Radiography is an essential tool in the diagnosis of ARDS. As you asked about clinical chemistries and lab testing, here is a comprehensive answer from the McGraw Hill textbook Fishman's Pulmonary Diseases and Disorders, 5th edition by Grippi et al.

Laboratory Studies

Although no laboratory test is specific for the diagnosis of ARDS, arterial blood gas analysis is essential for confirming the diagnosis.9 PaO2/FiO2 is markedly abnormal in patients with ARDS (Tables 141-1A and 141-1B). In addition to the profound oxygen therapy–resistant hypoxemia that is the hallmark of ARDS, acute respiratory alkalosis may also occur in the early stage. If a patient with ARDS then develops respiratory muscle fatigue, hypercapnia results. In late-stage ARDS, patients typically have increased minute ventilation requirements due to an increasing dead-space fraction, despite possible improvement in oxygen exchange.

In addition to arterial blood gas measurements, several other laboratory studies may be helpful in investigating other causes of respiratory failure and evaluating additional aspects of critical illness associated with ARDS. For example, cardiac enzymes (creatine phosphokinase and troponins) are useful for evaluating the presence of myocardial infarction or cardiac ischemia in patients at risk because of increased age or other factors. The results should be interpreted in conjunction with electrocardiographic findings, since elevations in cardiac enzymes, especially troponins, have been reported in patients with sepsis or septic shock in the absence of coronary artery disease.79,80

Another cardiac-related laboratory test that may be useful in this clinical context is plasma brain natriuretic peptide (BNP), which is secreted by the cardiac ventricles, and, to a lesser extent, the atria. BNP measurements are often utilized in the evaluation of acute shortness of breath in patients presenting to an emergency department.81 In this group, a BNP greater than 500 pg/mL indicates that CHF is likely with a positive predictive value greater than 90%. In the same group, a BNP less than 100 pg/mL suggests that congestive heart is unlikely with a negative predictive value greater than 90%. However, interpretation of an elevated BNP in patients who are critically ill is problematic. Reports indicate that BNP increases with renal failure, and that elevations of BNP greater than 500 pg/mL may occur in patients with sepsis and normal left ventricular function.82 Nonetheless, one can reasonably exclude a cardiac cause for acute pulmonary edema in patients in the intensive care unit if BNP is less than 100 pg/mL.