Circulating miR-21 as a Potential Diagnostic Biomarker in Symptomatic Giardia lamblia Infection in Tikrit, Iraq

Giardia lamblia is one of the predominant intestinal protozoans and is primarily responsible for global diarrheal illness, especially in areas with scarce sanitation. Conventional diagnostic measures are not highly sensitive and so non-invasive biomarkers are indispensable. In this respect, circulating microRNAs, the miR-21 molecule (especially miR-21-5p), could act as signal waves of host immune response to infection. In the current study, we aimed at investigating an expression of circulating miR-21-5p in patients with symptomatic Giardia lamblia infection and considering its diagnostics. Case–control study of Tikrit General Hospital, Iraq, January–November 2025. A microscopically confirmed sample consisting of 44 giardiasis cases was included, and 40 healthy control participants were also included. Direct microscopy and concentration methodologies were performed for stool samples. Plasma miRNA was extracted and quantitated to calculate by qRT-PCR assay using U6 as internal control. Relative ratios of expressions were determined by the 2^-ΔΔCt method. Statistical analysis employed student t-test and ROC curve. Circulating miR-21-5p expression increased significantly in patients relative to controls (p < 0.001) with a fold change 6.38. The ROC analysis showed remarkable diagnostic performance, AUC of 0.90; sensitivity of 94%, specificity of 90%. Strong correlation between miR-21 expression and ELISA (r = 0.72, p < 0.001) and inverse with PCR Ct (r = −0.78, p < 0.001). Circulating miR-21-5p is markedly enriched in giardiasis and is an excellent candidate as a non-invasive diagnostic biomarker.