Hypoxia, or low oxygen condition, is a normal physiological response to certain body stressors such as high altitudes. Such a condition can result in dizziness, light-headedness, nausea, and related reactions. These reactions may be a result of hypoxic conditions at the system level or the cellular level, or both.

Cellular hypoxia can also be a symptom of pathological conditions and is often used as a marker for tumor cells. Tumor cell hypoxia results from an imbalance between the oxygen supply available and the oxygen consumption of the rapidly dividing cells. Cell hypoxia can result in decreased effectiveness of certain anti-cancer treatments including radiation therapy.

In response to hypoxic conditions, the hypoxia-inducible factor 1 transcriptional activator complex (HIF-1) plays a role in activating several hypoxia-responsive genes such as erythropoietin and VEGF. During hypoxia, the alpha subunit of HIF-1 accumulates and translocates from the cytosol to the nucleus, where it dimerizes with the beta subunit and becomes transcriptionally active. It then binds transcriptional coactivators to induce gene expression.

HIF-1 activity levels can be measured in vitro by way of a DNA binding assay. Traditionally this has been accomplished by an electrophoretic mobility shift assay (EMSA), but this method can take up to 3 days to get results. A more user-friendly method is now available that gives results in about 4-5 hours. The assay uses an antibody-based method and is performed in a standard 96-well microplate.