Alkaline Phosphatase (ALP): Test explanation and increased and decreased level by nursesnote

 Alkaline Phosphatase (ALP)

Normal Findings

Elderly: slightly higher than adult.

Adult:30-120 units/L or  0.5-2.0 ukat/L( Sl units)

Child/ adolescent:

• <2 years: 85-235 units/L
• 2-8 years: 65-210 units/L
• 9-15 years: 60-300 units/L
• 16-21 years: 30-200 units/L

Indications

ALP is used to detect and monitor diseases of the liver or bone.

Test Explanation

Although ALP is found in many tissues, the highest concentrations are found in the liver, biliary tract epithelium, and bone. The intestinal mucosa and placenta also contain ALP. This phosphatase enzyme is called alkaline because its function is increased in an alkaline (pH of 9 to 10 ) environment. This enzyme test is important for detecting liver and bone disorders. Within the liver, ALP is present in Kupffer cells. These cells line the biliary collecting system. This enzyme is excreted into the bile. Enzyme levels of ALP are greatly increased in both extrahepatic and intrahepatic obstructive biliary disease and cirrhosis. Other liver abnormalities, such as hepatic tumors,hepatotoxic drugs, and hepatits, cause smaller elevations in ALP levels. Reports have indicated that the most sensitive test to indicate tumor metastasis to the liver is the ALP.

 Bone is the most frequent extrahepatic source of ALP; new bone growth is associated with elevated ALP levels. Pathogenic new borne growth occurs with osteoblastic metastatic ( eg. breast, prostate) tumors. Paget disease, healing fractures, rheumatoid arthritis, hyperparathyroidism, and normal-growing bones are source of elevated ALP levels as well.

Isoenzymes of ALP are also used to distinguish between liver and bone diseases. These isoenzymes are most easily differentiated by the heat stability test and electrophoresis. This isoenzymes of liver origin (ALP1) is heat stable; the isoenzyme of bone origin (ALP2) is inactivated by heat. The detection of isoenzymes can help differentiate the source of the pathologic condition associated with the elevated total ALP. ALP1 would be expected to be high when liver disease is the source of the elevated total ALP. Another way to separate the source of elevated ALP is to simultaneously test for 5'-nucleotidaes. This later enzyme is made predominantly in the liver. If total ALP and 5'- nucleotidase are concomitantly elevated, the disease is in the liver. If 5'-nucleotidase is normal, the bone is the most probable source. 

Interfering factors

• Recent ingestion of a meal can increase the ALP level.
• Age: young children with bone growth have increased ALP levels. This is most magnified during the growth spurt. Females and males differ in age of growth spurt.
• Drugs that may cause increased ALP levels include albumin made from placental tissue, allopurinol, antibiotics, azathioprine, colchicine, fluorides, indomethacin, isoniazid (INH), methotrexate, methyldopa, nicotinic acid, phenothiazine, probenecid, tetracycline, and verapamil.
• Drugs that may cause decreased levels include arsenical, cyanides, fluorides, nitrofurantoin, oxalates, and zinc salts.

Procedure and patient care

• Fasting: no
• Blood tube commonly used: red
• Note that overnight fasting may be required for isoenzymes. 

Test results and clinical significance 

Increased levels 

• Primary cirrhosis 
• Intrahepatic or extrahepatic biliary obstruction. 
• Primary or metastatic liver tumor : ALP is found in the liver and biliary epithelium. It is normally excreted into the bile. Obstruction, no matter hoe mild, will cause elevations in ALP.
• Metastatic tumor to the bone.
• Healing fracture 
• Hyperparathyroidism
• Osteomalacia
• Paget disease 
• Rheumatoid arthritis 
• Rickets: The ALP comes from the bone in the above-noted disease. 
• Intestinal ischemia or infarction 
• Myocardial infarction 
• Sarcoidosis

Decreased levels

• Hypophosphatemia: There is insufficient phosphate to make ALP.
• Hypophosphatasia 
• Malnutrition 
• Milk-alkali syndrome 
• Pernicious anemia
• Scurvy ( vitamin C deficiency )