Chapter I Introduction to the Course Continued
Introduction to the Course
This course presents the latest updates on select Laboratory Tests and Diagnostic tests used in most health care facilities today. Not ALL lab tests will be included in this course. Our objective with this text is to present nurses with a guide to the nursing considerations of some of the most commonly used laboratory tests and some select diagnostic tests. We will also include updates on some less frequently used tests. This course was not designed to be a lab manual that you carry in your pocket at the hospital. You should study each section of this text, in order to gain new information about lab tests. Keep in mind that lab testing procedures will vary from state to state and even fro one hospital to another hospital. Different facilities even use different standards from one another. Therefore, a “NORMAL” value at one facility may not be the same at another facility. If a particular lab test is not being used in your facility, you may still find the nursing considerations of value to you in your nursing practice.
This text is divided into large sections which present a group of similar lab tests. For example, coagulation studies represent the large group of blood tests performed on whole blood, and they are used for the detection of abnormalities in the blood’s clotting abilities. If the test results are abnormal, it could indicate one or more of many different problems. When you are studying the text, keep in mind that the tests in each group may have far-reaching implications for the nurse.
Be prepared to include lab tests in your daily care plan. Many nurses do not recognize the importance of lab tests because they feel that the doctor is responsible for interpreting the tests. This is not entirely true. The nurse must also have basic knowledge of lab tests in order to recognize trends that affect patients and in order to develop a good nursing care plan.
It is vitally important that you understand the difference between our use in this book of the terms Diagnostic Tests and Laboratory Tests. We will therefore repeat the definitions as we will use them in this text. In general, a diagnostic test is a very broad term. A Diagnostic Test is any inquiry into a pathological condition.
However, in this text, we will use diagnostic test to refer to the more sophisticated studies involving more than just examining a patient or just analyzing blood.
Yes, you could say that a blood test is a diagnostic test.
Yes, you could say that a physical examination is a diagnostic test.
Yes, you could say that taking a patient history is a diagnostic test.
However, for our text, we will say that a diagnostic test is a test that involves some type of sophisticated diagnostic equipment and/or lab tests. We will not be referring to those simple blood tests under our category of diagnostic tests. We will use simple blood tests and other simple lab tests as separate categories. We do this because in most acute hospitals today, blood tests have become very “routine” procedures. In the clinical area, they are not commonly referred to as diagnostic studies.
Introduction to Normal Values (Reference Ranges)
Your patient, Mr. Jones, a 54-year old male was admitted this morning with GI bleeding. It is 11:30 P.M. and his CBC results from earlier this evening (5:00 p.m.) have just been placed on his chart. The results reported on the lab slip are within “normal” range. However, the results are in the “low normal” range. The RBC count is 4.6, the total Hgb is 14.5, and Hct is 42.5%.
The patient (at 11:30 p.m.) has become slightly lethargic, sleepy, and slightly pale. The lab test results were not called to the doctor because they were within the normal limits. However, this was at 5:00 p.m. and it is now 11:30 p.m. What do you do? Do you call the doctor at 11:30 p.m.? Do you wait until the morning when another CBC is scheduled?
Well, in this case it is obvious that the patient is getting worse and you should take immediate action. However, the lab test results were still in the “normal range” even though the patient was getting worse. Keep in mind that you should evaluate the test results with many other factors; such as the patient’s condition, previous results, patient’s position, and many other factors.
What is a “normal” lab test results?
What factors influence the results of lab tests?
How do you interpret “normal” test results?
Do normal results HAVE TO BE interpreted?
The nurse should always keep in mind that the “normal” values given in this workbook (and in any reference book) should be considered only as “guidelines” of what is normal or abnormal. There are many variables that must be considered when interpreting the results of any laboratory or diagnostic test.
Patient Factors:
The time of day, fasting, postprandial, supine, upright, age, gender, climate, effects of drugs, and the effects of diet may all affect test results.
The characteristics of test population may also affect results. It is essential that the nurse use the reference ranges from the laboratory that is performing those particular tests, which have been determined for the laboratory’s own procedures, patient population, and so forth. Too many misunderstandings occur from attempts to apply reference ranges from one laboratory to test results from another laboratory. Misinterpretation of laboratory data due to this error, as well as from overemphasizing the significance of borderline values, has caused immeasurable emotional pain and economic waste for innumerable patients.
Also, variations of the normal range of results affect the reported test results. Based on the statistical definition of “normal” as within the 95% range of values, 5% of independent tests will be outside this normal range in the absence of disease.
If 12 tests are performed, at least one abnormal result will occur in 46% of normal persons; for 20 tests, 64% of normal persons will have at least one abnormal result. The greater the degree of abnormality of the test result, the more likely that a confirmed abnormality is significant or represents a real disorder. Most slightly abnormal results are due to pre-analytic factors.
Laboratory Factors:
Lab situations to consider are: instrumentation (lab equipment used and blood draw equipment used), child or adult, laboratory methodology for performing the tests, laboratory techniques used, the actual lab procedure may yield false-positive or false-negative results, chemicals or reagents used in the lab may be out-dated or contaminated or defective, clerical errors may occur that will give wrong test results, technical errors (problems with the machines that perform some automated tests) may occur that give false results, a variety of human errors in the la may occur (mixing the wrong chemicals, wrong proportions, etc.).
Clinical Factors:
Special notations should be made on the laboratory test request form when it is particularly germane to a test: time when the blood is drawn1, relation to meals (glucose), intravenous infusions (electrolytes), source of specimen (arterial, venous, capillary). An individual’s test values tend to remain fairly constant over a period of years. When performed in a good laboratory with comparable technology, comparison of results with previous values obtained when the patient was not ill (if available) are often a better reference value than normal ranges.
Summary:
In regards to “normal” lab values, the nurse should remember to be suspect of ALL lab results, Remember that if the results are normal, you should still assess the patient for any abnormal signs and symptoms. If the lab results are out of the normal range, be sure to again, assess for any possible adverse signs and symptoms related to the abnormal values. Each nurse still has the obligation to carefully assess the patient even if the lab results are normal and especially if they are abnormal.
Look for “trends” in lab results. A trend, for example, means that you notice the Hemoglobin is “normal”, but it is slowly going down. This could indicate that there is a slow GI bleed or similar problem. Assess for patient conditions or patient factors that may indicate a problem; even if the lab results are normal. In summary, I guess I am saying, don’t always believe the lab results. Use your assessment skills and the nursing process before you believe that the patient is “normal”.
1 Time when the blood is drawn is important when the tested component is subject to marked diurnal variation (cortisol, iron).
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