ICM Day 9: Intro to Laboratory Medicine PDF

ICM Day 9: Intro to Laboratory Medicine Topic: Introduction to Laboratory Medicine Learning Objectives 1. List & justify appropriate reasons for ordering diagnostic tests & identify inappropriate utilization of diagnostic testing services....

ICM Day 9: Intro to Laboratory Medicine Topic: Introduction to Laboratory Medicine Learning Objectives 1. List & justify appropriate reasons for ordering diagnostic tests & identify inappropriate utilization of diagnostic testing services. a. Don’t order a test unless it will change or help your management b. Need to have a diagnosis code for every lab order i. Lab won’t process it without it!! c. If a test is ordered an it is determined to not be medically necessary (by Medicare or the insurance company) for the diagnosis you assigned, the insurance company will not pay for the test d. Screening tests: to identify risk factors for disease and to detect occult disease in ASYMPTOMATIC persons → early interventions to reduce disease morbidity and mortality e. Criteria for optimal screening tests: i. Characteristics of population/patient 1. Sufficiently high prevalence of disease 2. Likely to be compliant with subsequent tests and treatments a. Example: A homeless person is less likely to be able to attend follow up tests/treatments ii. Characteristics of Disease 1. Significant morbidity and mortality 2. Effective and acceptable treatment available 3. Presymptomatic period detectable 4. Improved outcome from early treatment iii. Characteristics of Test: 1. Good sensitivity and specificity 2. Low cost and risk 3. Confirmatory test available f. Diagnostic tests: Help establish or exclude the presence of disease in SYMPTOMATIC persons i. Assist in early diagnosis after onset of signs and symptoms ii. Assist in developing a differential diagnosis iii. Help determine the stage or activity of disease g. Pain Management: i. Evaluate the severity of disease and estimate prognosis ii. Monitor the course of disease (progression, stability, or resolution) iii. Detect disease recurrence iv. Select drugs and adjust therapy 2. Discuss the concepts of risk/benefit & cost-effectiveness in choosing diagnostic procedures. a. The cost of the test itself must always be considered → panel vs one test or frequency of testing b. Associated risks c. Potential for additional testing d. ALWAYS need to ask yourself → will the results of testing change the treatment plan? 3. Explain & appropriately use the following terms in the context of medical tests: normal, abnormal, average, specificity, precision, & sensitivity. a. Qualitative: either positive or negative → pregnancy, drug screens, etc b. Quantitative: measured amount reported in mass or volume c. Reference intervals (range): establishes a normal range → lab & population dependent… determined by sampling a “healthy” population i. Can be different depending on the region the sample was taken from 1. Example: Reference ranges for hemoglobin and hematocrit are different depending on the region due to altitude!! ii. 95% of the result determine the normal range iii. The top and bottom 2.5% fall outside of the reference range d. Accuracy: determined by its correspondence with the true value (center of the bullseye) i. Quality control measures e. Precision: a measure of the tests reproducibility i. A test is imprecise if results vary significantly on repeat measurements ii. Even precise tests will vary slightly upon repeating and this is referred to as the coefficient of variation f. Sensitivity: the ability of a test to detect the PRESENCE of disease (RULING OUT DISEASE) i. Percentage of patients WITH disease in whom the test is positive ii. Example: a test with a sensitivity of 90% gives positive results in 90% of diseased patients and negative results in 10% of diseased patients 1. Aka 90% true positives and 10% false negative iii. True positive (TP): abnormal test results occurring in individuals who have the disease iv. False negative (FN): Normal test results occurring in individuals who have the disease v. Sensitivity = TP/ (TP+FN) vi. Example: Need a highly sensitive test to determine the presence of HIV vii. SNOut: a highly Sensitive test with a Negative result is helpful for ruling Out the disease g. Specificity: the ability to detect ABSENCE of disease and is expressed as the percentage of patients WITHOUT disease in whom the test is negative (RULING IN DISEASE) i. Example: A test with a 90% specificity gives negative results (true negatives) in 90% of patients without disease and positive results (false positives) in 10% of patients without disease 1. Aka 90% are true negative and 10% are false positives ii. Ability to detect true negatives → the higher the specificity the fewer the false positives 1. True negative (TN): normal test results in a disease-free healthy individual 2. False positive (FP): abnormal test results in a disease free healthy individual 3. Specificity: TN/ (TN+FP) 4. Example: a highly specific test to check for gout would be an evaluation of the joint fluid for the presence of urate crystals 5. SPIn: a highly Specific test with a Positive results is helpful for ruling In the disease 4. Discuss the population variables affecting test reference values and the appropriate use of these values to interpret patient test results. a. Physiological factors: medications, altitude, occupational/environmental exposures, age, gender, exercise, diet, tobacco use b. Pretest Probability: the likelihood the patient has the abnormality that you are testing for based on risk factors, symptoms, history, and physical exam i. The higher the pretest probability, the more likely you will get a true test result ii. To help clinicians determine pretest probabilities, clinical guidelines have been developed based on scientific studies iii. Example: a patient seen in a medical clinic in Cheyenne, WY for fever and chills is more likely to have a UTI than malaria, which would be much more probable diagnosis in central Africa iv. A physician with more experience have a better pretest probability 1. Can better predict if a test will be positive or negative based on patient hx, symptoms, and physical exam 5. Discuss the advantages/disadvantages & appropriate applications for single test ordering versus using chemistry profiles (panels). a. Single tests are less expensive than the whole panel but it depends on what you are looking for and the patient population  i. Example: many health fairs check just total cholesterol to screen for lipid disorders. If the total cholesterol is abnormal then you would need a lipid panel prior to treating the patient b. Need to approach every patient in a cost-saving manner, don’t spend more health care dollars than necessary 6. Identify the commonly included chemistry analyses for each of the following profiles a. Basic metabolic profile: Na, K, Cl, CO2, GLU, BUN, Creatinine, Ca b. Comprehensive metabolic profile: Na, K, Cl, CO2, GLU, BUN, Creatinine, Ca, TP, ALB, AST, ALT, ALP, T. BILI c. Liver function profile: ALB, AST, ALT, ALP, T. BILI, D. BILI d. Renal function profile: Na, K, Cl, CO2, GLU, BUN, Creatinine, Ca, ALB, InorP e. Electrolytes: Na, K, Cl, CO2 f. Thyroid function profile: TSH, Free T4, Free T3, Total T4, Total T3, Thyroid antibodies g. Lipid profile: total cholesterol, LDL, HDL, VLDL, triglycerides 7. Identify the various units of measurement utilized in analyzing chemical constituents a. Units of measurement are important when comparing results from different labs as they may report them differently i. Example: Vitamin D is reported as either ng/mL or nmoles/L, normal is more than 20 ng/ml (aka 50 nmol/L) 8. Describe & compare the sensitivity of the various analytic techniques used in the clinical laboratory a. Analytic techniques in clinical laboratories vary widely in their sensitivity, depending on the technology, methodology, and the specific analytes being measured. b. Example: Mass spectrometry is highly sensitive compared to Spectromatography  i. Mass Spectrometry > PCR > ELISA ≈ Fluorescence Spectroscopy > Flow Cytometry > HPLC ≈ Electrochemistry > Spectrophotometry 9. Discuss and interpret the Complete Blood Count (CBC) components. a. Complete Blood Count: WBCs, RBCs, Platelets b. WBC count: total number of all WBCS in the sample i. WBC differential: percentage of different types of WBCs 1. Neutrophils 2. Lymphocytes 3. Monocytes 4. Eosinophils 5. Basophils c. RBC count: actual number of RBCs i. Hemoglobin: the amount of oxygen carrying protein in the blood ii. Hematocrit: the percentage of a person's blood that consists of RBCs iii. Reticulocytes: new baby RBCs iv. RBC indices: IMPORTANT FOR EVALUATION OF ANEMIA!!! 1. Mean Corpuscular Hemoglobin (MCH): average amount of oxygen carrying hemoglobin 2. Mean Corpuscular Volume (MCV): average RBC size 3. Mean Corpuscular Hemoglobin Concentration (MCHC): average percentage of hemoglobin inside the RBCs 4. Red Cell Distribution Width (RDW): variation in the size of the RBCs 10. Discuss and interpret the urinalysis and urine culture and sensitivity results. a. Macroscopic evaluation → color, clarity, and odor or urine b. Urine dipstick chemical analysis → pH, specific gravity, protein, glucose, ketones, blood, leukocytes, nitrates, bilirubin/urobilinogen c. Microscopic urinalysis → RBCs, WBCs, epithelial cells, casts, crystals, bacteria d. Urine culture → colony count and identification of organisms e. Sensitivity testing → antibiotic sensitivity and minimum inhibitory concentration (MIC) 11. Explain the basis for diagnosis-related groups (DRG) assignment of appropriate laboratory testing. a. Medicare has established extensive guidelines for ordering laboratory tests on outpatients b. Every diagnostic PROCEDURE has a Current Procedural Terminology (CPT) code c. Every DIAGNOSIS has an ICD-11 code (International Classification of Diseases) i. More important for how PAs practice d. The ICD-11 code is assigned to a Diagnosis Related Group (DRG) for HOSPITALIZED patients e. Approved CPT codes are linked to ICD codes and DRGs 12. Discuss the reasoning process & apply diagnostic test results in the clinical decision-making process. a. Clinical Assessment: collect comprehensive information about the patient's symptoms, medical history, lifestyle, and any relevant factors and do a physical exam to identify signs that support/refute a potential diagnosis b. Differential diagnosis: potential diagnoses ranked based on the likelihood of each condition c. Selection of Diagnostic Tests: ordering tests to confirm or exclude conditions on the differential diagnoses → should be chosen based on sensitivity, specificity, cost-effectiveness, and relevance to the patient’s clinical presentation i. Before ordering a test, the clinician assesses the pre-test probability (the likelihood that a patient has a disease before the test result is known) to determine the value of the test d. Interpretation of Test Results: i. Confirm a Diagnosis: A positive result on a specific test (e.g., a positive culture for a particular bacterium) can confirm the presence of a disease ii. Exclude a Diagnosis: A negative result on a highly sensitive test (e.g., a normal D-dimer in a low-risk patient) can help exclude a condition like pulmonary embolism. iii. Refine Differential Diagnosis: Some results may not definitively confirm or exclude a condition but may adjust the probability of certain diagnoses, leading to further testing or re-evaluation. iv. False Positives/Negatives: Clinicians must be aware of the possibility of false-positive or false-negative results and interpret tests within the context of the entire clinical scenario e. Integration with Clinical Information: The test results are integrated with the patient’s history, symptoms, and physical findings. i. The clinician uses a combination of deductive reasoning (based on specific tests) and inductive reasoning (based on patterns and trends) to arrive at a diagnosis. ii. If test results are inconclusive or unexpected, the clinician may revisit the differential diagnosis, order additional tests, or modify the treatment plan. f. Clinical Decision-Making: making a final diagnosis, selecting appropriate treatment, and monitoring patient’s response g. Communication & Documentation: explaining the test results, diagnosis, and treatment to the patient and documenting it in the medical record