LEC 4: CLINICAL CHEMISTRY

• CLINICAL CHEMISTRY


  most automated area of the laboratory
• CLINICAL CHEMISTRY


  Instruments are computerized and designed to perform single and multiple tests from small amounts of specimens.
• What are the areas in clinical chemistry

  ● General or automated chemistry

  ● Electrophoresis

  ● Toxicology

  ● Immunochemistry
• 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.
• In sample collection and handling also performed on plasma, urine, and other body fluids.
• Serum and plasma are obtained by centrifugation,

  which should be performed within 1 to 2 hours of

  collection.
• 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
• Fasting samples drawn from patients who have not

  eaten for 8 to 12 hours are preferred. (it depends on

  the test)
• Serum separator tubes contain an inert gel that

  prevents contamination of the specimen by RBCs or

  their metabolites.
• 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.
• ROUTINE SAMPLES


  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.”
• ASAP SAMPLES


  The response time for the collection of this test

  sample is determined by each hospital or clinic

  and may vary by laboratory tests.
• ASAP SAMPLES

  SOP standard operating procedure
• STAT SAMPLES (Short turnaround time)


  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.
• STAT SAMPLES (Short turnaround time)

  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
• FASTING SAMPLES


  Drinking water is encouraged to avoid dehydration

  in the patient, which can affect laboratory results.
• FASTING SAMPLES


  Test results most critically affected in a non fasting

  patient are those for glucose, cholesterol,

  triglycerides, or lipid profiles.
• FASTING SAMPLES


  Prolonged fasting increases bilirubin and triglyceride

  values and markedly decreases glucose levels.
• TIMED SAMPLES


  Requisitions are frequently received requesting that

  blood be drawn at a specific time.
• GLUCOSE TOLERANCE TESTS


  for the diagnosis of diabetes mellitus and

  gestational diabetes (pregnant).
• GLUCOSE TOLERANCE TESTS


  included the 2-hour postprandial (pp) glucose test

  and the classic glucose tolerance test (GTT).
• 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
• 2 - HOUR ORAL GLUCOSE TOLERANCE TEST recommended method for the diagnosis of diabetes mellitus.
• 2 - HOUR ORAL GLUCOSE TOLERANCE TEST

  requires the collection of a fasting glucose sample,

  having the patient drink a 75-g glucose solution

  within 5 minutes and return for an additional

  glucose test in 2 hours.
• 2 - HOUR ORAL GLUCOSE TOLERANCE TEST

  Diabetes mellitus= ≥ (greater than) 200

  mg/dL
• ONE-STEP METHOD utilizes the same procedure as the diagnostic OGT T used to diagnose diabetes mellitus
• ONE-STEP METHOD: Normal value: ≤ 140 mg/dL
• TWO-STEP METHOD requires the patient to receive two tests.
• TWO-STEP METHOD First a 50-g glucose challenge load is administered to the fasting patient and blood collected and tested

  at 1-hour postingestion.
• The second test is administered on a different day

  and consists of either a 75-g OGTT or a 100-g

  3-hour OGTT based on institutional protocol and

  health-care provider preferences.
• Normal Values:

  ➢ 2-hour 75-g test: 155 mg/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.