When I was a resident (Not that long ago people! Come on!!), I was taught by Dr. Mattu (@amalmattu) that the WBC Count is “the last bastion of the intellectually destitute.” These words were meant to encourage me to avoid reflexively ordering a WBC to determine whether a patient had “an infection.”  Often, it is aimed at the evaluation of the patient with abdominal pain and possible appendicitis. Recently, there have been other labs that have be used in a similar fashion (ex, Lactate Level), but the WBC count still has a strong association, in many people’s minds, with “infection” or general “sickness.” Some days I spend half of my clinical time discussing my disdain for the WBC count and this perceived association. Recently, one of my fantastic PEM Fellows, Dr. Mary Grady, alerted me to an article published that helps add justification for my position and Dr. Mattu’s mantra. Let’s review the Accuracy of WBC Count in Evaluation of Fever:

The WBC Count: Beliefs

• Our patients’ perceive the WBC Count as being useful measure of health.
  • Abnormal WBC = Badness; Normal WBC = Wellness.
  • A quick internet search of “WBC Count” will lead you to the conclusion that an abnormal WBC count is:
    • Concerning.
    • Associated with infection…
    • Also associated with Inflammation, Trauma, Allergy, “Disease.”
  • I wouldn’t classify this as “Alternative Facts,” but it is certainly not the entire story and we need to realize that our patients are consuming this information prior to seeing us in the ED.

• We are part of the problem.

Ok, before we get on our high horses and ride off into the sunset. realize that the misconceptions of medical testing are our creations… and reinforced by our poor communication.

• • We like certainty and dislike difficult conversations.
    • Obtaining tests, and playing the favorable odds of them supporting our already formed conclusions, is often easier than discussing the limitations of tests.
    • It is difficult to discuss sensitivities and specificities of lab tests, particularly when I have a hard time understanding that myself.
    • It is also difficult to discuss uncertainty and describe reasonable approaches to mitigating risk.
  • We like to please people…
    • Many people want “something done” and testing is typically equated with “doing something.”
    • Spending a few minutes education patients/families can really help realign everyone’s goals… and is actually “doing something.”
      • There may be a perception that they need a Plastic Surgeon, but that facial laceration is best closed by me at 3am.
      • There may be a perception that their child needs IV fluids for dehydration, but they need to be educated about the potential pitfalls of that as well as how Oral Rehydration Therapy is faster.
  • We have been conditioned.
    • Just like a Pavlovian response, many of us have had our medical training link “Infection” with “Abnormal WBC Count.”
    • Each time I was asked for the WBC count when discussing a child with appendicitis a subconscious link was generated.
    • It takes effort to decondition the Pavlovian Response.

The WBC Count: Not Alternative Facts

• Abnormally high or low WBC counts can be important when…
  • Considering Neutropenia.
  • Considering a hematologic oncologic processes, like Leukemia.

• Isolated abnormal WBC Count is not often helpful in ruling in or out a diagnosis.
  • Isolated abnormal WBC does not equate to Septic Arthritis, and it’s absence doesn’t negate the diagnosis.
  • Appendicitis can exist with normal WBC count and abnormal WBC count does not diagnose appendicitis.
  • The clinical question helps determine the utility of the test.

The WBC Count: Fever Evaluation in Infants

• Fever is one of the most common presenting complaints in children in the ED.
• The CBC is the most commonly obtained test in their evaluation.
• In September of 2017, JAMA published a PECARN study that looked at the Utility of the CBC for Evaluation of Fever in Infants. [Cruz, 2017]
  • Design:
    • Prospective enrollment of infants <61 days of age in 26 EDs
    • Included infants with fever, Blood Cultures, and CSF cultures (or telephone follow-up)
    • Excluded critically ill and premature and those with significant comorbidities or recent antibiotic exposure.
  • Found:
    • Of the 4313 who met inclusion criteria, 97 (2.2%) had invasive bacterial infections (bacteremia or meningitis — not UTI).
      • Bacteremia – 73
      • Meningitis – 24 (11 with concurrent bacteremia)
      • 57 were Neonates (< 29 days of age) – 4.3% of neonates
      • 40 were 29-60 days of age – 1.4% of this group.
    • No CBC parameter (leukocytosis, leukopenia, ANC, thrombocytosis) distinguished between infants with invasive bacterial infections and those without infection.
    • Using widely accepted normal ranges for WBC counts would have missed 63% of cases.
  • Conclusions:
    • A minority of infants with invasive bacterial infections have abnormal WBC counts.
    • WBC count is a poor discriminator of infants with and without invasive bacterial disease in the post-vaccination era.
    • “… we need to question our continual reliance on a test whose greatest strength may simply be in its ready availability in clinical practice.” [Cruz, 2017]

Moral of the Morsel:

• The WBC Count is still the last bastion of the intellectually destitute. It does not equate to presence or lack of infection.
• No test is perfect. All must be performed in relation to a clinical question and compared to pre-test probabilities.
• Educate others! Take the time to discuss with your patients/families about the real limitations of testing.

References