What lab timestamps mark¶

Merged into "What the lab timestamp marks" on 18 October 2026; kept so old links still work. The original finding: central-lab timestamps most likely mark specimen receipt in the lab, about 10 minutes after the draw.

Background¶

• Lab times are machine timestamps at 1 s resolution, with no rounding to model. The seconds component is spread evenly (about 1.7% per second).
• The working hypothesis was that they mark when the result was returned.

Data¶

• lab_data.csv: 131,942 unique timestamps.
• Intra-operative central-lab timestamps (to 30 min after anaesthesia end) with a blood gas in the preceding hour: CBC 1,665, coagulation 1,539, chemistry 1,613.

Method¶

• Compared timestamps of panels run on different analysers in the same case.
• Checked for a consistent order of draw between panels.
• Measured the lag from a point-of-care blood gas to the next central-lab panels.
• Checked the time of day of ward CBCs, and the minute of the hour for heaping.

Results¶

• Each panel has one timestamp for all its analytes. Panels drawn together are stamped within seconds of each other (75% of CBC–chemistry pairs within 60 s), centred on zero and in no fixed order.
• There is no consistent order of draw: each panel is equally likely to be first.
• Central-lab panels after a blood gas are stamped a median of about 10 min later (about a quarter within 5 min and three-quarters within 15 min). The lag is the same for CBC, coagulation and chemistry.
• Ward CBC timestamps peak at 08:00–09:00, after a typical early-morning phlebotomy round.
• The minute of the hour varies smoothly, with no spikes at 0 or 5.

Discussion¶

• Result times would differ by analyser turnaround, with chemistry later than CBC. They do not, which rules that out.
• For the API, lab times are single resolution (1 s, anchor floor). A central-lab timestamp should carry a backward lag of about 10 min (95% within about 30 min) to the sampling time; a blood-gas timestamp needs a few minutes at most.

The same question from the timing side: What the lab timestamp marks.

Limitations¶

• The conclusion assumes that a blood gas and central-lab tubes are often drawn together.

Open questions¶

• Receipt hypothesis against flush artefacts (next step). The receipt hypothesis should be checked against arterial-line flush artefacts in the waveforms, or by asking the VitalDB team.

Tags: from the resolution work