HaemoglobinNoninvasive  >  Continuous

Clinical Accuracy

Background – Laboratory Haemoglobin Variability

  • Many clinicians are not familiar with the level of variability that exists in laboratory haemoglobin measurements, both within and between laboratory device models.
  • In a study of 5 different models of laboratory CO-Oximeters, using two of each lab CO-Oximeter, for a total of 10 devices, investigators reported the average standard deviation was 0.5 g/dL over all five devices and the max was 1.2 g/dL.1
Manufacturer Model Radiometer ABL-735 Bayer Rapidlab 860 Nova STP CCX 1 Roche Omni S Instrumentation 682 CO-Oximeter
Bias (g/dL) 0.0 -0.3 -0.8 -0.4 0.4
Standard deviation (g/dL) 0.1 0.2 0.3 0.8 1.2
  • Many clinicians are also not familiar with the level of variability that exists between laboratory haemoglobin methods, because they would rarely have a clinical reason to send the same blood sample to two different lab devices.
  • There is even greater variability when analysing haemoglobin values from two different laboratory methods.
  • The most common method of measuring haemoglobin in the central lab is through a hematology analyser, while in the operating room and ICU it is most often through a CO-Oximeter, the same device used for arterial blood gas measurements.
  • In a study done at the Mayo Clinic, 471 consecutive blood samples during surgery were run on both the central lab hematology analyser as well as the department CO-Oximeter.
  • The results showed two calibrated lab devices analysing sequential blood draws varied up to 2 g/dL.

  • This is significantly greater than most clinicians expect, but it is real variation.
  • Intra- and inter-laboratory device variation is important information to know when assessing a new haemoglobin method like SpHb.

SpHb Accuracy

  • In Masimo's FDA submissions, SpHb has been consistently validated in a range of 8 to 17 g/dL with accuracy of 1.0 g/dL ± at one standard deviation.2
  • An independent study in the surgical intensive care unit evaluated 471 haemoglobin measurements from 62 patients.3
  • SpHb, a satellite laboratory CO-Oximeter (Siemens RapidPoint 405), and a point-of-care device (HemoCue 301) were compared to reference haemoglobin from the central laboratory hematology analyser (Sysmex XT2000i).
    • Satellite lab CO-Oximeter was 0.9 ± 0.6 g/dL (Arms 1.1 g/dL)
    • Point-of-care Hemocue was 0.3 ± 1.3 g/dL (Arms 1.3 g/dL)
    • SpHb was 0.0 ± 1.0 g/dL (Arms 1.0 g/dL)
  • It is worth noting that all methods have outliers.

  • In addition, changes in haemoglobin from the central lab hematology analyser occur when multiple measurements are taken. They can go up, go down, or stay roughly the same.
  • Researchers also evaluated how the changes in satellite lab CO-Oximeter, HemoCue, and SpHb, compare to changes in central lab haemoglobin.
  • Both visually and by the correlation (R value), SpHb trend accuracy was similar to the 2 invasive methods.
  • It is worth noting that all methods have outliers.

All available SpHb studies are listed here.

REFERENCES

  • 1 Gehring H et al. Anesth Analg. 2007;105:S24 -30.
  • 2 Masimo FDA 510(k) Submission Data.
  • 3 Frasca D et al. Crit Care Med. 2011 Oct;39(10):2277-82.