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Adjust a measured DLCO / TLCO for the patient's hemoglobin

Source: R/dlco_hb.R
pft_dlco_hb_correct.Rd

Applies the Cotes 1972 hemoglobin correction to a measured carbon monoxide transfer factor (DLCO or TLCO), returning the value that would have been measured if the patient's hemoglobin equaled the age- and sex-specific reference. The correction is intended for clinical interpretation: after applying it, the corrected DLCO can be passed to pft_diffusion() (whose reference equations assume the reference Hb).

Usage

pft_dlco_hb_correct(dlco, hemoglobin, sex, age = NA_real_)

Arguments

dlco

Numeric vector of measured DLCO or TLCO values, any unit system (the correction is multiplicative and unit-agnostic).

hemoglobin

Numeric vector of measured hemoglobin in g/L (routine clinical adult range 120-160 g/L). Pass g/L directly; the function does not detect or convert g/dL inputs.

sex

Character vector ("M"/"F"). Soft-corrected via the internal normalize_sex_vec() helper so "Male", "female", etc. work.

age

Optional numeric vector. When supplied, males aged < 15 yr use the female / child reference (134 g/L) per Stanojevic 2017 p. 11. When omitted (the default NA_real_), males default to the adult reference (146).

Value

Numeric vector of Hb-corrected DLCO / TLCO values, same units as dlco. NA propagates from any input.

Details

Stanojevic et al. ERJ 2017 explicitly recommends (Table 4 p. 9) that the published GLI TLCO reference values be uncorrected for Hb, with Hb levels considered separately during interpretation. This function provides that interpretive step.

Formula (Cotes 1972; reformulated from Stanojevic 2017 p. 9, with constants 1.7 and 0.7 reflecting the membrane / capillary diffusing capacity ratio of 0.7 mL min^-1 mmHg^-1 mL-blood^-1):

$$TLCO_{Hb} = TLCO_{measured} \times \frac{1.7 \cdot Hb_{ref}}{Hb + 0.7 \cdot Hb_{ref}}$$

Reference Hb levels (Stanojevic 2017 p. 11):

  • Males aged >= 15 yr: 146 g/L

  • Females (any age) and children < 15 yr: 134 g/L

When hemoglobin == Hb_ref the correction factor is exactly 1 (no adjustment). Anaemic patients (hemoglobin < Hb_ref) receive an UPWARD correction reflecting that less Hb means less CO uptake and a depressed measured value.

References

Stanojevic S, Graham BL, Cooper BG, et al. Official ERS technical standards: Global Lung Function Initiative reference values for the carbon monoxide transfer factor for Caucasians. Eur Respir J. 2017;50(3):1700010. doi:10.1183/13993003.00010-2017 . Hb correction is discussed on p. 9 and the Cotes formula context on p. 11.

Cotes JE, Dabbs JM, Elwood PC, et al. Iron-deficiency anaemia: its effect on transfer factor for the lung (diffusing capacity) and ventilation and cardiac frequency during sub-maximal exercise. Clin Sci. 1972;42:325-335.

See also

pft_diffusion() for the reference-value computation that consumes the Hb-corrected DLCO.

Examples

# An anaemic adult male (Hb = 100 g/L vs reference 146 g/L) with
# measured DLCO of 20 mL/min/mmHg has a Hb-adjusted DLCO of
# 20 x (1.7 x 146) / (100 + 0.7 x 146) ~= 24.55.
pft_dlco_hb_correct(dlco = 20, hemoglobin = 100,
                    sex = "M", age = 40)
#> [1] 24.54995

# No-op when Hb equals reference.
pft_dlco_hb_correct(20, hemoglobin = 146, sex = "M")
#> [1] 20

# Children use the female / child reference (134 g/L) regardless
# of sex.
pft_dlco_hb_correct(20, hemoglobin = 134, sex = "M", age = 10)
#> [1] 20