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an elevated ALKALINE PHOSPHATASE, a serum level greater than 110 IU/L. Body sources of alkaline phosphatase include neo-osteogenesis of bone, intestines, liver, placenta, and white blood cells. Often elevated levels are associated with complications of the liver or gallbladder. A confirmatory test of 5' nucleotidase or gamma glutamyl transferase (GGT) will determine hepatic versus other origins of alkaline phosphatase elevation. In the presence of liver disease, increased levels of alkaline phosphatase will be present with a concomitant rise in the 5' nucleotidase and GGT. Gamma glutamyl transferase is also increased in persons who have recently ingested even minute amounts of alcohol and is therefore a less specific test. Isoenzyme testing is also an option to determine the source of alkaline phosphatase elevation. An elevation of hepatic alkaline phosphatase usually implies impaired biliary tract function with resultant cholestasis, but this elevation also occurs with infiltrative diseases of the liver, masses or abscesses of the liver, primary biliary cirrhosis and primary sclerosing cholangitis. Cholestasis from impaired biliary tract function may result from either intrinsic liver or bile duct disease/malignancies or extrahepatic common bile duct compression usually from tumors of ampulla or pancreatic head.
In cases where alkaline phosphatase elevation is secondary to bone disease, its elevation is a marker of osteoblastic activity. In bony disease, the alkaline phosphatase elevation is usually associated with hypercalcemia. Common bone diseases include metastatic bony lesions, Pagets disease, secondary hyperparathyroidism of renal disease, osteomalacia, rickets, primary hyperparathyroidism, and hyperthyroidism. The exception is multiple myeloma where hypercalcemia is secondary to osteoclastic bone disease and the alkaline phosphatase level is normal. Clinically, pathologic fractures of the sternum are considered pathognomonic of multiple myeloma, and bone pain of the ribs or back that is exacerbated by movement is considered characteristic.
During pregnancy, maternal alkaline phosphatase increases. This is the result of placental alkaline phosphatase production, and the elevation resolves puerperium.
Intestinal isoenzyme is seen most commonly in persons who are blood group O and are secretors of this isoenzyme. Serum levels are also influenced by diet in the above persons. Peak serum levels are seen 2 to 3 hours after a high-fat meal.
The workup of an elevated alkaline phosphatase begins with attempting to determine which organ system is the source of the elevation. Female patients of reproductive age should undergo a pregnancy test. If the 5' nucleotidase or GGT are elevated, a right upper quadrant ultrasound or abdominal CT scan should be obtained to identify choledocholithiasis, infiltrative diseases, abscesses, or mass lesions. If a mass lesion greater than 2 centimeters is identified, a markedly elevated alpha feto-protein (AFP) level is consistent with hepatocellular carcinoma (HCC). Hemangiomas, hepatic adenomas, and metastatic lesions will present with a normal AFP; however, HCC is still a possibility and biopsy may be required. If the mass is in the head of the pancreas then CA 19-9 tumor marker elevation would be indicative of pancreatic cancer, whereas as elevation of the serum IgG or IgG4 would suggest autoimmune pancreatitis. In patients with suspected primary biliary cirrhosis or primary sclerosing cholangitis, serum should be obtained to determine if antimitochondrial antibody is present or an ERCP should be performed, respectively. If the 5' nucleotidase is normal, plain radiographs of areas associated with pain or deformity might detect lytic bone lesions or Pagets disease, respectively. If there are no deformities or painful areas, a bone scan might provide some information. Isolated asymptomatic alkaline phosphatase elevations less than two times normal usually do not warrant work-up as an etiology is often never found or does not change patient management, although determination of the serum 25-hydroxyvitamin D level may reveal underlying vitamin D deficiency as the etiology.