Results of a Prospective Study Evaluating a Noninvasive Method of Hemoglobin Adjustment for Determining the Diffusing Capacity of the Lung.

Rationale: Measurement of the diffusing capacity of the lung for carbon monoxide (D-LCO) is significantly influenced by the pulmonary capillary blood volume. Consequently, measurements require adjustment for blood hemoglobin concentration (D-LCOadj) to allow meaningful clinical interpretation. Noninvasive point-of-care devices that measure hemoglobin transcutaneously provide immediate values for hemoglobin that may be useful in pulmonary function laboratories for determining D-LCOadj. Objectives: To test the hypothesis that D-LCOadj determinations obtained with a commercially available device for noninvasive, point-of-care measurement of blood hemoglobin concentrations are not significantly different from determinations obtained using hemoglobin concentrations measured conventionally in venous blood samples. Methods: In a prospective open trial, hemoglobin measurements were obtained with the Pronto-7 spot check pulse CO-oximeter (Massimo, Irvine, CA) and by venipuncture for 205 patients referred for DLCO testing at Cincinnati Children's Hospital. Hemoglobin and D-LCOadj measurements were compared between the two methods, using Student paired t tests and Bland-Altman plots. To assess variability, the differences in D-LCOadj between the two methods were also compared by a modification of the current standard for acceptable within-session variability for D-LCO. Clinical interpretation for individual D-LCO tests based on D-LCOadj values obtained from the two methods were compared statistically using Kendall's coefficient of concordance to determine whether the Pronto-7 altered the classification of the severity of D-LCO defects. Measurements and Main Results: Measurements of hemoglobin concentration by the Pronto-7 analyzer were significantly lower than those obtained from venipuncture blood samples (13.16 1.8 vs. 13.462.0; P = 0.01). However, there were no differences for D-LCOadj between bothmethods (23.667.7 vs. 23.767.5ml/min/mm Hg; P = 0.42). There was strong correlation between the Pronto-7 and venipuncture D-LCOadj values (r = 0.99, P< 0.0001). Variability between the two methods was low for D-LCOadj, with a bias of -0.07. More than 96% of tests met acceptable within-session variability. There was no significant difference in the clinical interpretation of the D-LCO test based on D-LCOadj values recovered from both methods (Kendall's coefficient, 0.96). Conclusions: Noninvasive measurement of hemoglobin for determination of D-LCOadj was accurate and provided acceptable within-session variability. The results obtained noninvasively did not alter clinical interpretation of test results compared with venipuncture. These findings support noninvasive point-of-care devices as an alternative to venipuncture for determining hemoglobin to measure D-LCOadj in most patients.