Heparin-Induced Thrombocytopenia (HIT) is a prothrombotic and potentially fatal immune complication of heparin therapy. HIT is challenging to diagnose, particularly in critically ill patients where multiple causes of thrombocytopenia must be considered. Diagnostic algorithms for HIT begin with a clinical assessment, followed by laboratory testing when indicated. If Platelet Factor-4 (PF4)/heparin immunoassay and Serotonin Release Assays (SRA) are negative, HIT is deemed unlikely and heparin therapy may be resumed. Current recommendations have excluded the next step in work up for thrombocytopenia after immunoassay and functional assays result negative despite worsening thrombocytopenia following heparin re-initiation. We present the case of an 85-year-old male with multiple comorbidities, found to have a clinical course consistent with HIT despite negative serologic and functional assay results. Our case highlights the challenge in diagnosing heparin-induced thrombocytopenia in a medically complex patient and demonstrates the need for standardized recommendations following negative laboratory results despite high clinical suspicion.