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Clinical Enzymology

Key Points Enzymes are protein catalysts utilized by essentially all mammalian cells in specific biochemical reactions in different organs of the body, which may also be physically located in different organelles and structures within a cell. Enzymes lower the activation energies of the chemical reactions that they catalyze so as to cause greatly enhanced rates of reaction. They do not become modified in these reactions and…

Specific Proteins

Key Points The primary structure of a protein is its linear sequence of amino acids with different side groups, which determine how the protein folds on itself (secondary and tertiary structures) and how it reacts with other molecules and cells (i.e., its molecular identity). Methods to quantitate and fractionate proteins are based on turbidimetry, colorimetry, absorption spectrophotometry, dye binding, column chromatography, electrophoresis, and immunoassays. Protein electrophoresis…

Cardiac Injury, Atherosclerosis, And Thrombotic Disease

Key Points The most important disease affecting the heart is atherosclerotic cardiovascular disease (ASCVD), caused by plaque in the coronary arteries. ASCVD can lead to thrombotic occlusion of coronary blood flow, causing an acute coronary syndrome (ACS). ACS with frank necrosis of any amount of myocardium is known as myocardial infarction ( MI ). The primary tests for diagnosing and evaluating ACS are electrocardiography (ECG) and…

Lipids And Dyslipoproteinemia

KEY POINTS Although ultracentrifugation and electrophoretic techniques are of historical significance, most useful lipid and lipoprotein testing methods are now enzymatic. Low-density lipoprotein (LDL) cholesterol is considered the primary target in assessing cardiac risk and directing therapy. LDL cholesterol can be measured directly but is usually calculated using the Friedewald equation and more recently using the Martin-Hopkins formula. The Martin-Hopkins formula has demonstrated improved accuracy at…

Carbohydrates

Key Points Normal fasting plasma glucose is less than 100 mg/dL (5.6 mmol/L), and normal glucose levels 2 hours after a 75-g glucose load are less than 140 mg/dL (7.8 mmol/L). Impaired fasting glucose (100–125 mg/dL; 5.6–6.9 mmol/L), impaired glucose tolerance (a 2-hour plasma glucose value of 140–199 mg/dL [7.8–11.0 mmol/L] after a 75-g glucose load), or “prediabetes” (a glycated hemoglobin (HbA 1c ) of 5.7%–6.4%)…

Biochemical Markers Of Bone Metabolism

Key Points The plasma concentration of calcium, phosphate, and magnesium is dependent on the net balance of bone mineral deposition and resorption, intestinal absorption, and renal excretion. The principal hormones regulating these processes are parathyroid hormone (PTH), calcitonin, 1,25-dihydroxyvitamin D, and fibroblast growth factor-23 (FGF-23). The most common causes of hypercalcemia are primary hyperparathyroidism (elevated PTH) and malignant neoplasms (decreased PTH and usually elevated PTH-related peptide).…

Evaluation Of Renal Function, Water, Electrolytes, And Acid-Base Balance

Introduction Laboratory tests for evaluation of disorders of renal, water, electrolyte, and acid-base status are the most common procedures performed in clinical chemistry laboratories. Screening tests in most laboratories are often grouped together in a basic metabolic panel because acid-base and electrolyte disorders are seen in a high percentage of hospitalized individuals, and electrolyte disorders are frequent complications of treatment for a variety of common conditions.…

Ethics In Laboratory Medicine

Key Points Ethical behavior in professional affairs is essential to maintain trust of patients and physicians. Conflicts of interest can arise when transparency of motives and rewards is not practiced. Privacy of protected health information is mandated by the U.S. federal government under the Health Insurance Portability and Accountability Act. Following atrocities and war crimes of unethical research on human subjects during World War II, the…

Financial Management

Key Points Costs can be described in different ways depending on how they relate to laboratory operations (direct/indirect), change with test volume (variable/fixed), pertain to staffing (salary/nonsalary), or are associated with the useful life of supplies or equipment (operating/capital). Cost per reportable result is a key indicator. Reimbursement for laboratory services comes mostly from third-party payers, such as Medicare (government) and insurance companies (nongovernment/private insurance), and…

Clinical Laboratory Informatics

Key Points The practice of Pathology Informatics/Clinical Laboratory Informatics is central to all aspects of data stewardship in the clinical laboratory. Fundamental knowledge of database technology and database principles is critical to understanding key aspects of laboratory information system (LIS) operation. The LIS is an integral element of the larger enterprise-wide portfolio of information technology solutions that may be rendered as either a stand-alone vendor solution…

Quality Control

Key Points Quality control samples are assayed on a schedule to verify that a laboratory procedure is performing correctly. Interpretation of quality control results is based on acceptance criteria that will identify bias, trend in bias, or imprecision that exceeds expected method performance characteristics. In the event of an unacceptable quality control result, corrective action is taken to fix the method problem, and all patient results…

Laboratory Statistics

Key Points For statistical analyses, nominal variables can take on only a limited number of values (or categories), whereas continuous variables are used to report quantitative data. Independent variables are considered input (cause), and dependent variables are considered output (effect). Distributions of continuous data are described by a measure of central tendency (e.g., mean or median) and dispersion (standard deviation). Gaussian distributions derive from a mathematical…

Interpreting Laboratory Results

Key Points Accurate differential diagnoses can be made from a systematic study of the laboratory profiles of patients in a large majority of cases. There are basically four types of anemia: iron deficiency, anemia of chronic disease, hemolytic anemia, and macrocytic/nutritionally deficient anemia. These can be readily distinguished from one another both by the hematologic profile and simple laboratory testing. By examining the urinary sodium, potassium,…

Postanalysis: Medical Decision Making

Key Points 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 posttest probability, etc.). Reference intervals are most commonly defined as the range of values into which 95% of nondiseased individuals will fall. This definition implies that 5% of nondiseased individuals can have laboratory…

Point-Of-Care Testing And Physician Office Laboratories

Key Points Point-of-care testing refers to the scope of laboratory tests that are performed where patient care is delivered. This includes physician office testing as well as various hospital locations outside the laboratory, such as the emergency department, operating room, and intensive care unit. When performed in a physician office, simple tests (such as urine dipstick and whole blood glucose meters) are exempt from most regulations…

Analysis: Clinical Laboratory Automation

Key Points Laboratory testing has undergone revolutionary changes over the past decade. Typically, all routine chemistry and hematology testing is completely automated. Automated solutions are available for preanalytic, analytic, and postanalytic stages of laboratory testing. The degree of automation implemented in a laboratory should match its needs and can vary from a freestanding analyzer to a workcell or totally automated solution. Preanalytic automation is heavily dependent…

Mass Spectrometry and Applications

Key Points Mass spectrometry can identify and quantify analytes in human fluids and tissues. Mass spectrometry is based on volatilizing samples and ionizing the analytes of interest, which can then be identified from their times of flight (TOF) or in electric fields based on their molecular masses and the relative masses of their molecular ion fragments. New special techniques are now able to analyze patient samples…

Analysis: Principles Of Instrumentation

Key Points Many analytic determinations made in clinical laboratories are based on measurements of radiant energy that is absorbed or transmitted. The devices used to measure absorbed or transmitted light energy are photometers and spectrophotometers. The basic components of spectrophotometers include a radiant energy source, wavelength selector, cuvette holder, photodetector, signal processors, and readout devices. A reflectometer is used to measure analytes by measuring the quantity…

Preanalysis

Key Points Errors and variables in the preanalysis stage can affect test results. Patient variables include physical activity, diet, age, sex, circadian variations, posture, stress, obesity, smoking, and medication. Strict adherence to proper technique and site selection can minimize collection variables such as hemolysis, hemoconcentration, clots, and other causes for sample rejection or erroneous results. Blood collection containers are color coded based on additive or preservative,…

Optimizing Laboratory Workflow and Performance

Key Points An effective testing process requires integration of preanalytic, analytic, and postanalytic steps. An understanding of workflow is a fundamental prerequisite to any performance optimization strategy. A variety of techniques should be used to collect workflow data. These include sample and test mapping, tube analysis, workstation analysis, staff interviews, and task (process) mapping. Though technology is a critical component of every laboratory, it is only…