What is the most likely diagnosis for a 26-year-old Asian lady with low plasma calcium and elevated ALP?

The most likely diagnosis for a 26-year-old Asian lady with low plasma calcium and elevated alkaline phosphatase (ALP) is osteomalacia.

Osteomalacia is a condition characterized by the softening of bones due to a deficiency of vitamin D, calcium, or phosphate, leading to poor bone mineralization. The key indicators in this scenario are the low plasma calcium levels and elevated ALP. Low calcium levels suggest insufficient mineralization of the bone matrix, while elevated ALP is a marker of increased bone turnover, which occurs when the body tries to compensate for the poorly mineralized bone.

In the context of a young woman, particularly in certain populations, dietary deficiencies or absorption issues related to vitamin D can be common causes of osteomalacia. This condition can lead to symptoms such as bone pain and an increased risk of fractures.

Other conditions, such as osteoporosis, which typically manifests with low bone density but not necessarily with elevated ALP or low calcium in a young adult, would not match these lab findings. Rickets is a similar condition but primarily occurs in children, while Paget's disease of bone generally involves abnormal bone remodeling in older adults and is characterized by increased ALP but usually not low calcium levels.