in SNF residents should be guided by clinical suspicion of infection rather than performed on a routine schedule, with the goal of improving patient outcomes through appropriate diagnosis and treatment of infections.