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EIN members recently discussed the appropriate use of non-microbiologic diagnostic tests, including complete blood counts (CBCs), for infectious diseases.
A member in Florida began the discussion, asking about “the necessity of frequent CBCs on hospitalized patients admitted with infectious diagnoses, for the most part general ID issues (not neutropenic or in the intensive care unit [ICU]). Under what circumstances would you want frequent CBC monitoring (i.e., aside from disseminated intravascular coagulation [DIC] from sepsis and hemolysis from infections such as malaria)?”
A respondent in Minnesota noted that “the same could be asked about inflammatory markers (erythrocyte sedimentation rate [ESR], C-reactive protein [CRP], procalcitonin). The trend curves look nice and make us feel good,” the member wrote. “But do they add meaningfully to the bedside clinical assessment?”
An EIN member in Canada reported CBC monitoring “not often and based mostly on clinical assessment first,” sometimes in cases of a fever not yet diagnosed, if the patient’s initial white blood count (WBC) was extremely high, if there is concern about development of hemolytic-uremic syndrome (HUS) in a patient with colitis, or with malaria.
“I've always thought that in general, we order too many CBCs and too many chemistry panels on stable patients,” a member in New Hampshire responded. “I’ll check a CBC more frequently when there are significant abnormalities to begin with (low platelets, for example), or when the patient has a high risk of other complications (septic patient in the ICU, not responding to treatment).”
Short of that, a CBC every two to three days while the patient is in-house is usually reasonable, the member continued, and “maybe not at all when following a patient with something like cellulitis or pneumonia, who is obviously improving and ready for oral antibiotics.”
Daily CBC or electrolyte monitoring do not make sense in regular day-to-day admissions, another member in Canada wrote, “and I don’t mean only for infectious disease related issues. Eventually, the iatrogenic drop in hemoglobin might change our clinical management, but this is avoidable.”
“The only time we ask for regular CBCs is when we treat our patients with long-term high-dose beta-lactam antibiotics (e.g., for osteomyelitis) to monitor drug-induced neutropenia,” the member noted, “and when we start an HIV-exposed newborn on azidothymidine (AZT) to monitor anemia, and this is at most a weekly CBC. I suppose that CBC monitoring with linezolid treatment is also warranted, but we haven’t needed to use this in children.”
For most uncomplicated infectious illnesses, two WBCs are needed, one to assist with initial diagnosis and/or to demonstrate that the patient is having the expected response, and another to document that the WBC is consistent with clinical recovery, an EIN member in Pennsylvania wrote.
“It’s not necessary to get daily WBCs (or chemistry panels or chest x-rays, etc.) in a patient with a solid clinical diagnosis who is clinically improving,” the member continued. “Many of our residents get daily labs regardless of the patient’s clinical progress. This is wasteful, expensive, hard on the patient’s antecubital fossae, and a barrier to learning the essentials of critical thinking.”
A respondent in Tennessee agreed: “‘Following the white count daily’ is almost never helpful in monitoring the clinical course of patients with infectious diseases. In situations where laboratory test results can provide additional evidence of adequate response to therapy, monitoring acute phase reactants, such as C-reactive protein, is much more likely to be of value.”
“Some doctors order daily CBC and differential when CBC without differential is often adequate in many non-ICU patients,” an EIN member in California responded. “We are often asked to do consults for leukocytosis and frequently find the reason.
A consensus on when CBC monitoring is appropriate could lead to savings, the member suggested, although “one would have to balance cost savings with fewer CBCs against missed changes in patient conditions with daily CBC that might interfere with patient care or eventually lead to higher costs.”
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The Emerging Infections Network (EIN) is a provider-based sentinel network designed to help the public health community detect trends in emerging infectious diseases.
A joint project of IDSA and the Pediatric Infectious Diseases Society (PIDS) with funding from the Centers for Disease Control and Prevention (CDC), EIN tracks emerging infectious diseases and keeps the public health community up to date with new disease trends, difficult cases, and other issues affecting members’ clinical practices. The Network provides a great opportunity for members to share knowledge quickly across large geographical distances. Both IDSA and PIDS members are eligible to join. Click here for more information or to join EIN.
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