Serum Uric Acid/Serum Creatinine Inversely Related to Some Lung Function Measures

The ratio of serum uric acid to serum creatinine (SUA/SCr) is inversely related to 2 important lung function parameters — forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV₁); however, the SUA/Scr is not associated with the FEV₁/FVC ratio, according to study findings published in BMJ Open Respiratory Research.

Serum creatinine and SUA are both common biomarkers of renal function, and SUA is known to reflect hypoxia status. Moreover, the SUA/SCr ratio is related to the progression of obstructive sleep apnea, chronic obstructive pulmonary disease, chronic respiratory failure, and hypertension. In the current study, investigators sought to ascertain the relationship between the serum uric acid/serum creatinine (SUA/SCr) ratio and lung function in the general US adult population and to gain insight into the role of SUA/SCr in pointing to early lung function abnormalities.

The investigators used data from the National Health and Nutrition Examination Survey (NHANES), conducted by the Centers for Disease Control and Prevention, which collects US population data on nationwide health and nutritional status every 2 years. The researchers conducted a cross-sectional study evaluating 3 (2-year) data cycles from 2007 through 2012. The analysis involved data from 9569 adults (average [SD] age, 42.53 [6.17] years) who were primarily White and non-Hispanic, regarding diet, personal life history, medical examination, demographics, comorbidities and laboratory results. The link between the SUA/SCr ratio and lung function was evaluated with a regression model, generalized linear model, 2-piecewise linear regression model, and XGBoost algorithm model.

Participants with higher SUA/SCr ratio vs lower SUA/SCr ratio were more likely to be young, White/non-Hispanic, female, and married; they were also more likely to be without respiratory disease and to have hypertension, diabetes, a lower level of physical activity, higher BMI, higher education, lower poverty to income ratio, and a higher alcohol consumption level.

In the fully adjusted model, the researchers found that FEV₁ decreased by 36.956 and FVC decreased by 47.630 for each additional unit of SUA/SCr ratio. No association was found between FEV₁/FVC and SUA/SCr (ie, the association was positive but without statistical significance).

In the XGBoost model of FVC, the most important blood markers affecting lung function parameters were glycohemoglobin, total bilirubin, SUA/SCr, total cholesterol, and aspartate aminotransferase. In the XGBoost model of FEV₁, the most important blood markers affecting lung function parameters were glycohemoglobin, total bilirubin, total cholesterol, SUA/SCr, and serum calcium. Investigators constructed a smooth curve to determine the linear and inverse association between SUA/SCr ratio and FVC or FEV₁.

Study limitations include the cross-sectional study design; unconsidered confounding factors; the inability to establish causality using the NHANES database; the inclusion of patients with respiratory diseases, hypertension, and diabetes; and lack of generalizability beyond the US population.

“Based on NHANES data from 2007 to 2012, we found that the SUA/SCr was inversely associated with lung function parameters (FVC, β=−47.630; FEV₁, β=−36.956) after adjusting for the demographic data, examination data, personal life history data, comorbidities data and laboratory data,” investigators concluded. “In the general American population, the SUA/ SCr ratio is inversely linked with FVC and FEV₁, but not with FEV₁/FVC.”