Bone-related disorders: Isolated elevated alkaline phosphatase (alk phos) with normal gamma-glutamyl transferase (GGT) often points towards bone-related conditions. This is because alk phos is an enzyme found in high concentrations in bone tissue. Conditions such as osteomalacia, Paget's disease, or bone metastases can cause elevated alk phos levels without affecting GGT, which is more specific to liver and biliary diseases.

Pregnancy: During pregnancy, especially in the third trimester, alk phos levels can rise due to the production of placental alkaline phosphatase. This is a normal physiological change and does not necessarily indicate pathology.
Vitamin D deficiency: Vitamin D deficiency can lead to increased bone turnover, which may result in elevated alk phos levels. This condition is more common in individuals with limited sun exposure, inadequate dietary intake, or malabsorption.
Hyperparathyroidism: Primary hyperparathyroidism can cause an increase in alk phos due to the increased bone resorption stimulated by elevated parathyroid hormone levels.

Bone metastases: Although less common, it is crucial not to miss the diagnosis of bone metastases, especially in patients with a known history of cancer. Elevated alk phos can be an indicator of bone involvement.
Osteosarcoma: A rare but critical diagnosis, osteosarcoma (bone cancer) can present with elevated alk phos levels. Early detection is vital for treatment outcomes.

Hypophosphatasia: A rare genetic disorder characterized by deficient activity of tissue-nonspecific alkaline phosphatase, leading to elevated levels of certain substrates and low alk phos activity in some forms, but can present with elevated alk phos in other forms, particularly in adults.
Wilson's Disease: Although primarily associated with liver disease and elevated GGT, some cases of Wilson's disease can present with isolated elevated alk phos, especially if the liver disease is minimal or in the early stages.