Laboratory Tests Interpretation

Chapter II: Collection Techniques

Collection Considerations

There are many factors to consider when collecting lab specimens; and prior to diagnostic tests. Preparation of the patient prior to the test or diagnostic measure is vitally important to the results of the test. Many laboratory tests and diagnostic tests do not require any extensive preparation. However, the nurse should pay very close attention to those tests that do require preparation.

The type of blood sample needed is very important. The type of blood depends upon the test ordered. Different types of blood samples include Whole Blood, Plasma, Serum, Venous Blood, Capillary, or Arterial Blood.

In most common lab tests, venous blood is used. The lab will then extract serum or plasma, depending upon the test to be performed. Venous blood is a good indicator of the physiological conditions throughout the body. It is also relatively easy to obtain. Therefore, venous blood is used most frequently for testing.

Be sure to collect the specimen in the correct blood tube. Certain blood specimens must be collected in tubes with no anticoagulant. Some specimens must be collected in a tube with anticoagulants. Be sure to handle the specimens correctly. Some blood specimens must be gently mixed with the anticoagulant in the tube. Some blood specimens must not be shaken in the tube.

In addition, the collection procedure itself may cause problems. Hemoconcentration may occur due to prolonged tourniquet constriction. Hemodilution may occur due to drawing the blood sample from the same arm with an intravenous infusion of fluids running. Hemolysis may occur due to rough handling of the sample or from drawing the blood through a small-gauge needle.

Arterial blood samples are necessary for obtaining the blood pH and the levels of dissolved Oxygen and Carbon Dioxide in the blood. Arterial blood sampling will be discussed later in the text in detail. However, it is well known that arterial sampling carries a higher risk to the patient than does venous sampling. Arterial puncturing carries a higher risk of hematoma and arterial spasm and hemorrhage.

Patient Identification:

Probably the most important factors regarding laboratory tests and/or procedures are patient identification and sample identification. The nurse should be very careful to properly identify the patient and the specimens obtained. If the nurse is not going to directly gather the specimen, then the nurse should be sure the lab tech has the correct patient. Be sure that the tech has the correct room number of the patient. Be sure to inform the lab of any changes in room numbers. The lab requisition slip may have a room number that is incorrect because the patient was moved to another room.

This happens very commonly. However, the lab tech is supposed to check the patient’s name band, but we all know that many times they are in a rush and the name bland is not checked carefully. Be sure to check the patient’s wrist band for name and patient admission number. Be sure to accurately label all specimens obtained with the patient’s name, admission number and time obtained. Also be sure to identify the source of the specimen, such as blood, sputum, wound, arterial blood, etc.

Many busy laboratories today, receive a very large number of specimens that are not labeled at all, or are improperly labeled. This places a huge burden on the laboratory and upon the patients. Improperly labeled specimens must be discarded. This means a tremendous waste of time and money for the facility and for the patients. In addition, the patient must have the specimen drawn again. This could lead to delays in treatments.

Every hospital is different in their procedure for handling specimens. However, there are some common factors that should be considered. In the end, always follow the procedure at your hospital. When in doubt about a lab test or diagnostic procedure, consult your laboratory procedure manual or contact the lab or the department responsible for the test. In most cases, they are more than glad to inform you concerning any special considerations needed for a test or procedure.

Quantity of Samples

The amount of the sample needed depends upon many factors. Each lab is different in the amount of blood or other body fluid or tissue required to perform the analysis. Generally speaking, if the blood is run using modern automated analyzers, the amount of blood may be 10 ml or less for each test. If the tests are run individually, or if the tests are complicated, larger quantities of blood may be needed.

The quantity of the sample usually dictates the method of collection or collection procedure. The overall goal is to get the required amount of blood with only one venipuncture. Multiple venipunctures are avoided if possible, even when gathering large amounts of blood. A single glass or disposable plastic needle and syringe may be used to obtain a small sample of 10-20 ml of whole blood. This amount is usually sufficient to perform one or two tests. However, for a series of tests, more blood is needed.

In order to avoid multiple venipunctures, it is usually best to use an evacuated blood tube system such as the “Vacutainer” or “Corvac” collection systems. These systems are very popular for drawing multiple samples of blood. They use blood tubes with a rubber stopper and a vacuum inside the tube. These tubes are manufactured in a variety of sizes and with a variety of additives in the evacuated tubes. Color-coded tubes indicate the different additives in the tube. The vacuum in the tube causes just the correct volume of blood to be drawn into the tube. The tubes are consecutively used to draw blood from one venipuncture site, thereby negating the use of multiple punctures. This, of course, is under ideal conditions. We assume that correct technique is being used. We also assume that the patient’s vein will support multiple samples being drawn at one time from one location. These tubes hold 2-20 ml of blood in each tube.

In infants and children, microanalysis techniques allow sampling of capillary blood through micropipettes or capillary tubes. This technique is used when the patient is an infant/child or has severe burns and/or has absolutely no useable veins to draw from. This technique is time-consuming and very expensive. Therefore, if possible, the multiple-sample technique is preferred. Micropipettes hold from 30 ul to 50 ul of serum or plasma.

Safeguards for veniuncture:

In case of syncope, be sure to place patient in a comfortable but “safe” position. The most common position is sitting or lying down.
If using a needle and syringe to draw blood, be sure not to inject air into the vein. Be sure to have the plunger completely depressed before you start the procedure.
Avoid drawing blood in an extremity used for infusing intravenous solutions. The solutions will dilute the blood directly proximal to the IV site. You may draw blood (below) distal to the IV site, being sure not to draw too close to the IV site. You are too close, if your venipunture activities touch the IV site or interfere with the infusion of the IV in any way. Also be sure not to contaminate the IV site while drawing blood near the site.

Laboratory Requisitions:

The following items should be included on the lab requisition:

Full name: middle name should be included to avoid confusion in the even that there is another patient with the same first and last name.
Location: inpatient, room, unit, outpatient, address.
Patient’s identification number: this identification can be very useful for instance in the blood bank.
Patient age and sex: in evaluating laboratory results, the reference values may differ for age and sex; disease prevalence may be age-or sex-linked.
Name(s) of the physician(s): name all of the physicians on the case, “panic values” should be called to the attention of the physician ordering the test; a physician may have some specific test guidelines for his patients.
Name of the test and the source: reference3 values may be different for the different biologic specimens (e.g., serum and CSF glucose); in microbiology, it is essential to know the source of the swab.
Possible diagnosis: essential for evaluating laboratory results and selecting appropriate methodology; (media selection in microbiology).
The date and time the test is to be done: some tests must be scheduled by the laboratory; blood transfusions may require ample advance notice; patient preparation and diet regulations need to be conserved.
Special notation: provide relevant information to assist the laboratory—e.g., medications taken; for home assay, the point in the menstrual cycle when the specimen was obtained; for microbiology, the patient’s sensitivity to drugs.

Patient’s Diagnosis and Patient’s Condition

It is very important to identify and patient condition or activity that might affect the lab test or diagnostic test being performed. Always be sure to identify anything that might be relevant to that particular test. Now, you might say that this is a very broad statement; and you are very correct. You as the nurse, however, should be alert to conditions that could possibly influence tests. For example, the patient’s temperature can affect certain tests. Some patients are taking supplementary oxygen. Some patients might have just eaten a very large meal.

Of course it is impossible to memorize every single lab test, along with every single factor that might affect these tests. Therefore, it is wise for every nurse to simply make note of any unusual conditions present during the test. For example, your patient has a 24-hour urine test ordered. When you begin the collection of the test, you will note the time in your nurse
‘s notes. Therefore, when you mention that you have started the collection, also mention any other unusual conditions.

You might chart as follows:

11/13 “24-hour urine started at 11:00 a.m. Patient emptied bladder at this time. Patient c/o mild abdominal pain, no abdominal distention noted. Patient is taking iron supplements and multivitamin supplements. Patient also has been on a high protein diet for 2 weeks ordered by Dr. Jones. Patient also has a history of CHF and renal stones. Patient returned from physical therapy at 10:45 a.m. where he stated that he exercised very heavily.”

The above is a detailed description of the patient’s condition at the time the test was started. Perhaps later when the doctor sees the results of the test, he/she might look back and see that the patient was on a high protein diet. A high protein diet might affect the results of the 24-hour urine test. Or, perhaps the heavy exercise might affect the results of a particular test. Therefore, I would say to nurses that you should be very aware and observant when any laboratory tests or diagnostic tests are ordered. Even if you are not familiar with ALL of the tests being done, you should at least be observant, and then chart your observations relating to the patient’s condition at the time of the test.

Physical activity is known to affect certain tests. After 20 minutes of strenuous exercise, serum potassium is decreased by about 8 percent; while SGPT (ALT) was raised by 41 percent. Heavy exercise will also increase the presence of other enzymes that are released into the bloodstream by the muscles under stress.

Patient Posture:

There is a little known fact that the patient’s posture can affect lab values obtained from certain tests. There have been differences noted in lab values in patients who have been in a recumbent or supine position as opposed to those who have been standing or ambulatory for long periods of time. The difference in these lab values have been attributed to shifts in body fluids. Fluids tend to stay in the vascular compartment (bloodstream) when the patient is recumbent or supine. This tends to dilute the blood. There is a shift of fluids to the interstitial spaces upon standing or ambulation. The lab tests that are the most affected by this phenomenon are proteins (enzymes, albumin, globulins) and protein-bound substances such as triglycerides, cholesterol, calcium and iron.

For example, ALT (alanine aminotransferase) has been known to increase up to 14% when the patient goes from supine to the erect position. Patients who are having any of these above tests performed, should be told to avoid prolonged standing prior to the venipuncture. It takes about 20 to 30 minutes to equalize fluid shifts due to changes in position.

Food Restrictions:

There is usually no special diet requirement for most “routine” lab tests or procedures. However, each nurse should be aware of tests that do require special food restrictions. Some tests require fasting prior to the test. Be sure you inform your patient verbally and in writing. Be sure that the staff is informed of any food restrictions. It is no secret that many tests and procedures had to be canceled at the last minute because the patient ate some food. Be sure to mark the patient’s chart, diet list, and put signs in their room. Many hospitals have a specific procedure to follow for NPO. Be sure to follow this procedure and follow-up on keeping them NPO, if required for testing or for the procedure. Also remember that some tests/procedures might require that the patient consume a light meal, a liquid meal, or other special diet.

Drug Considerations:

Today, many pharmacologic agents are being used to treat disease conditions and for prophylaxis. The nurse must be aware and informed concerning interactions of these drugs and their effects on lab tests and diagnostic tests. For example, some oral contraceptives increase the values of iron, transferring, triglycerides, and ceruloplasm. Drugs toxic to the liver or kidney, could cause an increase in organ function tests (liver function tests, etc.) There are so many drugs in use today, you must have a reference available to use when your patient is going to be given a sensitive test or diagnostic procedure.

Next: Chapter III Hematology Blood Tests