CLINICAL CHEMISTRY

• Clinical Chemistry

  • most automated area of the laboratory
  • Instruments are computerized and designed to perform single and multiple tests from small amounts of specimen
• Areas in Clinical Chemistry

  • General or automated chemistry
  • Electrophoresis
  • Toxicology
  • Immunochemistry
• Sample Collection and Handling

  • tests are performed primarily on SERUM collected in gel barrier tubes, but the serum may also be collected in tubes with red, green, gray, or royal blue stoppers.
  • also performed on plasma, urine, and other body fluids
• Sample Collection and Handling

  • Serum and plasma are obtained by centrifugation, which should be performed within 1 to 2 hours of collection
  • Because many tests are performed on instruments that take photometric readings, differences in the appearance or color of a specimen may adversely affect the test results
• Specimens of concern include:

  • Hemolyzed specimens
  • Icteric specimens
  • Lipemic specimens
• Hemolyzed specimens

  • appear red because of the release of hemoglobin from RBCs
• Icteric specimens

  • appear yellow because of the presence of excess bilirubin
• Lipemic specimens

  • are cloudy because of increased lipids
• Sample Collection and Handling

  • Fasting samples drawn from patients who have not eaten for 8 to 12 hours are preferred.
  • Serum separator tubes contain an inert gel that prevents contamination of the specimen by RBCs or their metabolites.
• Sample Collection and Handling

  • Samples must be allowed to clot fully before centrifugation to ensure complete separation of the cells and serum.
  • Many chemistry tests require special collection and handling procedures, such as chilling and protection from light
• Routine Samples

  • tests that are ordered by the health-care provider to diagnose and monitor a patient’s condition.
  • usually collected early in the morning but can be collected throughout the day during scheduled “sweeps” (collection times) on the floors or from outpatients.
• ASAP Samples

  • “as soon as possible.”
  • The response time for the collection of this test sample is determined by each hospital or clinic and may vary by laboratory tests.
• Stat Samples

  • is to be collected,analyzed, and results reported immediately.
  • highest priority and are usually ordered from the emergency department or for a critically ill patient whose treatment will be determined by the laboratory result.
  • The sample must be delivered to the laboratory promptly and the laboratory personnel notified.
• FASTING SAMPLES

  • the patient must only have refrained from eating and drinking (except water) for 12 hours
  • Drinking water is encouraged to avoid dehydration in the patient, which can affect laboratory results.
• FASTING SAMPLES

  • Test results most critically affected in a nonfasting patient are those for glucose, cholesterol, triglycerides, or lipid profiles.
  • Prolonged fasting increases bilirubin and triglyceride values and markedly decreases glucose levels
• FASTING SAMPLES

  • When a fasting sample is requested, it is the responsibility of the phlebotomist to determine whether the patient has been fasting for the required length of time.
  • If the patient has not, this must be reported to a supervisor or the nurse and noted on the requisition form if the decision is made to collect the sample nonfasting
• TIMED SAMPLES

  • Requisitions are frequently received requesting that blood be drawn at a specific time.• Phlebotomists should arrange their schedules to be available at the specified time and should record the actual time of collection on the requisition and sample tube
• Glucose Tolerance Tests

  • for the diagnosis of diabetes mellitus and gestational diabetes.
  • included the 2-hour postprandial (pp)glucose test and the classic glucose tolerance test (GTT).
• Test Procedure: Fasting Blood, 3-hour test: 0700
• Test Procedure: Patient finishes glucose, 3-hour test: 0800
• Test Procedure: 1-Hour sample, 3-hour test: 0900
• Test Procedure: 2-Hour sample, 3-hour test: 1000
• Test Procedure: 3-Hour sample, 3-hour test: 1100
• GTT Preparation

  • Before the test, patients should be instructed to eat a balanced diet that includes 150 g per day of carbohydrates for 3 days and to fast for 12 hours but not more than 16 hours
• Certain medications can interfere with the test results:

  • Alcohol
  • Anticonvulsants
  • Aspirin
  • Birth control pills
  • Blood pressure medications
  • Corticosteroids
  • Diuretics
  • Estrogen-replacement pills
• GTT Preparation

  • For glucose tolerance tests, the fasting patient should be instructed to abstain from food and drinks including coffee and unsweetened tea, except water, for 12hours but not more than 16 hours before and during the test.
• GTT Preparation

  • Smoking, chewing tobacco, alcohol, sugarless gum, and vigorous exercise should be avoided before and during the test because they stimulate digestion and may cause inaccurate test results.• Note on the requisition form if the patient is chewing gum.
• 2-Hour Oral Glucose Tolerance Test

  • recommended method for the diagnosis of diabetes mellitus.
  • requires the collection of a fasting glucose sample, having the patient drink a 75-gglucose solution within 5 minutes and return for an additional glucose test in 2hours.
  • Diabetes mellitus= ≥200 mg/dL
• One-step method

  • utilizes the same procedure as the diagnostic OGTT used to diagnose diabetes mellitus
  • Normal value: ≤ 140 mg/dL
• Two-step method

  • requires the patient to receive two tests
  • First a 50-g glucose challenge load is administered to the fasting patient and blood collected and tested at1-hour post ingestion.
  • The second test is administered on a different day and consists of either a 75-g OGTT or a 100-g 3-hourOGTT based on institutional protocol and health-careprovider preferences.
• Two-step method (Normal Values)

  • 2-hour 75-g test: 155mg/dL
  • 3-hour 100-g test: 140 mg’dL
• Lactose Tolerance Test

  • evaluates a patient’s ability to digest lactose, a milk sugar.• The enzyme mucosal lactase converts lactose into glucose and galactose.
  • Patients without this enzyme are unable to break down lactose from milk and milk products, which may result in gastrointestinal discomfort and diarrhea.
  • Avoiding milk can reduce the symptoms
• Lactose Tolerance Test

  • The patient is asked to drink a standardized amount of lactose solution based on bodyweight in place of the glucose.
  • A blood collection schedule is similar to a 2-hour GTT.
  • Glucose levels will raise no more than 20mg/dL from the fasting sample result if the patient is lactose intolerant