Module 4Analytic Phase of Laboratory

Testing

Analytical PhaseO It may be surprising, but current

technology has resulted in the analytical phase now having the least error of the 3 phases of laboratory testing

O Current methods and equipment used to generate test results have a high degree ofO Accuracy

=Correctness – how closely the measurement approaches the true value of the substance being analyzed (analyte)

O Precision=Reproducibility – how closely together are

results from measurements of the same substance in the same sample

Which test is precise, which test is accurate?

Test is neither precise nor accurate

Test is precise but not accurate

Test is precise and accurate

Precision, Accuracy or Both?

O Years ago, it was often said that precision was more important than accuracy in lab testing

O Why? O A lab test which is precise but not

accurate may still be clinically useful if the data is used to follow trends or if the lab has properly set its own reference or normal range

O Presently, most common laboratory tests are both accurate and precise

AutomationO Many laboratory tests are performed on

automated instruments.O Automation and information technology are

widely used to minimize the degree to which manual techniques need to be employed in many testing situations

O There are a number reasons for this trend including:O Advances in technology O The continuing shortage of allied

healthcare personnel entering the field of laboratory medicine

Automated Medical LaboratoryPhoto by – GÜliz A. Barkan, MD

Case Scenario 1O A 32-year old man presents with a 3

week history of fatigue. On physical exam he appears pale and has scattered petechiae.

O His physician begins a diagnostic evaluation: he orders, among other tests, a CBC with differential

Case Scenario 1CBC with diff results

WBC 1.0 L [4.0-10.0] k/ul RBC 2.04 L [3.60-5.50] m/ul Hgb 7.4 L [12.0-16.0] gm/dl Hct 22.2 L [34.0-51.0] % MCV 85 [85-95] flMCH 28.3 [28.0-32.0] pgMCHC 33.3 [32.0-36.0] gm/dl RDW 16.6 H [11.0-15.0] % Plt Count 7 LL [150-400] k/ul Diff Type ManualBlasts % 20Blasts 0.2Gran 20 L [45-70] % Gran # 0.2 L [2.0-7.0] k/mm3 Lymph 45 [20-45] %Lymph # 0.45 [1.0-4.0] k/mm3 Mono 15 [0-10] %Mono # 0.15 [0.0-1.0] k/mm3 Eo 0.0 [0-7] % Eo # 0 [0.0-0.7] k/mm3 Baso 0 [0-2] % Baso # 0.0 [0.0-0.2] k/mm3

Case Scenario 1

O Define “manual differential”.O Why was it done in lieu of an

“automated differential”?

Case Scenario 1Discussion

O Initial specimen analysis was performed by the automated instrument

Photo by Theresa Kristopaitis, MD

Recall the color of the collection tube caps for a CBC?

Case Scenario 1Discussion

O Data generated by the instrument that are not acceptable based on defined criteria are “flagged” to alert the technologist that further investigation is requiredO In this case the marked leukopenia,

thrombocytopenia and anemia resulted in the “flag”

Case Scenario 1“flagged” result

Photos by Theresa Kristopaitis, MD

Automated CBC report

Case Scenario 1Discussion

O The results from the automated count are reviewed by the laboratory technologist

O A manual slide review is performed

Stained Peripheral Blood Smear

Manual Cell Counter

Photos by Theresa Kristopaitis, MD

CBC with manualdifferential reported

Photo byTheresa Kristopaitis,MD

Despite Advances in Automated Laboratory Techniques…

O Some laboratory tests are still performed manually or have manual components

O Hematology (as the case illustrated), microbiology and fluid labs employ medical laboratory technologists who are well-trained in microscopic analyses

O In addition, staff techniques in pipetting, vortexing or staining may affect lab results (remember your days in chemistry lab!)

Gram stain reagents used byMicrobiology Lab Technologiststo prepare smears

Gram stain of a positive blood cultureWhat is your interpretation?

Photos by Theresa Kristopaitis, MD

Gram Positive Cocci in Clusters

Lab Testing is Highly Regulated

O It is critical that clinical laboratory staff adhere to:O A multitude of rigorous accreditation and

regulatory requirements such as:O Use of standard operating proceduresO Appropriate performance of quality control

measurementsO Instrument calibration schedulesO Instrument preventative maintenance schedulesO Participation in external reviews of analyte

testing (proficiency testing)

These measures help ensure the quality of the process during the analytical phase of patient testing

O Proceed to Module 5 “Post Analytic Phase of Laboratory Testing”