Adjusting DLCO for hemoglobin

My hospital’s Oncology division treats a number of patients with lymphoma and leukemia. It also has an active bone-marrow transplant program and for all of these patients diffusing capacity measurements are a critical part of assessing treatment progress. Since these patients are also frequently anemic, correcting DLCO results for hemoglobin is also critical.

For a factor that has as much importance for the interpretation of DLCO results as it does the effect of hemoglobin on DLCO has actually been studied a relatively small number of times. Part of the reason for this is the problem of finding an acceptable model. A reduced or elevated hemoglobin is a consequence of many diseases and conditions. When studying patients longitudinally it is often difficult to separate the changes in DLCO that occur from the disease process and those that occur from changes in hemoglobin. For this reason changes in hemoglobin pre- and post-treatment in anemia and polycythemia have been studied most frequently.

The ATS/ERS currently recommends correcting DLCO for hemoglobin (although notably they recommend that the predicted DLCO be corrected, not the observed value) using the equations developed by Cotes et al in 1972. Cotes’ work was based on subjects with iron-defficienty anemia but just as importantly on theoretical considerations involving Roughton and Forster’s equation on the relationship between the membrane and hemoglobin components of the diffusing capacity:

1_over_DLCO_formula

Cotes

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