Amylase is involved in the digestion of carbohydrates. It hydrolyzes alpha-1,4-glycoside bonds in polysaccharides, and forms maltose and oligosaccharides. In a healthy adult, the pancreas (40–45%) and salivary glands (50–55%) account for almost all the alpha-amylase levels. It can be found in two isoenzymes. Pancreatic or p-isoenzyme and non-pancreatic, salivary, or s-isoenzyme forms Fallopian tubes, testes, lungs, thyroid gland, tonsils, mammary glands, and sweat glands secrete a little amount of amylase, mainly s-isoenzyme type. (1) Alpha amylase contains 496 amino acids with a molecular weight of 54 KDa. Amylase metabolism is not well understood, and the kidneys play a major role in the excretion of amylase. (2)
Macroamylasemia is a rare, benign condition with a prevalence of 0.5–1.5% in the general population and 2-5% in the population with hyperamylasemia. It is more common in adult males, but the reason for this is unknown. Macroamylasemia was first described by Wilding in 1964. (3, 4)
Macroamylasemia should be suspected in a patient with a high serum alpha-amylase level without an elevation in the urine alpha-amylase level. Serum amylase proteins bind with other serum proteins like immunoglobulins A( 92%), immunoglobulins G (<30%), and others (<5%), forming macromolecular complexes that weigh more than 400 KDa. Nephrones are unable to secrete these macromolecules into the urine due to their large size, which causes the accumulation of these macromolecules in the serum. (5)
COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2, which manifests mainly with respiratory symptoms. Following entry into the cells, Immunoglobulin A, immunoglobulin M, and immunoglobulin G against the S and N proteins of SARS-CoV-2 develop within 1-2 weeks after the onset of the symptoms. In the early phase, the antigen-specific immunoglobulin A level is higher than the immunoglobulin M level. Specific COVID-19 IgG antibodies rise months after the initial infection and remain elevated for more than a year.(6) The alpha amylase molecule can bind with these immunoglobulins, making a macromolecule, which cause macroamylasemia due to the increased half-life of the amylase due to reduced renal clearance.
Among COVID-19 patients, 1–2% of mild to moderate COVID-19 cases and 17% of severe COVID-19 cases had acutely elevated amylase levels. A USA study reported a prevalence of 0.27% of acute pancreatitis in COVID-19 patients, and 69% of them had idiopathic acute pancreatitis. (7) But macroamylasemia was not reported in a COVID-19 patient previously. In this article, we report a patient without any previous history of abdominal pain or high amylase levels who was managed for a mild COVID-19 infection, found to have a persistently elevated amylase level, and later was diagnosed to have macroamylasemia.