Clinical Chemistry - Blood Samples Collection - Chapter 1 Introduction PDF

Clinical chemistry Objectives List List the units used in clinical chemistry laboratory. Mention Mention basic needs of electronic reporting of results. List List types of reagent that used in clinical laboratories. List List supplies used in clinical laboratories. Line O...

Clinical chemistry Objectives List List the units used in clinical chemistry laboratory. Mention Mention basic needs of electronic reporting of results. List List types of reagent that used in clinical laboratories. List List supplies used in clinical laboratories. Line Out line laboratory mathematics and calculations Mention Mention specimens received in clinical chemistry laboratory  Clinical chemistry: The primary purpose of a clinical chemistry laboratory is to facilitate the correct performance of analytic procedures that yield accurate and precise information, aiding patient diagnosis and treatment. The achievement of reliable results requires that the clinical laboratory scientist be able to correctly use basic supplies and equipment and possess an understanding of fundamental concepts critical to any analytic procedure.  Units Any meaningful quantitative laboratory result consists of two components. First component represents the actual value, and the second is a label identifying the units of the expression. The number describes the numeric value, whereas the unit defines the physical quantity or dimension, such as mass, length, time, or volume. Blood glucose = 100mg/dl Results may be expressed in mg/dl g/l mmol/L mEq/L Although several systems of units have traditionally been used by various scientific divisions, the Système International (SI), is preferred in scientific literature and clinical laboratories and is the only system used in many countries. This system was devised to provide the global scientific community a uniform method of describing physical quantities System International (SI) Adopted internationally in 1960 Preferred in scientific literature and clinical labs Based on metric system Includes basic (m, kg, s) and derived (Hz, C) units Uses standard prefixes: nano, micro, milli, kilo, mega, giga, tera Electronic Reporting of Results No uniform standard exists, but there are many different data management systems in use by health care agencies that all use laboratory information such as , American Society for Testing and Materials (ASTM) and there is there an agreement in most systems that each test: Name should be clearly identified and should have its unique code and should include the value and the unit or the appropriate abbreviation. Reference ranges, for most clinical chemistry tests, are not universal and in those instances need to be included for proper interpretation  Solution Properties Terms and definitions related to the solution: Solute: a substance dissolved in a liquid Analytes: biologic solutes Solvent: liquid in which solute is dissolved Solution: solute plus solvent Concentration: Analyte concentration in solution can be expressed in many ways. Routinely, concentration is expressed as percent solution, molarity, molality, or normality Laboratory Mathematics and Calculations 1-Concentration Calculations: include Percent solution, Molarity, Normality, Specific gravity, Conversions 2-Dilutions Calculations: Two types Simple dilutions and Serial dilutions 3-Graphing and Beer’s Law: Beer-Lambert Law (Beer’s law) establishes relationship between concentration and absorbance in many photometric determinations. 4-Enzyme calculations  Specimen Considerations The process of specimen collection, handling, and processing remains one of the primary areas of preanalytic error. Careful attention is necessary to ensure proper subsequent testing and reporting of meaningful results. All accreditation agencies require laboratories to clearly define the procedures used for proper collection, transport, and processing of patient samples and the steps used to minimize and detect any errors.  Types of Samples Whole blood: both liquid portion (plasma) and cellular components (red and white blood cells, platelets) Plasma: clear yellow supernate Serum: remaining liquid after clotting Arterial blood: to measure blood gases and pH Urine Cerebrospinal fluid Paracentesis fluids: pleural, pericardial, peritoneal Amniotic fluids Blood sample specimen collection and processing Phases of the testing process Reception, preparation of Patient, collection of specimen, separation, transportation (if Preanalytic phase: present), storage and dispatch of sample for processing. Achievement of QC program take place mainly in Analytic phase: this phase mainly (processing of sample) Postanalytical Beginning from calculation, writing results, phase: recording results and dispatch of result. The pre-analytical stage is the most important and can be critical to patient wellbeing The analytical stage and post analytical stages depend primarily on the Quality and Integrity of the specimen submitted to the laboratory (Pre-Analytical) Laboratory staff involved in specimen collection have a direct impact on the outcome of patients lab results Remember Since preanalytical errors have been reported to account for more than two thirds of all laboratory errors. It is clear that regardless of the advances of laboratory technology at the analytical stage, improvements in preanalytical areas will remain to be a challenge.  Many things can go wrong in the preanalytical area These often result in sub-optimal specimen quality, the implications of which will be “Errors in patient test result” What are preanalytical variables ? These are variables that can occur from the time when the test is ordered by the physician until the sample is ready for analysis Preanalytical variables can account for up to 75% of laboratory errors Examples of possible preanalytical variables 1. Patient preparation. 2. Proper sample selection. 3. Proper collection and transportation. 4. Details of the patient and specimen identification. 5. Selection of appropriate samples. 6. Selection of right test method. 7. Right quality & Right labeling. Patient Identification: It is important to identify a patient accurately so that blood is collected from the correct person. Drawing blood from the wrong person, or labeling the correct patient’s sample with a different patient’s label can certainly contribute to laboratory error. (Mislabeling ???) Patient Preparation: Prior to collecting specimens for chemistry, certain patient variables need to be considered. For certain chemistry analytes, such as glucose and cholesterol, patients need to be fasting for at least 12 hours prior to venipuncture. Other analytes, such as cortisol and adrenocorticotropin, have diurnal variations, where the analyte is at its highest level in the morning, and the levels gradually decrease during the course of the day. Site Preparation Prior to venipuncture, site should be cleansed with alcohol. Cleansing starts at the center of the vein, and should continue outward in concentric circles. Alcohol should be allowed to air dry to ensure that the specimen is not contaminated with alcohol, as this can lead to hemolysis. Hemolysis can result in elevation of such analytes as potassium, lactate dehydrogenase (LD), iron and magnesium. Tourniquet Application and Time: Tourniquet should be applied approximately three to four inches above the venipuncture site, should be on the arm no longer than one minute. A good rule of thumb to determine the one-minute tourniquet time is to remove the tourniquet when blood starts to flow into the first tube of blood being drawn. Prolonged tourniquet time can lead to an increase in various chemistry analytes, including serum protein, potassium and lactic acid due to hemoconcentration of blood at the puncture site. The Pre-Analytical process for sample Order Test Collect Sample Transport to Lab Receive in Lab Prepare for Testing Transport to Sections Affect of diet The nutrient of the patient may sometimes strongly affect the concentration of a number of analytes in blood. It may even be important to keep person on special diet prior to investigation of the blood, so as to obtain more accurate information about metabolic status. Analytes which particularly affected by nutritional state include Calcium and phosphate increase after large quantity of milk. Glucose increase after ingestion of large quantity of carbohydrate. Triglycerides increase after ingestion of fat-rich meal and urea elevated after meat ingestion. Ingestion large volume of water may result in false normal urine glucose concentration (diabetic patient) and dehydration may cause apparently elevated urine glucose concentration. Ethanol ingestion acutely change activities of Alanine Amino Transferase (ALT) and Aspartate Amino Transferase (AST) Exercise and stress Physical exercise may cause pronounce change in enzymes activity occurring in muscle, creatine kinase (CK) as well as AST increase markedly after physical exercise. Hematuria may develop after heavy exercise in long distance runner. Prolonged physical exercise has been found to considerably decrease the level of various hormones like epinephrine and sexual hormones. Stress increase ACTH causing cortisol levels to rise, catecholamines Medullary catecholamine products serve as first responders to stress by acting within seconds Posture of the patient during blood sampling Other source of change in concentrations of analytes in blood is the position of the patient during blood sampling. Change in concentration or activity are more pronounced when blood is taken from healthy person changing position from horizontal to upright, than changing resulting from technical factor during investigation in laboratory with good practice, this change may reach in certain analytes up to 15% like seen in ALT, AST, ALP, protein and albumin Circadian variation Physiologic variation refers to changes that occur within the body, such as cyclic changes (diurnal or circadian variation) Even in an individual the concentration of certain analytes may change following a biorhythm. Typical examples following a circadian (day) rhythm are hormones like corticosteroid hormones and thyroid hormones. Evidence of biorhythmic changes with longer periodicity is demonstrable in females, as during the menstrual cycle serum cholesterol concentration is lowest at the time of ovulation and plasma urea and creatinine concentration increase during the phase of menstruation, while the concentration of serum iron, phosphate and protein is lower, these changes are known as lunar-monthly rhythm. Non periodic changes Non periodic changes: the occurrence of non-periodic changes as pregnancy may alter reference value of number of common analytes such as transaminases activities, lipids and hormones.