Clinical Pathology PDF

CLINICAL PATHOLOGY Sampling What is clinical pathology? It is is concerned with the diagnosis, screening, prognosis, follow up of treatment of disease based on the laboratory analysis of bodily fluids, blood, urine,stool and tissue. Clinical – clinical samples (blood , urine,...

CLINICAL PATHOLOGY Sampling What is clinical pathology? It is is concerned with the diagnosis, screening, prognosis, follow up of treatment of disease based on the laboratory analysis of bodily fluids, blood, urine,stool and tissue. Clinical – clinical samples (blood , urine, stool, body fluids, etc….) Pathology – study about disease. The science and practice of medical diagnosis by laboratory examination and analysis of tissue specimens (Biopsies), body fluids and other samples. Clinical pathology is subdivided into: ▪ Virology ▪ Bacteriology ▪ Clinical chemistry ▪ Serology ▪ HistoPathology Sensitive Test – Ability of test to give positive result if patient has the disease (only positive) Specificity – ability of test to give negative result if patient does not have disease (only Negative)  ◾ Based on specificity/sensitivity: Screening Tests Diagnostic Tests An ideal screening test is 100% An ideal diagnostic test is 100% specific sensitive Useful in a large sample size at risk; Useful in symptomatic individuals to establish typically cheaper diagnosis or asymptomatic individuals with +ve screening test; expensive eg : blood glucose estimation for egs: Glycated Haemoglobin estimation, screening diabetes, 7 ◾ Based on where investigation is done: Point-of-care Laboratory Investigations testing (POCT or bedside testing Acts as a precursor to laboratory Significantly higher sensitivity investigations and specificity egs: Glycated Haemoglobin estimation, Peripheral smear histpathology 8 Different types of Tests BLOOD SAMPLE COLLECTION SAMPLE COLLECTION Blood collection, or blood sampling for laboratory analysis. Three popular methods of blood collection are: 1. Arterial Sampling 2. Venous Sampling 3. Fingerstick Sampling 1. ARTERIAL SAMPLING Most commonly takes place within a hospital environment (mainly in the ICU). It is used in the identification of metabolic, respiratory, and mixed acid-base disorders, where CO2 levels require understanding or monitoring. While generally safe, the procedure can be upsetting and painful for the patient.  There are also several potential contradictions that can affect the site of the collection, such as local infection. There is also an increased risk of bleeding complications in patients with coagulopathy.  Blood gas Test: A blood gas test measures the amount of oxygen and carbon dioxide in the blood. It may also be used to determine the pH of the blood, or how acidic it is. The test is commonly known as a blood gas analysis or Arterial Blood gas (ABG) test. In general, normal values include: arterial blood pH: 7.38 to 7.42 partial pressure of oxygen: 75 to 100 mm Hg partial pressure of carbon dioxide: 38 to 42 mm Hg ABG 2. Venous Sampling Venipuncture is the most common way to collect blood from adult patients. Collection takes place from a superficial vein in the upper limb, generally the median cubital vein; this vein is close to the skin and doesn’t have many large nerves positioned close by. This reduces pain for the patient. Clean the sight with spirit allow to dry. Readily attached needle is introduced to the vein with the level facing upward at an angle of 30 – 40  Entrance into the vein is denoted by appearance of blood into the hub of the needle. Release the tourniquet an withdrawn the needle. The blood is transfer into the appropriate containers 3. FINGERSTICK SAMPLING Fingerstick or finger prick sampling involves taking a very small amount of blood from the patient, usually from the end of a finger. It is also known as Capilary blood collection. It is over quickly and requires very little in the way of preparation; therefore, reducing concern and anxiety in patients, particularly in children and nervous adults.  Clean the finger with alcohol swab and allow to dry. Hold the ball finger and make a quick puncture about ½ cm from the end using a sterile lancet, wipe the first drop as it may contains tissue fluids. The blood should floe freely, without applying pressure collect the succeeding drop for investigation. It is mainly used for : -blood sugar test -Hb estimation -Blood group -Bleeding and clotting time  COLLECTION OF BLOOD SAMPLE CAPILLARY BLOOD SPECIMENS: The specimen is obtained by pricking the patient`s finger. VENOUS BLOOD SPECIMEN: Most Commonly used method. Venipuncture is usually performed in ANTECUBITAL vein.  LABELLING Before the sample collection the tube should be labelled immediately. Requiring patients to state their full name ,and to spell their first name and last name Requiring outpatients to show a form of identification when an ID band is not in use Labeling specimen tubes in the presence of the patient. It should be help avoid errors.  TYPES OF BLOOD COLLECTION TUBES Serum : No anticoagulant or additives. Collection of serum for chemical or serological and bacteriologic studies. May be used for any procedure requiring serum. CBC or Haemoglobin: Contains EDTA (Ethylene Diamine Tetra Acetate) as the anticoagulant. Mix well Primarily for collection of hematology studies, blood bank procedures and certain chemistries. Blue : Contains sodium citrate solution as the anticoagulant. Primarily for collection of coagulation studies( prothrombin time)  URINE SAMPLE COLLECTION What is urine ? Urine is an ultrafiltrate of the blood plasma and fluid created in the kidney and stored in the urinary bladder. It is a waste product and it can give us a wealth of information! Many metabolic diseases can be detected and monitored via the urine. Urine is mostly water with dissolved metabolites  URINE SAMPLE COLLECTION METHOD. Urine Specimen Types Include: First Morning Urine: very first urine voided when waking up after sleep, since it has been retained and incubating in the bladder for 6-8 hours and is the most concentrated specimen Advantage : ideal for testing for protein or to confirm proteinuria red blood cells, white blood cells, and casts that may be present will be more stable. NB: The easiest and most common type of preservation is refrigeration of the urine specimen at 4-6 degrees Celsius within 2 hours of collection if the specimen is not able to be tested right away. Random Urine Specimen: This type of urine specimen can be collected at any time, whether day or night No prior patient preparation Easy and convenient Good for routine screening  Catheterized Urine: Obtained using a sterile, flexible tube catheter, which is inserted into the urethra and into the bladder Urine flows into the bladder by gravity and is collected in a plastic reservoir bag Requires healthcare personnel to perform UTIs are common in catheterized patients, so these are often sent for bacterial culture SAMPLE REJECTION Sample Rejection criteria for clinical samples Inappropriate transport (transport temperature, light exposure, delayed transport time Misidentification (unlabeled, mislabeled or mismatched samples) Improper container or tube Insufficient specimen volume (inappropriate blood/anticoagulant ratio) Incorrect preservation, storage Lipemic specimen Hemolyzed specimen Clotted samples with fibrin.