The Vitamin Biotin Kit is a microtiter plate test kit based on a microbiological assay which measures the total biotin content in serum. Serum samples are diluted and added into the microtiter plate wells coated with Lactobacillus plantarum which metabolizes biotin. The presence of biotin both in standards and samples gives a biotin-dependent growth response. After incubation at 37 °C for 48 hr, the growth of Lactobacillus plantarum is measured turbidimetrically at 610 - 630 nm (alternative at 540 - 550 nm) in an ELISA-reader. A dose response curve of absorbance unit (optical density, OD at 610 nm) vs. concentration is generated using the values obtained from standard. Biotin present in the samples is determined directly from this curve.