Should labs be ordered?

Laboratory Testing Should Be Guided by Clinical Assessment, Not Performed Routinely

Laboratory tests should only be performed if they have reasonable diagnostic yield, are low risk, reasonable in cost, and will improve patient management, rather than ordering routine or "shotgun" panels without specific clinical indications. 1

Appropriate Laboratory Testing Approach

Initial Assessment

• A complete blood count (CBC) with differential should be the primary initial laboratory test for patients with suspected infections 1
• Significant findings that warrant careful assessment for bacterial infection:
  • Elevated WBC count (>14,000 cells/mm³) - likelihood ratio 3.7 1
  • Left shift (bands >16% or total band neutrophil count >1,500 cells/mm³) - likelihood ratio 14.5 1
  • High percentage of neutrophils (>90%) - likelihood ratio 7.5 1

Evidence-Based Approach to Laboratory Testing

The Infectious Diseases Society of America (IDSA) guidelines clearly state that diagnostic tests should only be performed if they:

• Have reasonable diagnostic yield
• Are low risk
• Are reasonable in cost
• Will improve patient management 2

In adult patients with primary psychiatric complaints, the American College of Emergency Physicians recommends that diagnostic evaluation should be directed by the history and physical examination. Routine laboratory testing of all patients is of very low yield and need not be performed as part of the assessment. 2

Specific Testing Recommendations by Clinical Scenario

For Suspected Infections

1. CBC with differential should be performed within 12-24 hours of symptom onset (or sooner if the patient is seriously ill) 2
2. 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 2

For Suspected Urinary Tract Infections

• Urinalysis or urine cultures should not be performed for asymptomatic patients 1
• Only test non-catheterized patients with acute onset of UTI symptoms (fever, dysuria, gross hematuria, new/worsening urinary incontinence) 1
• For catheterized patients, evaluation should only be performed if suspected urosepsis 1
• Uncomplicated UTIs diagnosed by positive leukocyte esterase and nitrite tests can be treated without culture 3

For Respiratory Infections

• If pneumonia is clinically suspected, perform pulse oximetry for patients with respiratory rates >25 breaths/minute
• Order chest radiograph only if hypoxemia is documented (oxygen saturation ≤90%) 1

For Blood Cultures

• Blood cultures have low yield in most cases and rarely influence therapy
• Consider only when bacteremia is highly suspected, quick access to laboratory facilities is available, and capacity to administer parenteral antibiotics exists 1
• When indicated, collect 2-4 blood cultures before starting antibiotics 1

Common Pitfalls to Avoid

1. Ordering "routine" laboratory panels without specific indications

   • Multiple studies have shown that extensive, routine laboratory testing is unnecessary 2
   • False positive laboratory results are 8 times more frequent than true positives in patients with routine testing 2

2. Ignoring pre-test probability

   • Ferguson and Dudleston found that 17% of laboratory test abnormalities were detected, but only 2 results were not predicted by the patients' history and physical examination 2

3. Failing to consider cost-benefit ratio

   • Tests should only be performed if they will cause the clinician to reassess treatment strategy 2
   • Additional diagnostic tests should be performed only for clinical presentations that are unusual or that fail to respond to initial therapy 2

4. Not reviewing advance directives

   • Advance directives should be reviewed prior to any intervention 2
   • Consider limiting diagnostic studies in severely debilitated patients with poor survival prognosis, unless risk exists to other residents and staff 1

Laboratory testing should be targeted and guided by clinical assessment rather than performed routinely. This approach ensures appropriate resource utilization while maintaining quality patient care.