Anomalous response of macroamylase to assay temperature.

Macroamylasemia results from the complexing of serum a-amylase (EC 3.2.1.1;a-1,4-glucan 4-glucanohydrolase) to a high-molecular-weight protein or proteins (macroamylase) and is characterized by hyperamylasemia and low urinary amylase clearance, associated with normal renal function. Recently a simplified detection method has been described for macroamylasemia, in which a small column of Sephadex G-100 is used to separate normal unbound amylase from macroamylase (1). Although this technique is a considerable advance on the methods previously used, its use isstilltime consuming and it cannot readily be applied to large numbers of samples. We have investigated the temperature-activity relationships of serum amylase (both at normal and elevated activities) and of macroamylase. These studies suggest that the ratio of amylase activities at two different temperatures can be used to differentiate a case of macroamylasemia from other causes of hyperamylasemia (2). A high serum amylase activity generally means that the urinary amylase-creatinine ratio or amylase clearance must be determined as a preliminary to diagnosing macroamylasemia. The temperature-activity ratio that we describe can be applied directly to a hyperamylasemic blood sample without requiring a sample of urine, and it would therefore seem to be ideally suited to population screening, if our findings are confirmed by other investigators.