Chapter VI Select Organ Function Blood TestsLiver Function Tests (LFTs) The following set of tests is commonly used to diagnose liver disease. Almost all types of liver disease can be isolated by the use of these following tests. Liver disease is fairly common today, so these tests are of particular significance in the diagnosing of these related diseases. Test: BSP Bromsulphalein Test This is a liver function test used to diagnose general liver dysfunction, including obstructive liver disease. Clinical Implications: This test uses an injected dye, BSP, for diagnosis of liver disease. After the injection, several blood samples are taken to determine the blood level of the dye. These levels will indicate the liver’s ability to excrete the dye and thus the general functioning of the liver. This test is very diagnostic of inactive cirrhosis of the liver. Test: Serum Bilirubin This test is a measure of the bilirubin in the blood. Normal Value: Total bilirubin – less than 1.5 mg/100ml Clinical Implications: Bilirubin is present in blood at all times due to the breakdown of hemoglobin which occurs all the time. Normally, bilirubin is removed from the blood by the liver. Increased serum bilirubin levels indicate obstructive disease of the liver, hemolysis or actual liver cell damage. Direct bilirubin – quick, one-minute test for bilirubin (usually not accurate) Test: Alkaline Phosphatase This is a liver enzyme test. Alkaline phosphatase (ALP) is produced in the liver and bone, it is also derived from the kidney, intestine and placenta. In obstructive biliary disease, there is elevated serum ALP
Clinical Implications: This test is very useful for diagnosing biliary obstruction. Even in mild cases of obstructive disease, this enzyme is elevated. It is not very useful for diagnosing cirrhosis. If a patient has bone disease, this test may be highly inaccurate, as ALP is also found in bone tissue. Test: SGOT, SGPT, LDH Definition: These enzymes are used to help diagnose liver disease (also MI, refer to previous chapter). Clinical Implications: These enzymes can be indicative of liver disease. However, as stated earlier in this text, these enzymes are also found in other body tissues such as bone, heart, kidney, etc. Isoenzyme tests usually must be performed in order to isolate the isoenzyme that is elevated and if the source is the liver. SGPT – Serum Glutamic Pyruvic Transaminase Normal: 5 – 35 U/ml (highest levels seen in liver disease) SGOT – Serum Glutamic Oxaloacetic Transaminase Test: Blood Ammonia Level of ammonia in the plasma Normal Values:
Clinical Implications: Ammonia is formed due to bacterial action in the intestines and by normal metabolism in all body tissues. Most of this ammonia is then absorbed by the intestines and goes into the portal circulation, where normally the liver converts it to urea and it is excreted by the kidneys. This test then, is most useful in diagnosing hepatic failure, although plasma ammonia levels are not elevated in all cases. Reduced portal circulation (through the liver) can also result in very high ammonia levels. CHF and/or acidosis may also cause a temporary rise in plasma ammonia. Arterial or venous blood may be used for the specimen in most hospitals; some also recommend putting the specimen on ice and transport to the lab. A green-top tube (heparinized) is usually used. NPO, except for water, 8 hours prior to the test is usually recommended. High or low protein diets may also affect the lab test results. Exercise and certain antibiotics (neomycin and tetracycline) will usually affect the test results. Thyroid Function Tests Introduction As most nurses now, the thyroid affects the following in our bodies:
The two main hormones the thyroid secretes are responsible for the stimulation effects throughout the body. They are:
T3 is the stronger of the two hormones. It has a stronger and more rapid metabolic action than T4. Most of the T3 is made of T4 which has been broken down at a cellular level. Some T3 is actually made in the thyroid gland, but most is from the degradation of T4 in the cells. The following tests are the most common ones performed today in most hospitals. Always remember that each hospital is different and the procedure from one place to another will vary. Always consult the lab manual or procedure manual at your facility to be sure that the nursing responsibilities have been carried out properly. Test: BMR Basal Metabolism Rate Normal Values: +5% probably means slight overactive thyroid Clinical Implications: This test is rapidly being replaced today by more sophisticated tests of thyroid function. The test is indirect, meaning that it actually measures oxygen consumption in the body. This oxygen consumption could be directly related to metabolism, as the thyroid hormones affect the metabolic rate. As you see, this test is unreliable, but it is still used occasionally as a general indicator of thyroid function. The patient should be prepared for this. Inform them that they will be asked to breathe oxygen through a set of tubes for a few minutes. The patient should be as “stable” as possible, meaning that he should be free from stress and have no excessive physical activity for 6-8 hours before the test. If it is an outpatient, he should be instructed to sleep at least 8 hours the night before the test and will be asked to lie down for 30 minutes immediately before the test. In the lab were the testing is conducted, room air pressure and temperature are measured. Patient data are collected; height, weight, age and normal sleeping and eating habits must be recorded, as any of these can affect the test. The patient is kept NPO before the test, no smoking is allowed, NPO at home after 9:00 p.m. the night before. The results of the test are recorded as a “plus” or “minus” from the normal, in a percentage. Test: PBI Protein Bound Iodine Measures the amount of iodine in serum Normal Values: 5 – 8 ug (micrograms)/100 ml serum Clinical Implications: In the blood, iodine is not a free molecule, but rather it is bound to protein. Since iodine is stored in the thyroid and used to synthesize thyroxine, the amount of iodine in the serum can give a good indication of thyroid function. Since there is a direct relationship between PBI concentration and the activity of the thyroid, this test is valuable for testing general activity of the thyroid. A low concentration of PBI in blood, indicates hypothyroidism; and a high concentration will usually indicate hyperthyroidism. Test: Radioactive Iodine Uptake (RAI) (RAIU) (uses I 131) Clinical Implications: This is a test of thyroid function. The patient is given a dose of iodine (radioactive iodine), and after a certain length of time, the amounts of the material absorbed are measured. The iodine causes no discomfort for the patient, it is certainly not dangerous to the staff, and the patient can eat soon after the material is ingested. Basic procedure at most facilities:
Levels of radioactive iodine are usually checked, in the blood, in the urine, and in the thyroid itself. As the thyroid gland takes up the iodine, some iodine will be concentrated in the thyroid itself and in the blood. It is the blood concentrations that are measured. It is an indirect measure of how much the thyroid has absorbed. Test: Thyroidal Iodide Clearance This test measures the amount of iodine cleared by the blood in a period of time. Normal Values: 25 ml/min (25 ml plasma is cleared of iodine per minute) Hyperthyroidism 250 ml/min The patient is given an intravenous injection of radioactive iodine. Blood samples are then taken frequently for 1 to 2 hours after the injection. Amounts of iodine are measured and compared to normal. Test: Radioactive Iodine Excretion Definition: Similar to above test, this procedure measures the amount of radioactive iodine excreted in the urine after a test dose is administered. Normal Values: 40 – 80% of dose is excreted in 24 hours Hyperthyroidism less than 40% excreted Test: Thyroid Scan This test is an organ scan of the thyroid (scintillation scanner). Normal Values: Normal concentration of radioactive iodine in thyroid Clinical Implications: Radioactive iodine is injected intravenously. The patient is then scanned by the scintillation camera. The thyroid, of course, absorbs the iodine and the scanner picks it up. If the concentration in the gland is normal, the test is normal. If there are spots on the scan, it may mean tumor growths. The images are recorded on videotape and/or photographs. Test: Triiodothyronine levels (T3 level) Amount of hormone in blood plasma
Clinical Implications: This hormone is one of the thyroid substances. In the blood, it is found in the plasma and in RBC’s. It is strongly attracted to the plasma, therefore, saturating it first. It then goes to the RBC’s. Knowing this, the test for this hormone is performed in the lab by adding a measured amount of radioactive T3 to the patient’s blood sample. If the normal amount of T3 is present naturally, in the blood, the specimen will only uptake a small amount of the radioactive hormone added to the blood. When they measure the amount of the radioactive hormone in the blood, they can deduce that either a normal amount was present in the blood, or that there was too little, or too much. If the thyroid is underactive and not producing sufficient T3, then it follows that when the radioactive T3 is added to the patient’s blood, it will have room to absorb a greater amount. Hypothyroidism less than 11% results (or low T3 results) **Note that hyper- and hypothyroidism will be measured by different criteria (test results); by different experts; always consult your hospital lab for what they consider high and low results. This test is very good for patient safety. No radioactive material is given to the patient, it is added to the blood sample later. No other special preparation is needed, and iodine supplements usually do not affect the results. False high results seen in:
Test: T3 Suppression Test This test is not used very often today; it measures the amount of T3 uptake before and then after patient is given large doses of T3 by mouth. Consult lab for exact procedure on rare occasions this test is ordered. Test: Serum Thyroxine Test (T4 level) This test measures the amounts of thyroxine in the blood. Like Triiodothyronine (T3), thyroxine (T4), is bound to the protein molecules in the blood, and can be influenced by the same things. Test: Pancreatic Enzymes: Amylase Amylase is an enzyme that is synthesized primarily in the pancreas and salivary glands. Anylase (alpha-amylase or AML) helps to digest start and glycogen in the mouth, stomach, and intestine. In cases of suspected acute pancreatic disease, measurement of serum or urine AML is the most important laboratory test. Normal Serum Amylase Results: 25 – 160 U/L **Please note: There are more than 20 different lab methods for determining the results of this test. Be sure to use the normal values at your facility. Be sure to withhold drugs that elevate AML levels such as aspirin, asparaginase, azathioprine, corticosteroids, cyproheptadine, narcotic analgesics, oral contraceptives, rifampin, sulfasalazine, and thiazide or loop diuretics. If they cannot be withheld, note them on the lab slip. After the onset of acute pancreatitis, AML levels begin to rise within 2 hours, peak within 12 to 48 hours, and return to normal within 3 to 4 days. Determination of urine levels should follow normal serum AML results to rule out pancreatitis. Moderate serum elevations may accompany obstruction of the common bile duct, pancreatic duct, ampulla of Vater, pancreatic injury from a perforated peptic ulcer, pancreatic cancer, or acute salivary gland disease. Impaired kidney function may increase serum levels. Test: Pancreatic Enzymes: Lipase Lipase is produced by the pancreas and secreted into the duodenum, where it converts triglycerides and other fats into fatty acids and glycerol. The destruction of pancreatic cells, which occurs in acute pancreatitis, causes large amounts of lipase to be released into the blood. This test is used to measure serum lipase levels. It is most useful when performed with a serum or urine amylase test. Normal values: 56 – 239 U/L (depending on method) Prior to the test, withhold cholinergics, codeine, meperidine, and morphine. If these drugs cannot be withheld, note their use on the lab slip when the specimen is sent to the lab. High lipase levels suggest acute pancreatitis or pancreatic duct obstruction. After an acute attack, levels remain elevated for up to 14 days. Lipase levels may also increase in other pancreatic injuries, such as perforated peptic ulcer with chemical pancreatitis due to gastric juices, and in patient with high intestinal obstruction, pancreatic cancer, or renal disease with impaired excretion. |