Selecting and Interpreting Lab Results -

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1 Selecting and Interpreting Lab Results -

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9 e.g chest pain

10 e.g PT PTT in bleeding disorders; blood glucose in diabetes etc

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16 Test ordering- direct order entry by person requesting the test is best. If transcribed by ward/office staff, transcription errors can occur.

17 Specimen collection and transport Patient identification and specimen labeling accuracy are vital. Consider: Patient A is blood type A and patient B is blood type B. Both patients have blood drawn for type and screen at the same time. The tubes are mislabeled. If patient A needs blood, (s)he would be given type B blood (due to the incorrectly labeled tube), leading to an acute hemolytic transfusion reaction and possible death. Ensure that adequate volumes are collected and that specimen are put in the correct containers.

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20 When a medical practitioner orders pathology tests, it is to assist in making a diagnosis. Most modern pathology laboratories offer a comprehensive range of pathology services with many specialised departments encompassing all the major disciplines. The laboratory is supervised by a team of dedicated pathologists and within each department there are a group of professional laboratory scientists and technicians. Before we delve into the tests we order, let us say some important words about their interpretation.

21 Normal Reference Ranges A. Essentially all lab tests have normal reference ranges. B. Each lab must determine its own reference ranges. C. These reference ranges are obtained by running the test on specimens from healthy persons of various ages and ethnic backgrounds that reflect the patient population of the lab. D. The normal reference range includes 95% of the normal population. E. 2.5% of normals will be above and 2.5% will be below the reference range.

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25 Interpretation of Lab Test Profiles The various multiparameter blood chemistry and hematology profiles offered by most labs represent an economical way by which a large amount of information concerning a patient's physiologic status can be made available to the physician. However, one must be careful in the interpretation of abnormalities of each of the parameters.

26 Reference ranges ("normal ranges") Because reference ranges (except for some lipid studies) are typically defined as the range of values of the median 95% of the healthy population, it is unlikely that a given specimen, even from a healthy patient, will show "normal" values for all the tests in a lengthy profile. Therefore, caution should be exercised to prevent overreaction to miscellaneous, mild abnormalities without clinical correlate.

27 Caveats in interpreting Lab Values A. Never use a single out-of-reference range value to make a diagnosis. A single abnormal value may be spurious and can be due to many reasons, such as lab variability, poor phlebotomy technique, delayed specimen processing, etc. Always look for a trend abnormal results within two or more successive samples. B. If the patient is under 60, look to attribute all abnormal lab findings to a single cause. Only if there is no way to fit all the abnormal findings to one diagnosis should multiple diagnoses be considered.

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47 Abnormal Lab Results Don t Always Indicate Problems Interpreting lab results can be one of the more complex tasks facing physicians. Even more challenging is explaining these results to patients in a way that is respectful, accurate, and does not provoke unnecessary anxiety or confusion. All lab results are published and reported within a range defined as "normal". Normal values are derived from measuring those values in large numbers of healthy people and then selecting a range that includes the most frequently recorded results. The most common values are then selected as normal that means values that are normal for some people, but less common, technically become "abnormal".

48 To underscore the situation, when lab results are reported, the report lists the normal range first followed by the patient s actual value. Any number below or above the normal range is indicated on the lab report and may loosely be interpreted as abnormal.

49 This is where the challenge arises, and one of the main reasons why physicians are encouraged to only order tests that are based on the clinical condition of the patient at the time of evaluation, as opposed to ordering a battery of tests. Several problems can result, as shown in the following examples. Let's say a specific test is ordered for a person who is generally in good health. The test results fall just outside the "normal" range. Often, a physician will determine that this is of no clinical significance and choose not to pursue it further yet to be truthful, a phone call is made to the patient stating that their test was abnormal, but not to worry about it. For the patient, of course, this is easier said than done.

50 Another scenario occurs when several tests are ordered to establish information on a specific condition and a test expected to be normal is not. When considered in the context of the patient s health, the challenge often faced is whether to go on a "hunting expedition" of sorts that can lead to more intense and invasive forms of testing. This type of investigation may put the patient at risk for complications and cost large sums of money, often to no purpose, while generating high levels of anxiety. Sometimes test results are just plain wrong maybe due to an error in the laboratory or a malfunction of the testing equipment. Under these as well as other circumstances, and so long as the patient is well, the next best step is to repeat the test.

51 The physician must be completely honest and give clear, accurate explanation of an unusual result. The doctor must not be dismissive, and try to ensure that patients are comfortable with the explanation.. Do not just tell them that all is really fine and that there is nothing to worry about.