"Isolated" elevation of alkaline phosphatase: significance in hospitalized patients.

The significance of alkaline phosphatase (AP) elevation with otherwise normal transaminase and bilirubin values remains unclear. We evaluated the clinical outcome of hospitalized patients with an "isolated" AP elevation. Eighty-seven inpatients with isolated AP elevation were identified during February 1984 and followed for 1 year. Forty-five of 87 patients had normalization of AP during the follow-up period, usually within 1-3 months. The most common diagnoses in this group were congestive heart failure in nine, benign bone disease in six, and treatable malignancy in three patients. Twelve patients had no apparent explanation for the transient rise of AP. Persistent AP elevations were noted in 42 patients--14 of whom had terminal malignancies. Clinically obvious life-threatening diagnoses were made in 24 of the patients with persistent AP elevation. The etiology of AP elevation remained enigmatic in seven patients: two died, four are stable during 1 1/2-3 years of follow-up, and one patient was found to have metastatic carcinoma 17 months later. If the initial AP was greater than 1 1/2 times normal, there was a higher likelihood of persistent elevation (68% vs. 41%, p less than 0.05). Isolated elevations of AP in inpatients may be associated with a variety of medical illnesses and often normalize within months. If the AP elevation is persistent, there is usually a clinically obvious diagnosis. A reasonable approach to such patients is a careful history, physical exam, and routine lab studies to detect obvious diagnoses, followed by repeat enzyme determination at 1-3 months.