Haematocrit from two analysers¶

Apparent heaping in haematocrit is two analysers with different resolutions, identifiable record by record from the co-timestamped panel.

Background¶

• Lab analytes are machine-reported, so most should show a single resolution.
• Haematocrit looked like the exception: about a quarter of values are whole numbers, and its coarser share is 32.4% against 10% expected.

Data¶

• 58,489 haematocrit results in lab_data.csv, with the source taken from the panel sharing the timestamp (blood-gas panels contain pH).
• 1,328 pairs where a blood gas precedes a CBC by up to 15 min.

Method¶

• Split results by source before screening: stamped with pH and blood gases means the theatre blood-gas analyser; stamped with Hb, WBC and platelets means the central CBC analyser.
• Checked the last-digit distribution and heaping at 5 and 10 within each source.
• Compared resolutions of the other analytes both sources report (glucose, Na, K, iCa, lactate).

Results¶

• CBC analyser (43,939 results): 0.1 % resolution, every decimal digit at 10%, so no rounding.
• Blood-gas analyser (14,550 results): always whole percent; the last digit is flat (9.4–10.6% each) and counts vary smoothly, so no heaping at 5 or 10.
• Where a blood gas precedes a CBC by up to 15 min, the blood-gas haematocrit reads 0.8 % lower on average (SD 2.8 %).
• The other shared analytes have matching resolutions between sources, so only haematocrit needs a source rule.

Discussion¶

• There is no rounding model to fit. The registry gives haematocrit a source-dependent resolution (0.1 % or 1 %, anchor nearest), and the API decides the source from the panel.
• This is a third kind of mixed resolution, after people writing values in (height) and two scales (weight).
• The 0.8 % offset is a method difference (conductivity against a counted cell volume), not a resolution issue. It belongs in measurement variability if needed.

Limitations¶

• Nine stand-alone haematocrits (no other analyte at the same time; values 0.0–27) have unknown source. They are probably body-fluid samples and return the two-analyser mixture with flag stand_alone_probable_body_fluid.

Tags: from the resolution work