TABLE 2. Disease severity classification when FEV₁ <LLN [4, 25].

Classification	% of predicted	z-score
Mild	≥70	≥−2
Moderate	60–69	−2 to −2.5
Moderately severe	50–59	<−2.5 to −3
Severe	35–49	<−3 to −4
Very severe	<35	<−4

Note: FEV₁, forced expiratory volume in the first second; LLN, lower limit of normal.