Laboratory tests

Laboratory tests

1. Diagnostic Testing

   • add information to pt database
   • Screening
     • identify risk factors
     • asymptomatic patients
   • Diagnosis
     • Est. of exclude press. of disease
     • symptomatic patients
   • Patient Management
     • evaluate severity of disease
     • estimate prognosis
     • monitor course of disease
       • progression
       • stability
       • resolution
     • Detect disease recurrence
     • Select Meds and adjust therapy
   • Performance of Diagnostic Tests
     • Preparation
       • Test
         • specimen
           • most crucial element for properly conducted test
       • Patient
         • Fasting
           • glucose
           • triglyceride
         • posture
           • renin
         • Na intake
           • aldosterone
         • Strenuous Exercise
           • creatine kinase level may be abnormal
     • Specimen Collection
       • patient ID
         • 2 identifiers
       • labeling
         • collection time
       • Avoid
         • drawing around IV line
           • fluid/drugs
         • Excessive tourniquet time
           • Hemoconcentration
           • increased Ca
         • Delay in delivery to lab
       • cell lysis
         • increased K and Lactate dehydrogenase
       • Special Handling and Storage
         • ABG

2. Diagnostic Test Characterisitcs

   • Reference Interval
     • REPORT QUANTITATIVE RESULTS
     • Method and laboratory specific
     • rep results of 95% of pop presumed to be healthy
     • consider in light of patient parameters
   • Accuracy
     • correspond to true value
     • maximize
       • calibrate equipment
       • external proficiency testing
   • Precision
     • measure of reproducibility when repeated on same sample
     • IDEAL TEST IS BOTH ACCURATE AND PRECISE
   • Interfering factors
     • considered in interpretation of results
       • external
         • medications
       • Internal
         • abnormal physiologic states
   • Sensitivity
     • ability to detect disease
       • 90% sensitive test gives positive results in 90% of diseased patients
         • 10% of diseased patients will get negative results, aka false negative
         • high sensitivity
           • useful to exclude diagnosis
     • % of patients w/ + test for disease
   • specificity
     • ability to detect absence of a disease