Wondered what happens behind the lab reports?

Hematology is a specialty which deals with disorders of blood, which can include diverse groups of problems, ranging from nutritional deficiencies to malignancies. Complete blood count (CBC) is usually the first laboratory test which helps to know when a hematological condition is suspected.

A peripheral blood smear (PS) made from the sample received for CBC/ PS is carefully analyzed under microscope, in correlation with values obtained on CBC and the clinical details. Let me explain further with a scenario where a patient suspected to have blood cancer (acute leukemia) is referred for work up to a hematopathologist.

The CBC and PS reflect some important findings based on which diagnosis of acute leukemia can be clinched. Presence of abnormal cells called “blasts” is the most important clue. The percentage of blasts required is usually >20% (exceptions present). Blasts can be present in other conditions also, so mere presence of blasts does not suffice. Supportive findings in CBC are increased or decreased total leucocyte count (TLC), reduced platelets, hemoglobin. It is important to note that the information on PS may or may not be fully helpful in diagnosis as blast count may be borderline, other conditions mimicking leukemia are also possible. Blasts can also be absent in periphery (aleukemic leukemia).

Based on the findings of CBC and PS, a decision for bone marrow aspiration and biopsy (BMA and biopsy) is taken to further conclusively establish the diagnosis. This test is very crucial as samples for additional ancillary tests should also be collected during the process. Failure to collect samples during the procedure might lead to patient undergoing this traumatic procedure again if a need for ancillary test is required later. Equally important is early decision making on proceeding with flowcytometry, cytogenetics and molecular tests as the bone marrow aspiration sample needs to be processed soon. Delay in processing may lead to erroneous or even failed results. RNA based molecular tests also require fresh sample, as RNA is labile and degradation starts soon. Unlike paraffin blocks of biopsy samples, bone marrow aspirate (the liquid) cannot be stored for long.

So what are the ancillary tests we are talking about? Flowcytometry is the first advanced test required in the process of leukemia work up. This test helps in further confirming the diagnosis of acute leukemia, and more importantly telling the type of leukemia based on their origin. Acute leukemias can be myeloid (AML) or lymphoid (ALL, which further can be B- or T-) or mixed/ ambiguous lineage. This is very very important as the management and prognosis of each of them is different. So is flowcytometry an automated test? No. It involves detailed analysis of the cell populations by an experienced hematopathologist trained in flowcytometry. Knowledge of variations, possible pitfalls and quality control are crucial during reporting.

Next important tests which are simultaneously performed are cytogenetics and molecular/ genomic tests. They involve processing on the DNA and RNA extracted from the abnormal blast cells, followed by testing for defining genetic abnormalities. The final classification of acute leukemias is incomplete without these tests. The testing is done in a specialized laboratory and results are correlated with other tests done like CBC, PS, BM morphology and flowcytometry. Valuable information on genetic abnormalities against which targeted therapies are available is obtained from the molecular tests.

Thus, the diagnosis of acute leukemia involves a lot of background work, analysis and correlation of different findings by hematopathologists, before the clinical hematologist can appropriately plan further management. These tests also help in the further course of management to assess the response to therapy and know if the disease is relapsing.

Other hematological malignancies and conditions are also worked up by hematopathologists in a similar manner, integrating crucial results from morphology, flowcytometry, cytogenetic and molecular tests.