High TIBC 

A high TIBC level typically indicates that the body has low iron stores, as seen in iron deficiency anaemia.
Iron deficiency occurs when iron levels fall due to blood loss, pregnancy or inadequate intake, leading to symptoms such as fatigue and low haemoglobin. TIBC increases because the body produces more transferrin to try to capture and transport more iron. 

Low TIBC 

A low TIBC suggests reduced capacity to bind iron, often due to iron overload or chronic disease.
High iron levels can occur in conditions such as haemochromatosis, liver disease, or excessive iron intake, and blood tests are used to check iron overload by measuring transferrin saturation and ferritin. In this context, TIBC tends to be low because transferrin is already saturated with iron.