Diffusing Capacity Of The Lungs For Carbon Monoxide (DLCO) Correction For Hemoglobin In Anemia Calculator

How does this diffusing capacity of the lungs for carbon monoxide correction for hemoglobin in anemia calculator work?

This is a health tool that aims to correct the tested DLCO in correlation to the level of hemoglobin, a determination that is useful in the cases of patients suffering from anemia and not only.

The equation used by this DLCO calculator is the following:

DLCO Corrected = Predicted DLCO x (1.7 x Hgb / (Age & Sex-Factor + Hgb))

■ The Age & Sex-Factor is 9.38 for females and children, while for males 15 years old or older this factor is 10.22.

■ There are two considerations to be taken into account when using DLCO values and choosing the measurement unit. There are two systems in use: one is the American Thoracic Society (ATS) traditional system where measurements are taken in standard temperature and pressure, dry conditions, also known as STPD, which is mL CO/min/mmHg and the other one is the SI unit in mmol/min/kPa which is recommended by the European Respiratory Society (ERS).

■ In order to perform the conversions between the two units, mL CO/min/mmHg is multiplied by 0.3348 while mmol/min/kPa is multiplied by 2.987.

In the traditional system, considering all of the above the DLCO adjusted formulas are:

■ For males aged ≥15 years:

Adjusted DLCO (DLCOc) = Predicted DLCO x ((1.7 x Hgb) / (10.22 + Hgb))

■ For children aged <15 years and females regardless of age:

Adjusted DLCO (DLCOc) = Predicted DLCO x ((1.7 x Hgb) / (9.38 + Hgb))

The adjustement of DLCO due to hemoglobin can sometimes be of essential importance given that slight changes in hemoglobin (binding with CO – carbon monoxide) concentration can affect the CO transfer.

In practice, the two values are then compared with reference tables.

Normal hemoglobin values range between 12 – 16 g/dL in women and 14 – 18 g/dL in men and the Hgb test is usually comprised in the CBC – complete blood count.

The diffusing capacity of the lungs for carbon monoxide (DLCO) is a pulmonary function testing, implemented since the early 20^th Century, that tries to evaluate how much oxygen is exchanged between the alveoli (the lung air sacks) and the blood stream at the capillary level. Often, the test is also called TLCO given that instead of diffusing, the term transfer is used.

It basically measures the partial pressure difference between inspired and expired carbon monoxide, therefore looking at how hemoglobin on the erythrocytes (the red blood cells) stocks up on CO.

Factors that are affecting the test and diffusion in the lungs include the atmospheric pressure and other specific patient factors, such as hemoglobin, carboxyhemoglobin, age and sex, which are to be assessed individually as per recommendations from the American Thoracic Society.

DLCO interpretation

The values obtained from the actual pulmonary test are compared to standard table values for a person of same height, age and gender. DLCO corrected normal values are referred to as the DLCO/VA and are considered to be 80% or more of the predicted value.

DLCO is used as measure of lung disease severity and values lower than normal, situated in the Lower Limit of Normal (LLN) might indicate a functional impairment of the alveolar surface area:

■ Restrictive lung disease;

■ Chronic obstructive pulmonary disease (COPD);

■ Emphysema;

■ Pulmonary embolism;

■ Pulmonary hypertension;

■ Cardiac insufficiency or chronic heart failure;

■ Certain cases of anemia.

Increased DLCO results on the other hand may be caused by the following:

■ Polycythaemia;

■ Increased pulmonary blood volume;

■ Left to right intracardiac shunting;

■ Asthma;

■ Hemorrhage.

Pulmonary functions tests PFTs

These are a group of tests, often known as spirometry, that evaluate how well the respiratory system works, specifically the lungs. These are recommended as part of physicals, as part of diagnosis methods in case the patient presents serious respiratory symptoms or in order to monitor different lung diseases such as dyspnea, lung fibrosis or asthma.

The most common parameters measured are listed below:

■ Vital capacity (VC);

■ Forced vital capacity (FVC) –  the volume of air that can forcibly be blown out after full inspiration;

■ Forced expiratory flow (FEF) – measures the speed or air in the middle portion of a forced expiration;

■ The FEV1/FVC ratio – which in healthy adults should between 70 – 85%;

■ Maximal voluntary ventilation (MVV) – the maximum amount of air inspired and expired in a minute;

■ Tidal volume (TV) – the amount of air inhaled and exhaled normally at rest;

■ Total lung capacity – the volume of air present in the lungs.

References

1) Macintyre N, Crapo RO, Viegi G, et al. (2005) Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J; 26(4):720-35.

2) Rosenberg E. (1996) The 1995 update of recommendations for a standard technique for measuring the single-breath carbon monoxide diffusing capacity (transfer factor). Am J Respir Crit Care Med; 154(1):265-6.

3) Hughes JM, Bates DV. (2003) Historical review: the carbon monoxide diffusing capacity (DLCO) and its membrane (DM) and red cell (Theta.Vc) components. Respir Physiol Neurobiol; 138(2-3):115-42.

4) Marrades RM, Diaz O, Roca J, Campistol JM, Torregrosa JV, Barberà JA, Cobos A, Félez MA, Rodriguez-Roisin R. (1997) Adjustment of DLCO for hemoglobin concentration. Am J Respir Crit Care Med; 155(1):236-41.

5) Hegewald MJ, Crapo RO. Pulmonary function testing. In: Mason RJ, Broaddus VC, Martin TR, et al., eds. Murray and Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa: Elsevier Saunders; 2010:chap 24.