Is a pCO2 of 43 mmHg Normal?
Yes, a pCO2 of 43 mmHg is within the normal reference range and does not indicate respiratory dysfunction. 1
Normal Reference Range
The established normal range for arterial carbon dioxide tension (PaCO2) is 34-46 mmHg (4.6-6.1 kPa) in healthy adults, as defined by the American Thoracic Society and international consensus guidelines 1
Your value of 43 mmHg falls comfortably within this range, approximately in the middle of the normal spectrum 1
The 2024 international consensus guidelines similarly define normocapnia as 35-45 mmHg, and your value of 43 mmHg is well within this range 1
Clinical Interpretation
Values are only considered abnormal when they exceed 45-46 mmHg (hypercapnia) or fall below 34-35 mmHg (hypocapnia) 2, 1
Minor variations between laboratories exist but typically remain within 0.2 kPa (approximately 1.5 mmHg) of the standard range 1
PaCO2 should be interpreted in conjunction with pH and bicarbonate levels to fully assess acid-base status, but an isolated value of 43 mmHg requires no further investigation in the absence of symptoms 1
Important Context
A critical caveat: While 43 mmHg is normal in most clinical contexts, interpretation depends on the clinical scenario:
In acute severe asthma exacerbations, a "normal" PaCO2 (like 43 mmHg) in a breathless patient is actually a marker of very severe, life-threatening attack because these patients should be hyperventilating and have low PaCO2 1
In patients with interstitial lung disease or pulmonary vascular disease, PaCO2 is typically 30-35 mmHg due to compensatory hyperventilation, so 43 mmHg might represent relative hypoventilation in these specific populations 1
In COPD patients, PaCO2 is typically elevated (45-55 mmHg), so 43 mmHg would represent good respiratory compensation 1
For a healthy individual or most clinical scenarios, 43 mmHg represents normal ventilatory function and requires no intervention.