ALKALINE PHOSPHATASE ELEVATION
ALKALINE PHOSPHATASE ELEVATION: Excerpt from Differential Diagnosis in Primary Care
Developing a list of diagnostic possibilities for an elevated alkaline
phosphatase level involves the use of biochemistry and physiology. As with
other laboratory values, we need to know where alkaline phosphatase is
produced, how it is transported, and how it is degraded or excreted.
Alkaline phosphatase is produced in many tissues but in terms of
pathophysiology, only the osteoblasts of the bone need be recalled. Thus,
disorders that increase osteoblastic activity such as metastatic tumors of
the bone, osteogenic sarcoma, Paget disease, and primary and secondary
hyperparathyroidism may cause the alkaline phosphatase level to increase and
must be considered in the differential. Transport of blood alkaline
phosphatase does not seem to be affected by disease. However, the
excretion of alkaline phosphatase seems to take place in the liver by an
undetermined pathway, but anything that blocks the cholangioles or biliary
tree will usually cause an elevation of alkaline phosphatase. Consequently,
carcinoma of the head of the pancreas, common duct stones, carcinoma of the
ampulla of Vater, and drugs that produce cholestasis (such as
chlorpromazine) may cause an elevated alkaline phosphatase. Metastatic
carcinoma of the liver probably produces an elevated alkaline phosphatase by
blocking individual cholangioles. In addition to the above diagnostic
possibilities, there are disorders that cause an elevated alkaline
phosphatase level by an unknown mechanism such as pregnancy, sepsis, and
gynecologic malignancies that must be included in the differential.
Approach to the Diagnosis
If the elevated alkaline phosphatase level is related to liver disease,
the clinical examination will often show jaundice or hepatomegaly. If it is
related to bone disease, the clinical examination will show bone pain,
pathologic fracture, or bone mass. A liver profile will also help diagnose a
liver disorder, but a CT scan of the abdomen may be necessary. A skeletal
survey will usually reveal bony metastasis and other disorders of the bone,
but a bone scan may be necessary to show early metastasis to the bone. A
serum parathyroid hormone (PTH) level will help diagnose primary
hyperparathyroidism, whereas secondary hyperparathyroidism (rickets, etc.)
will require the specialized tests listed below.
Other Useful Tests
-
CBC
-
Chemistry profile (liver disease)
-
Sedimentation rate (hepatitis)
-
Urinalysis (renal tubular acidosis)
-
24-hour urine calcium (hyperparathyroidism, malignancy)
-
Gallbladder ultrasound (common duct stone)
-
ERCP (obstructive jaundice)
-
Transhepatic cholangiogram (obstructive jaundice)
-
Liver biopsy (cirrhosis, hepatitis)
-
Bone biopsy (metastatic malignancy)
-
d-Xylose absorption test (malabsorption syndrome)
-
Acid phosphatase (metastatic cancer of the prostate)
-
PSA (metastatic cancer of the prostate)
-
Vitamin D metabolites (25-hydroxycholecalciferol) (rickets,
osteomalacia)
-
Exploratory laparotomy
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins MD, FACP
- Year of Publication: 2007
- Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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