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Sample

  1. It is done on the Serum of the patient.
  2. Fasting sample is a better choice.
  3. This test can be done on the random sample as well.
    • How to get good serum: Take 3 to 5 ml of blood in the disposable syringe or in vacutainer. Keep the syringe for 15 to 30 minutes at 37 C and then centrifuge for 2 to 4 minutes to get clear serum.
  4. Keep the sample refrigerated as soon as you separate the serum.
  5. Serum at 0 to 4 °C is stable for 2 to 3 days and at -25 °C is for one month.
  6. Perform the test as soon as possible because ALP activity increases 3 to 10% on standing at 25° C or 4 ° C for several hours.

Precautions

  1. Storage At room temperature increases the ALP activity.
  2. Avoid EDTA and oxalate anticoagulant which decreases Alkaline phosphatase activity.
  3. If serum left at room temperature:
    • Then there is a 1% increase in 6 hours.
    • 3 to 6% in 1 to 4 days.
    • Even may see an increase if refrigerated the serum which is 2%/day.
  4. Recent intake of the food may increase the value.
    1. Values may be 25% higher after taking the high-fat meal.
  5. Drugs like allopurinol, antibiotics, colchicine, indomethacin, fluorides, isoniazid (INH), methotrexate, nicotinic acid, methyldopa, phenothiazine, and probenecid can increase the alkaline phosphatase level.
  6. Drugs like arsenal, cyanides, nitrofurantoin, and zinc salts may decrease the alkaline phosphatase level.
  7. Hemolysis may cause a slight increase in the ALP. ALP is 6 times more in the RBC than the serum.

Indications

  1. Alkaline phosphatase is estimated to detect diseases of liver and bone.
  2. Alkaline phosphatase is the best marker for obstructive jaundice.
  3. Alkaline phosphatase is the marker:
    1. For hepatic metastasis.
    2. In parathyroid diseases.
    3. Vitamin D deficiency.
    4. Acute pain in the abdomen.

Pathophysiology

  1. ALP is found in many tissues, at or in the cell membrane.
    1. ALP is a nonspecific enzyme, capable of reacting with many different substrates.
    2. The highest concentration is found in the liver. Within the liver, ALP is present in the Kupffer cells and these cells line the biliary collecting system. From there this enzyme is excreted in the bile.
    3. ALP is mainly from the liver, biliary tree, nearly up to 50% from the skeleton (osteoblastic cells), a small amount from the intestinal epithelium, renal tubule cells and lower concentration in leucocytes and placenta.
      1. This ALP is age dependent.
    4. ALP (serum)  is denatured at 56 °C and stable at lower temperature.
      1. Liver isoenzyme is moderately heat stable at 55° C but bone isoenzyme is heat labile.
      2. Placental isoenzyme is stable at 65 °C  but not others.
    5. Alkaline phosphatase is called Alkaline because its function is seen between a pH of 9 to 10 and best at a pH of 9.0.
    6. ALP enzymes require Magnesium for the reaction.
  2. Alkaline phosphatase is produced by the bone, bile ducts, intestine, and placenta.

  1. Post-puberty ALP is mainly from the liver.
  2. This is an enzyme present in the blood and its subtypes are present in the liver, intestine bones and placenta.
  3. The conditions which will stimulate bone cells leads to an increase in the level of ALP.

  1. The liver ALP is increased in biliary obstruction when its excretion is impaired.  While in intrahepatic obstruction there is less increased in ALP level as compared to biliary obstruction.
  2. ALP is involved in bone calcification.
    1. The stimulus which increases bone activity cause increase in the ALP level. So elevated level indicate liver or bone diseases.
    2. Bone alkaline phosphatase is produced by osteoblast of the bone and not from the osteoclasts.
    3. ALP level rises during active bone formation like in infants, children, and adolescents. So They have raised the level up to 3 times of the normal than the adults.
    4. Bone alkaline phosphatase indicates bone forming activity.
  3. Pregnancy can also lead to a raised level.
  4. Alkaline phosphatase in urine is from the renal tubule and not from the plasma.
    1. This may be seen in renal lesions as a malignant tumor (carcinoma), nephrosis, nephritis, infarction, and systemic lupus erythematosus.
Alkaline Phosphatase Isoenzymes are:
  1. Liver ALP isoenzyme. This fraction moves fastest on electrophoresis, followed by bone, placenta, and an intestinal fraction.
  2. Bone ALP isoenzyme. This increases due to osteoblastic activity and normally elevated in children and older people above 50 years of age.
  3. Intestinal ALP isoenzyme. this depends upon blood group and secretor status of people. Blood group B or O and secretor are more likely to have this isoenzyme.
  4. Placental ALP.

Basis for classification Isoenzyme liver Isoenzyme intestine Isoenzyme bone Isoenzyme placenta Other isoenzymes
Heat stability Stable at 56 °C for 30 minutes Disappear at 56 °C within 15 minutes Disappear at 56 °C within 10 minutes Stable at 65 °C for 30 minutes Regan isoenzyme more stable
Chemical inhibition  By urea but low by L-phenylalanine   Strong by L-phenylalanine  Strong by urea  but low by L-phenylalanine  Resistance to urea  but strong inhibition by L-phenylalanine  Regan strong inhibition by L-phenylalanine
 Electrophoresis  Most anodic Cathodic to the bone fraction   Intermediate  Migrate with the placenta or bone fraction  Renal isoenzyme more cathodic
Adult Male 25 to 100 U/L
Adult Female 25 to 100 U/L
Children <2 years  = 85 to 235 U/L
  2 to 8 years  = 65 to 210 U/L
  9 to 15 years =  60 to 300 U/L
  16 to 21 years = 30 to 200 U/L 
  1. In the absence of bone disease or pregnancy, markedly raised the level of Alkaline phosphatase ( around 10 times ) is the best marker of liver obstructive pathology like gallstones obstructing the biliary tract.
  1.  1 to 2 times raised level may be seen in various liver parenchymal diseases like Hepatitis and Cirrhosis.
    1. In extrahepatic obstruction due to stones of cancer, ALP increases 3 times the normal.
    2. In case of complete obstruction, ALP may be raised to 10  to 12 times.
    3. In the case of intrahepatic obstruction ALP rises but less than extrahepatic obstruction.
    4. In the case of infectious diseases, ALP rises but <3 times.
    5. In pregnancy, the average increase in ALP is 1.5 times the normal limit between 16 to 20 weeks and it persists till the labor.
      1. After labor ALP comes to normal within 3 to 6 days.
      2. This may be raised in pregnancy complications like hypertension, Eclampsia, and pre-eclampsia, as well as threatened abortion.
  1. Its level may be mildly raised in:
    1. metastatic diseases of the liver.
    2. Hepatocellular carcinoma.
    3. Biliary Cirrhosis.
    4. Intrahepatic and extrahepatic cholestasis.
    5. Gilbert’s syndrome.
    6. Chronic alcohol ingestion.
    7. Diabetes mellitus and diabetic hepatic lipidosis.
  1. Also increased in a bone disease like Paget's disease, healing fractures, Rickets, pregnancy, and childhood.
  2. Metastatic bone tumors.
  3. Osteogenic sarcoma.
  4. Osteomalacia ( while in the osteoporosis ALP is normal ).
  5. There is a higher level of  ALP in children, infant and is 3 times the adult level.
Disease
ALP increased
Explanation
Paget's disease 10 to 25 times Osteoblastic activity increase the ALP 
Osteomalacia Moderate increase Level lowers with treatment
Rickets 2 to 4 times Level lowers with treatment
Osteoporosis Normal level  
Healing fracture  mild raised level  
Fanconi's syndrome Mild to moderate increase  
Primary and secondary hyperparathyroidism mild to moderate increase  
Osteogenic sarcoma Very high level  
Pregnancy third trimester 2 to 3-time increase This is the placental origin
Children  1.5 to 2.5-time increase Growing age 
Metastatic tumor-like Ca prostate raised level  
  1. It is also raised in old age and pregnancy.
  2. Hodgkin’s disease.
  3. Sarcoidosis.
  4. Amyloidosis.
  5. Pulmonary and myocardial infarction.
  6. Hyperthyroidism (with a raised level of calcium).
  7. Chronic renal failure.
  8. Ulcerative colitis.
  9. ALP is increased during the last trimester of pregnancy and falls to normal within 3 to 6 months (postpartum).
  10. Hyperparathyroidism.
  1. Malnutrition.
  2. Hypothyroidism ( Cretinism ).
  3. Milk-alkali syndrome.
  4. Celiac sprue.
  5. Scurvy ( vit.C deficiency ).
  6. Gross anemia.
  7. Deposition of radioactive material in the bone.
  8. In hypophosphatemia.
  9. Pernicious anemia.
  10. Nutritional deficiency of zinc or magnesium.
  1.  If there is no jaundice and there is raised ALP → indicate liver malignancy, drug-induced injury, rarely sarcoidosis and cyst.
  2. ALP presence in the urine indicates renal diseases like renal cell carcinoma, nephrosis, nephritis, SLE, and infarction. 
  3. ALP raised in the third trimester of pregnancy indicates placental origin. 
  4. In osteoclastic activity ALP is normal.
  5. In the osteoblastic activity, ALP is raised.

Possible References Used

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