POST ANALYSIS

• Decision-Making

  Laboratory results must undergo a two step postanalytic review for analytic correctness (using delta checks, linearity ranges, etc) and for clinical significance for the patient (applying critical values, reference ranges, pretest and post-test probability, etc)
• Flags


  Can indicate a problem with the specimen (e.g the presence of an interfering substance) or an issue with the result (e.g a numeric value outside the analytic range)
• Causes of Frequent Inadequate Samples

  Presence of high concentrations of interfering substances in the specimen, most commonly: lipids (lipemia), hemoglobin (hemolysis), paraproteins (gammopathies), bilirubin (icterus)
• Flags for Specimen that Require Additional Analysis with Another Method

  Samples that could potentially contain qualitative abnormalities (e.g atypical lymphocytes, platelet clumps, red cell fragments) are flagged for a preparation of a blood smear and further evaluation
• Flags for Problematic Results

  1. If the analyte falls above the linear range many instrument can automatically dilute and reanalyze the sample

  2. If an analyte concentration falls below the linear range, the sample is usually reported as less than the limit of detection
• Delta Checks


  Comparing lab results with results from previous results with the same patient
• Reference Intervals


  The range of values into which 95% of non diseased individuals will fall
• Critical Values


  Laboratory results that may represent a life threatening situation that may not otherwise be readily detectable, must be reported immediately to a health care provider for necessary medical interventions
• Sensitivity


  The probability of a positive result in a person with the disease
• Specificity


  The probability of a negative result in a person without disease
• Screening Test


  Require high sensitivity so that no case is missed
• Confirmatory Test


  Require high specificity to be certain of the diagnosis
• Positive Predictive Value


  The probability that a positive test indicates disease, the proportion of persons with a positive test who truly have the disease
• Negative Predictive Value


  The probability that a negative test indicates absence of disease
• Likelihood Ratio


  The ratio of the probability of a given test result in the disease state over the probability of the same result in the non disease state
• 4 Types of Anemia

  • Iron deficiency
  • Anemia of chronic disease
  • Hemolytic anemia
  • Macrocytic/Nutritionally deficient anemia
• Increased Red Cell Distribution Width (RDW)


  • Cell histogram correlates a degree of anisocytosis
• Elevation of LAP Score


  • Differentiate Leukemoid reaction vs Chronic Myelogenous leukemia
• Presence of Spherocytes


  • Signify presence of hemolytic anemia
• Presence of Codocytes


  • Signify presence of thalassemia
• Prolonged PT

  • Signify presence of factor VII deficiency
• Prolonged APTT


  • Signify presence of factors XII, XI, IX, VIII deficiency
• Prolonged PT and APTT

  • Signify presence of factors I, II, V, and X deficiency or presence of lupus anticoagulant
• Urinary Sodium, Potassium, & Osmolarity


  • Can readily determine the causes of hyponatremia and hypernatremia
• Liver Function Test


  • Can distinguish different diseases of the liver: hepatitis, cirrhosis, biliary disease, space-occupying lesions of the liver, passive congestion, and fulminant hepatic failure
• Renal Failure


  • Can be readily diagnosed by observing elevated blood urea and nitrogen and creatinine
• Blood Gas Results


  • Allow determination of the causes of metabolic versus respiratory alkalosis and acidosis
• Elevation of Cardiac Troponin


  • Diagnostic of myocardial infarction
• Elevation of Serum Procalcitonin


  • Indicates sepsis or blood infection
• Elevation of Serum C-Reactive Protein (CRP)


  • Indicate inflammatory disease
• Elevation of Serum Amylase and Lipase


  • Point to acute pancreatitis
• Elevation of Serum Glucose and Absence of Insulin


  • Indicates diabetes mellitus
• T4 & TSH


  • Serum levels can be used to diagnose primary or secondary hypothyroidism or hyperthyroidism
• Cortisol and ACTH


  • Serum levels are for hypoadrenalism/ hyperadrenalism
• Elevation of Eosinophils


  • Allergy and parasitic infections
• Presence of Cysts/Eggs/Ova/Larvae


  • Diagnostic stage of parasites
• Positive Culture Along with Corresponding Biochemical Tests


  • Provide better diagnosis of bacterial, viral, fungal infections
• Presence of Dysmorphic and Blood Cell


  • In urine, it indicates glomerular hematuria/bleeding
• Presence of RTE Cell (Bubble Cell)


  • In urine, it indicates acute tubular necrosis
• Bayer's Theorem 


  Uses information about test characteristics (sensitivity and specificity) and disease prevalence (pretest probabilities) to obtain the post-test probability of disease given a positive test