Positive blood culture
at the bedside
- on the call → patient name and file number, Gram stain, how many sets of how many, from a line or a vein, time taken; read it back
- then the patient → airway, breathing, circulation; full vitals; sick or well
- drug chart → current antibiotic, does it cover this Gram stain, allergies, renal function
escalate now if
- hypotension, confusion, rising lactate → sepsis, antibiotics now → fever, hypotension
- Gram-positive cocci in clusters in a sick patient, or S. aureus named → treat as S. aureus
- Gram-negative rods → cover now
- yeast → candidemia
- neutropenic → febrile neutropenia → fever
differentials
- always real → S. aureus, Gram-negative rods, yeast, S. pneumoniae, beta-hemolytic streptococci
- often a contaminant → coagulase-negative staphylococci, Micrococcus, Bacillus, Cutibacterium, Corynebacterium, especially in one set of two
- the same organism can still be real → two or more sets, a central line, a prosthetic valve or device, neutropenia, or an unwell patient
focused check
- source → line sites, wounds, urine, chest, abdomen, joints, back pain, new murmur
- hardware → central line, dialysis catheter, pacemaker, prosthetic valve or joint
- history → previous cultures and resistant organisms (MRSA, ESBL, CRE)
send now
- two new sets → before changing antibiotics; line in place: one from the line, one from a vein
- CBC, CRP, RFT, lactate → if unwell
- sensitivities → follow up with microbiology; note when they are due
treat
Gram-positive cocci in clusters
- unwell, line or prosthesis, or more than one set → vancomycin 25 mg/kg IV load → vancomycin
- S. aureus confirmed → ID consult, repeat cultures until negative, echocardiogram, remove infected lines; MSSA → cefazolin 2 g IV q8h; never a contaminant
- one set, well, no line or prosthesis → likely contaminant; repeat two sets, no vancomycin yet; discuss with microbiology
Gram-negative rods
- not covered → piperacillin-tazobactam 4.5 g IV q6h or cefepime 2 g IV q8h; ESBL history or shock → meropenem 1 g IV q8h → empiric antibiotics
- find the source: urine, abdomen, line
Gram-positive cocci in chains or pairs
- usually real; check coverage; new murmur, prosthetic valve or Enterococcus → senior and ID
yeast
- never a contaminant; caspofungin 70 mg IV then 50 mg daily, or micafungin 100 mg IV daily
- central line the likely source → remove it as early as possible; ID consult; repeat cultures daily or every other day until clear; dilated eye exam within the first week
- sensitivities back → narrow; resistant organism or unsure → senior and microbiology or ID
- hand over → organism, sets, antibiotic started or changed, repeat cultures, sensitivities due
evidence
| source | type |
|---|---|
| JAMA 2025 · Management of S. aureus bacteremia ↗︎ | review |
| IDSA 2016 · Candidiasis ↗︎ | international guideline |
| Clin Microbiol Rev 2019 · Blood culture contamination ↗︎ | review |
Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.
free the on-call checklist covers the whole shift on one printable page.
studying for the IM exam? the IM Rapid Review covers this in the same format. see the sample chapter.
updated Oct 2026file lab/positive-blood-culture