Sirolimus has been widely used to treat vascular anomalies in recent years. Routine therapeutic drug monitoring for sirolimus is required to ensure efficacy and prevent adverse effects, due to its narrow therapeutic window and large intra- and inter-individual variability in pharmacokinetics. This article reviewed the analytical methods for sirolimus blood concentration and the comparison studies between different assays, and the target blood concentration range of sirolimus in vascular anomalies was discussed. The analytical methods for determination of sirolimus include immunoassays and liquid chromatography-based methods. Immunoassays exhibit significant positive bias compared to chromatography. Liquid chromatography tandem mass spectrometry is regarded as the “gold standard” in most clinical labs. Generally, goal sirolimus blood concentrations maintain at 5–15 ng/mL or 10–15 ng/mL. However, there are several classifications of vascular anomalies. The treatment of sirolimus in this disease area is complicated, and no guidelines for the implementation of therapeutic drug monitoring could be adhered. Further researches are needed to obtain more high-level evidence-based medical evidence to guidance the therapeutic monitoring and individualized medication of sirolimus.