Two sets of blood cultures, from two sites — and the sepsis clock does not stop for them

Take two sets of blood cultures from separate venepuncture sites before the first dose of antibiotic. Two sets is what lets you distinguish a true bacteraemia from a skin contaminant, and separate sites is what makes that distinction interpretable. A single set drawn from a line, or from the same vein twice, answers a different and weaker question.

The rule that matters alongside it is that culture-taking must not delay treatment in a patient who is septic. If cultures cannot be drawn within a few minutes, give the antibiotic and take them afterwards, documenting that you did so. Yield falls after the first dose, but a delayed antibiotic costs more than a lost culture. The failure mode worth naming is the middle path — a registrar making repeated attempts at a difficult patient while the prescription sits unsigned.

• Two sets, two separate venepuncture sites, before the first dose where possible
• Draw adequate volume — under-filled bottles are the commonest reason a true bacteraemia is missed
• If access is difficult, give the antibiotic and take cultures after, and record that sequence
• Note in the chart which set came from a line, if any did
• Do not repeat cultures reflexively at 24 hours unless the answer would change management

Why it matters

The commonest reason a bacteraemia cannot be interpreted is not the timing but the number of sets and the volume drawn.

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