The optimized CO-rebreathing method

Determination of Hb-mass using the optimized CO-rebreathing method was first described by Schmidt and Prommer in 2005 and was slightly modified by independent scientists the following two years (Gore et al., 2016; Prommer and Schmidt, 2007). The principle of the method is based on the inhalation of a small amount of carbon monoxide (CO) that quickly diffuses from the lungs into the blood where it directly binds to the hemoglobin molecule. The resulting percentage increase of CO bound to hemoglobin (COHb) is inversely proportional to the Hbmass of the person examined. This means that the higher the COHb (%) increase the lower the volume of distribution and therefore, the lower the mass of hemoglobin. To be able to accurately determine Hb-mass the following aspects must be considered:

  1. A precise amount of CO needs to be administered
  2. The inhaled CO must be evenly distributed throughout the bloodstream 
  3. During the test, the amounts of CO being exhaled must be determined 
  4. The amount of CO diffusing from the bloodstream to other tissues must be known.


Below is a brief explanation of the CO-rebreathing procedure:

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A bolus of pure (99.97%) CO is administered to the subject using a Spirometer (SpiCO). This bolus, along with 3 liters of 100% O2, is inhaled for 2 minutes. The amount of administered CO depends, inter alia, on gender, training, and health status. CO administered normally amounts to between 0.8 and 1.2 ml/kg body mass. Arterialized capillary blood samples are taken from a hyperemized earlobe before and, exactly 7 minutes after, the rebreathing procedure and are analyzed using a CO-oximeter. Alternatively, also venous blood samples can be used (Garvican et al., 2010). After the subject is disconnected from the Spirometer, end-tidal CO is assessed before and 2 minutes after the rebreathing procedure using a portable CO detector to determine the CO-volume exhaled. The amount of CO that diffused to myoglobin and other body sites is determined using special formulas that are described by Prommer and Schmidt (2007).

 The total test procedure takes approximately 10-15min. The reliability, expressed as a typical error, is 1.0% – 1.6%.

Technical equipment

To be able to perform the optimized CO-rebreathing method with SpiCO as described by Schmidt and Prommer (2005) and the slightly modified CO-rebreathing method by Gore et al. (2016) and Prommer and Schmidt (2007), you need the following equipment:

The Starter Kit

The Starter Kit is designed for new customers. It simplifies setting up the method in your lab because it contains all the necessary equipment and consumables along with our knowledge gained from more than 15 years of experience. Additional technical equipment is not included. 

The Starter Kit 100 includes the following items:

  • 1 custom-made glass Spirometer
  • 100 Mouthpieces
  • 100 Anti-bacterial filters
  • 10 Rebreathing bags (3 L)
  • 10 Nose clips
  • 1 Syringe set to administer CO
  • Calculation software
  • Online Manual
  • Online Video Tutorial
  • Technical Support
  • Access to the online member area

The consumables last for 100 measurements.

Important note:
The Spirometer is not considered to be medical equipment. Its application is therefore only allowed for healthy subjects and scientific purposes. If you would like to use the method with patients, please contact us to discuss how to make this possible.

A blood gas analyser is required to analyse the carbon monoxide concentration bound to hemoglobin (COHb%). The accuracy of the blood gas analyser should not be less than ± 0.1%. We have had good experiences, in terms of accuracy, with analysers produced by Radiometer (ABL 80/90) and Siemens (Rapid). 

A CO gas tester is required to measure the CO gas concentration in the exhalation air around the mouth and nose during the test procedure. The tester should have a measurement range of at least 0-2000ppm and a resolution of 1ppm. We currently recommend the Dräger PAC 6500. Should you decide to work with the Dräger PAC 6500, you also need to order the calibration adapter, one-way mouthpieces, and corresponding flexible tubes.

The marker gas carbon monoxide should at least have a purity of 3.7 (99.97%). You need ~120-200ml CO for each measurement and the flushing of the syringe (3 x 30-40ml). We recommend small bottles (e.g., 1 Litre, 12 Bar) for security reasons. The oxygen should be suitable for medical use.

Please use a type of soda lime that does not lead to the formation of carbon monoxide during the rebreathing procedure. We recommend using Drägersorb Free.

Prices and support

Starter Kit 100: 3395,-€ (Value Added Tax (VAT) not included)*
Additional Spirometer: 745,-€ (VAT not included)*

Additional Spirometers are helpful in case you plan to perform multiple measurements in a row since the Spirometer must be cleaned, disinfected, and dried after every use. This process takes a minimum of 30min. 

*Please note that shipping and handling fees are not included in the prices above.


Schmidt W, Prommer N. The optimised CO-rebreathing method: a new tool to determine total haemoglobin mass routinely. Eur J Appl Physiol. 2005 Dec;95(5-6):486-95. doi: 10.1007/s00421-005-0050-3.

Gore CJ, Bourdon PC, Woolford SM, Ostler LM, Eastwood A, Scroop GC. Time and sample site dependency of the optimized CO-rebreathing method. Med Sci Sports Exerc. 2006 Jun;38(6):1187-93. doi: 10.1249/01.mss.0000222848.35004.41.

Prommer N, Schmidt W. Loss of CO from the intravascular bed and its impact on the optimised CO-rebreathing method. Eur J Appl Physiol. 2007 Jul;100(4):383-91. doi: 10.1007/s00421-007-0439-2.

Garvican LA, Burge CM, Cox AJ, Clark SA, Martin DT, Gore CJ. Carbon monoxide uptake kinetics of arterial, venous and capillary blood during CO rebreathing. Exp Physiol. 2010 Dec;95(12):1156-66. doi: 10.1113/expphysiol.2010.054031.