How many diagnostic tests is too many? For one health system, researchers found that separate fungal blood cultures are redundant, and possibly removing them from a standard order could save the system a bit of money.
In exchange, the researchers recommend targeted use in high-risk patients.
Double Tests
The researchers—led by Logan Brock, PharmD, an antimicrobial stewardship and infectious diseases clinical pharmacist at Manning Family Children’s, in New Orleans, who was at University of Florida Health at the time of the study—collected data from UF Health Shands Hospital, in Gainesville, retrospectively. They analyzed all adult inpatient blood culture collections with paired empiric fungal cultures between Jan. 1, 2023, and Dec. 31, 2024. Of 2,073 patients, 45% identified as female, 69% identified as white, and the median age was 60 years. Most of the patients (60%) were in the ICU at the time of the cultures.
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For testing, they use the BD Myco/F Lytic medium and monitor for growth for 28 days via the BD BACTEC Blood Culture System, Dr. Brock said. “Standard blood cultures were collected on BD standard aerobic and anaerobic medium and incubated for five days through the same system,” he explained.
When did the tests identify a fungus? Out of more than 2,000 tests, fungal growth was found only 64 times. The researchers observed fungal growth in 12.5% of fungal blood cultures that was not detected in routine blood cultures. Alternatively, 46.9% of routine blood cultures had fungal growth that was not found in the paired fungal blood cultures. A little more than 40% of cultures were both positive for fungal growth. Nearly all of the fungal growth was Candida species.
Potential Cost Savings
The researchers also found that the hospital spent a little more than $3,100 on fungal testing to find those 12.5% that were only discovered via fungal cultures and not the standard blood cultures. Combined with the low yield of the tests, Dr. Brock told Infectious Disease Special Edition that they are considering cutting back on some fungal blood cultures—but not doing away with cultures completely. “[Fungal cultures] may not be suitable for empirical use. We are considering restricting the use of fungal blood cultures to patients at higher risk, such as those with certain institutional derived risk factors (e.g., presence of a central venous catheter, immunocompromise, or a history of invasive fungal infection) to improve diagnostic stewardship, but have not finalized any specific criteria yet,” he said.
They are going to keep using standard blood cultures, he continued. “The overall incidence of fungemia was low, and standard blood cultures had a respectable yield,” he said.
However, it’s not just blood cultures that are used for fungal diagnostics. Occasionally, they use non–culture-based testing, he said, like serum 1,3-beta-D-glucan testing, urine histoplasma antigen testing, or metagenomic next-generation sequencing (Karius), “in situations where the team feels it is appropriate.”
Dr. Brock, who presented his work at MAD-ID 2025 (abstract 46 OR FRS), reported no relevant financial disclosures.