Diffusing Capacity Of The Lungs For Carbon Monoxide (DLCO) Calculator

DLCO explained

Changes in haemoglobin impact on the CO transfer, therefore, when testing the diffusing capacity of the lungs for carbon monoxide, in some cases, the test result needs to be corrected for haemoglobin levels.

The variables used by the above DLCO calculator are:

■ Patient age and gender (to be used for correction);

■ Hemoglobin, measured in g/dL;

■ Predicted DLCO, measured in either mL CO/min/mmHg or mmol/min/kPa.

These are input in the following equation:

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

Where the Age & Sex-Factor is 9.38 for females and children and 10.22 for males aged 15 and above.

Therefore, the formulas can be written as:

■ Adjusted DLCO (for children <15 and females) = Predicted DLCO x ((1.7 x Hgb) / (9.38 + Hgb))

■ Adjusted DLCO (for males ≥15 years) = Predicted DLCO x ((1.7 x Hgb) / (10.22 + Hgb))

There are to measurement systems in place for reporting DLCO values:

■ The traditional one (mL CO/min/mmHg) by the American Thoracic Society (ATS), uses the standard temperature and pressure, dry conditions, also known as STPD.

■ The SI one (mmol/min/kPa) is recommended by the European Respiratory Society (ERS).

In order to perform the conversion between the two, mL CO/min/mmHg needs to be multiplied by 0.3348 while mmol/min/kPa needs to be multiplied by 2.987.

The DLCO is a pulmonary function testing that evaluates how much oxygen is exchanged between the alveoli (the lung air sacks) and the blood stream at the capillary level.

The test is also known as TLCO where instead of diffusing it is used the term transfer.

The test itself measures the partial pressure difference between inspired and expired carbon monoxide. This is given by how well hemoglobin on the erythrocytes (the red blood cells) stocks up on CO.

Normal hemoglobin values (obtained during CBC count) range between 12 – 16 g/dL in women and 14 – 18 g/dL in men.

Result interpretation

The DLCO corrected normal values are referred to as the DLCO/VA and are 80% or more of the predicted value.

Values that are lower than normal (Lower Limit of Normal) indicate that there may be a functional impairment of the alveolar surface area, often characteristic of the following:

■ Chronic obstructive pulmonary disease (COPD);

■ Restrictive lung disease;

■ Emphysema;

■ Chronic heart failure;

■ Pulmonary hypertension;

■ Pulmonary embolism;

■ Certain cases of anemia.

On the other hand, greater than normal DLCO results are an indication of:

■ Polycythaemia;

■ Left to right intracardiac shunting;

■ Asthma;

■ Increased pulmonary blood volume;

■ Acute or diffuse.

It is important to note that there may be individual factors that affect the diffusion of CO in the lungs, thus impact on the test result, such as atmospheric pressure, carboxyhemoglobin or patient age and gender.

Pulmonary function tests

PFTs are also known as spirometry and assess the functioning of the respiratory system. This is part of diagnostic methods in patients with serious respiratory symptoms and part of monitoring tests in several lung diseases such as lung fibrosis or asthma.

The following table introduces the most common parameters tested for:

References

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

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

3. Rosenberg E. 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. 1996; 154(1):265-6.

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