Background - 7S collagen, an N-terminal peptide of type IV collagen, is a primary constituent of the basement membrane. To evaluate whether the serum concentration of 7S collagen reflects the severity of inflammatory lung disease, the serum concentration of 7S collagen was measured in patients with adult respiratory distress syndrome (ARDS) and idiopathic pulmonary fibrosis (IPF). Methods - A radioimmunoassay was used for the measurement of 7S collagen. Gas exchange abnormality was expressed as the arterial oxygen tension (PaO2) divided by the fractional concentration of inspired oxygen (FiO2). Results - The mean (SD) concentration of 7S collagen was 2.7 (0.9) ng/ml in 10 healthy subjects, 5.0 (1.5) ng/ml in 11 patients with IPF, and 14.8 (9.7) ng/ml in 13 patients with ARDS. Significant differences were observed between the patients with ARDS and both healthy subjects and the patients with IPF. In the patients with ARDS serum concentrations of 7S collagen were strongly related to PaO2/FiO2 (r=0.61). Moreover, the mean (SD) serum concentration of 7S collagen in the eight patients with ARDS who died (19.5 (10.2) ng/ml) was considerably higher than that of the five who survived (7.1 (2.1) ng/ml). Conclusion - These results suggest that serum levels of the 7S fragment of type IV collagen may have some prognostic value in ARDS.
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