Pneumonia: This condition is characterized by inflammation of the lung tissue, often caused by bacterial, viral, or fungal infections. Symptoms such as shortness of breath (sob), desaturation (low oxygen levels), congested cough, and an elevated white blood cell (WBC) count are typical for pneumonia, making it the most likely diagnosis given the combination of these symptoms.

Acute Bronchitis: Although often viral and thus not always presenting with an elevated WBC, acute bronchitis can cause a congested cough and, in severe cases, lead to desaturation. It's less likely than pneumonia to cause significant desaturation but remains a consideration.
Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: Patients with COPD can experience worsening of symptoms such as cough and shortness of breath during an exacerbation, which can be triggered by infection or other factors. An elevated WBC count could be present if there's an infectious component.
Asthma Exacerbation: Severe asthma attacks can lead to significant respiratory distress, including desaturation and a congested cough. While asthma is more commonly associated with eosinophilic inflammation, bacterial infections can also trigger exacerbations and lead to an elevated WBC count.

Pulmonary Embolism (PE): Although PE typically presents with sudden onset of dyspnea and may not always cause a congested cough, it's a critical diagnosis to consider due to its high mortality rate if untreated. Desaturation can occur, and while an elevated WBC is not a hallmark, it can be present, especially if there's associated infection or inflammation.
Sepsis: Sepsis, particularly when originating from a pulmonary source, can present with respiratory symptoms including cough and desaturation, along with a significantly elevated WBC count. It's crucial to identify and treat sepsis promptly due to its high mortality rate.

Cystic Fibrosis Exacerbation: In patients with known cystic fibrosis, an exacerbation can lead to increased respiratory symptoms, including a congested cough and desaturation, along with an elevated WBC count due to infection.
Interstitial Lung Disease (ILD) Exacerbation: Certain ILDs can present with or exacerbate respiratory symptoms, including desaturation and cough. While less common, and the pattern of WBC elevation might differ, considering ILD is important in the appropriate clinical context.
Lymphangitic Carcinomatosis: This rare condition, involving metastatic cancer spreading to the lymphatics of the lung, can cause respiratory symptoms similar to those described, including cough and desaturation. An elevated WBC count might be present due to associated infection or paraneoplastic syndromes.