Role of Extracellular Deposits and Crystals in Diagnostic Pathology: A Case Series and Practical Diagnostic Algorithm

Extracellular deposits (ECDs) and crystals on peripheral blood smears and tissue sections provide valuable diagnostic clues but are often overlooked or misinterpreted. This case series demonstrates the broad spectrum of extracellular materials encountered in routine pathology, ranging from preanalytical artifacts (fibrin strands and lipemia) to clinically significant pathologies (crystalglobulinemia, cryoglobulinemia, and Charcot–Leyden crystals). Each case illustrates how these findings influence diagnostic workup, guide focused laboratory investigations, and affect clinical management. We describe simple bench-side methods, including temperature testing, alternate anticoagulants, and warm handling protocols that aid in differentiating artifacts from disease-associated deposits. A practical, stepwise diagnostic algorithm is proposed to facilitate systematic evaluation, particularly in settings with variable laboratory resources. Recognizing ECDs during routine smear and tissue review improves diagnostic accuracy and expedites appropriate patient management.