Development and Evaluation of a Lyophilized Plasma-Based Internal Quality Control for Human Immunodeficiency Virus Rapid Diagnostic Tests

<b>Background/Objectives:</b> Rapid diagnostic tests (RDTs) for human immunodeficiency virus (HIV) are widely used, but most kits lack standardized internal quality control (IQC) materials. In this study, we aimed to develop and evaluate a plasma-based IQC compatible with five HIV RDT brands and with proven long-term stability. <b>Methods:</b> Control samples at three reactivity levels were tested with five HIV RDT kits in lyophilized and liquid forms. Lyophilized samples were produced with and without trehalose, whereas liquid samples were prepared with and without StabilZyme™ SELECT Stabilizer (Stabilizer). Accelerated stability testing was performed at 37 °C and 45 °C for 28 days, and the most stable formulation was selected for long-term storage at 4 ± 2 °C and 25 ± 5 °C. Stability was assessed based on test-line visibility and signal intensity. Signal-intensity trends were analyzed using simple linear regression with a <i>t</i>-test on the slope; samples were considered stable when no significant trend was detected (<i>p</i> > 0.05). <b>Results:</b> Reactivity measured using the Elecsys HIV combi PT assay yielded cutoff index (COI) values of 772.65 (1:8) for the strong-positive control and 269.95 (1:25) for the weak-positive control. Trehalose-containing lyophilized samples maintained reactivity under accelerated testing at 37 and 45 °C and for 6 months at 4 ± 2 °C and 25 ± 5 °C, with no significant change in signal intensity (<i>p</i> > 0.05). <b>Conclusions:</b> The plasma-based IQC materials were compatible with all five HIV RDTs, and trehalose-stabilized lyophilized plasma showed high stability, supporting transport and storage without strict cold-chain requirements.