CBC Testing Guidelines for Older Adults in Skilled Nursing Facilities

Indications for CBC Testing

The American Geriatrics Society recommends CBC with differential should be performed when infection is suspected based on clinical presentation, not as a routine screening test 1, 2, 3
The Infectious Diseases Society of America suggests testing should be completed within 12-24 hours of symptom onset, or sooner if the resident is seriously ill 1, 4
The American Geriatrics Society prefers the manual differential to assess bands and other immature forms of white blood cells 1, 4

An elevated WBC count (≥14,000 cells/mm³) warrants careful assessment for bacterial infection, with or without fever, according to the Infectious Diseases Society of America 1, 5
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, as stated by the American Geriatrics Society 4, 5
Leukocytosis with a WBC count >14,000 cells/mm³ has a likelihood ratio of 3.7 for detecting bacterial infection, as reported by the Infectious Diseases Society of America 5

The American Geriatrics Society recommends advance directives should be reviewed prior to any intervention, including laboratory testing 4, 3
The American Geriatrics Society suggests if specific diagnostic measures are consciously withheld, the reasons should be documented in the medical record 4, 3
The Infectious Diseases Society of America states tests should only be performed if they have reasonable diagnostic yield, are low risk, reasonable in cost, and will improve patient management 5

The Infectious Diseases Society of America advises avoiding routine or scheduled CBC testing in asymptomatic residents, as this leads to unnecessary costs and potential false positives 2, 5
The American Geriatrics Society warns not to rely solely on CBC results to rule out infection, as typical symptoms and signs of infection are frequently absent in older adults 4, 3
The American Geriatrics Society notes basal body temperature decreases with age and frailty, making classic definitions of fever less reliable in this population 4, 3
The Infectious Diseases Society of America recommends avoiding ordering CBCs when results will not change management decisions 5

For suspected UTI: The American Geriatrics Society and the Infectious Diseases Society of America recommend 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) 2, 4
For suspected pneumonia: The Infectious Diseases Society of America suggests CBC with pulse oximetry and possibly chest radiography should be performed 1, 2
For suspected GI infection: The Infectious Diseases Society of America states CBC may be indicated for severely ill residents or if symptoms persist beyond 7 days 1, 6

In the absence of fever, normal WBC count, no left shift, and no specific clinical manifestations of focal infection, additional diagnostic tests may not be indicated due to low potential yield, as recommended by the Infectious Diseases Society of America 7
The Infectious Diseases Society of America recommends that clinical symptoms and signs should guide further evaluation when WBC count is within normal range 7

For suspected infection with normal WBC, evaluate for left shift in the differential count, which may indicate bacterial infection despite normal total WBC, and consider clinical presentation and other vital signs, especially fever patterns in older adults 7
Consider clinical presentation and other vital signs, especially fever patterns in older adults, as recommended by the Infectious Diseases Society of America 8
For older adults in long-term care facilities, temperature readings of >100°F (37.8°C), >2 readings of >99°F (37.2°C), or an increase of 2°F (1.1°C) over baseline should prompt further evaluation even with normal WBC 8, 9

Even with normal total WBC count, assessment of differential is crucial, and manual differential is preferred to assess bands and other immature forms, as recommended by the Infectious Diseases Society of America 7