What labs should be ordered in a rapid response situation?

Laboratory Tests to Order in a Rapid Response

In a rapid response situation, essential laboratory tests should include complete blood count, comprehensive metabolic panel, cardiac troponin, coagulation studies, arterial blood gas, and lactate level. These tests provide critical information about the patient's physiologic status and help identify the underlying cause of deterioration.

Core Laboratory Tests for Rapid Response

Immediate Blood Tests

• Complete Blood Count (CBC)

  • Evaluates for anemia, infection, bleeding disorders
  • Includes WBC count with differential to assess for leukocytosis (>14,000 cells/mm³) or left shift (>16% bands) which strongly suggests bacterial infection 1

• Comprehensive Metabolic Panel (CMP)

  • Electrolytes (sodium, potassium, chloride, bicarbonate)
  • Renal function (BUN, creatinine)
  • Glucose (avoid hypoglycemia or hyperglycemia)
  • Liver function tests (AST, ALT, alkaline phosphatase, bilirubin)

• Cardiac Markers

  • Troponin to evaluate for cardiac injury 1
  • ECG should accompany troponin testing

• Coagulation Studies

  • Prothrombin time (PT)/International Normalized Ratio (INR)
  • Activated partial thromboplastin time (aPTT)
  • Essential for patients with bleeding risk or on anticoagulants 1

• Arterial Blood Gas (ABG)

  • Assesses oxygenation, ventilation, and acid-base status
  • Particularly important for patients with respiratory distress or altered mental status 1

• Lactate Level

  • Critical for evaluating tissue perfusion and identifying shock
  • Strong predictor of mortality; levels >3.5 mmol/L early after admission have high specificity (95%) for poor outcomes 2

Situation-Specific Tests

For Suspected Infection

• Blood cultures (two sets from different sites) before antibiotic administration 1
• Procalcitonin if bacterial infection probability is low to intermediate 1
• Urinalysis and urine culture if urinary tract infection is suspected 1
• Respiratory viral panel if respiratory symptoms are present 1

For Neurological Changes

• Toxicology screen
• Ammonia level (if liver disease suspected)
• Consider lumbar puncture if meningitis is suspected (after appropriate evaluation) 1

Optimization of Laboratory Testing

Avoid Routine Daily Testing

The American Thoracic Society recommends against ordering diagnostic tests at regular intervals (such as daily) and instead ordering tests in response to specific clinical questions 1. This approach:

• Reduces iatrogenic anemia
• Decreases unnecessary transfusions
• Lowers costs
• Reduces false positive results

Timing Considerations

• Laboratory specimens should be drawn before initiating intravenous fluids 1
• Blood cultures should be collected before antibiotic administration 1
• For patients with central venous catheters, simultaneous central and peripheral blood cultures should be collected to calculate differential time to positivity 1

Common Pitfalls to Avoid

1. Delaying treatment for test results: Never delay critical interventions (e.g., antibiotics for suspected sepsis) while waiting for laboratory results

2. Over-reliance on normal values: Normal laboratory values don't exclude serious pathology; clinical context is essential

3. Under-ordering in elderly patients: Older adults may present atypically; leukocytosis with or without fever warrants careful assessment for bacterial infection 1

4. Failure to repeat abnormal tests: Initial abnormal results should be followed up appropriately

5. Ordering unnecessary tests: Focus on tests that will change management decisions rather than ordering a standard "panel" for all situations 1

By following this structured approach to laboratory testing during rapid responses, clinicians can efficiently gather critical diagnostic information while avoiding unnecessary testing that may delay care or lead to iatrogenic complications.