The recommendation is to use a recent Hb value. The question is; what is recent enough? Even a value that is no more than a few weeks old may not be accurate enough.

“The Hb value may not vary much in healthy individuals, but in a clinical setting, by definition, we don’t deal with healthy people. In hematology patients, the Hb value varies quite a lot and if a patient has just had a blood transfusion, the Hb value will be very different than just a week earlier”, says Herman Groepenhoff.

Before they had the ability to perform Hb tests themselves in their own department, he admits that his colleagues and he sometimes used Hb values that were more than a month old.

“The Hb values tended to get older and older just because we wanted to avoid the hassle of doing a venous puncture and having to go to the lab to have it analyzed.”

For two years Herman Groepenhoff and his colleagues have used the HemoCue^® Hb 201 system and now they check the patients’ Hb values for every diffusion test they do. According to him, it is satisfying knowing that they follow the European Respiratory Society guidelines when they correct for an updated Hb value each time. Another advantage is that it saves time. The diffusion test is repeated at least twice. During the four minute break between tests, a finger stick can be performed for determination of the Hb value, which can be entered into the computer that is used for calculation of the diffusion capacity.

Since Herman Groepenhoff´s department started using the Hb 201 system, they have found that for Hb values within the normal range, correction for Hb may not be that critical. For values outside the normal range though, it is. There are also quite a few other things that can interfere with the outcome of a diffusion capacity test. If the patient instead of inhaling as much as he or she can, only inhales 90 percent, or holds his or her breath for eleven seconds instead of ten, the variation is already there.