By Dr Ananya Mandal, MD
Diagnosis of acute lymphoblastic leukemia is based on laboratory and pathological tests. The first test is usually blood tests. If this indicates abnormalities, further tests are ordered.
First a complete blood count is prescribed. Anemia is commonly detected with haemoglobin levels usually less than 5g/dl. In addition there is thrombocytopenia of varying degrees. This means there is a low platelet count.
White blood cell (WBC) count is usually high but may be normal or low. The number of neutrophils is usually low.
When a small sample of blood is smeared onto a glass slide and examined under the microscope there may be presence of blast cells. The blood smear may be normal if the blast cells are confined to the bone marrow.
Blood clotting is tested by checking elevated prothrombin time, reduced fibrinogen level and the presence of fibrin degradation products.
Lactic dehydrogenase levels may be raised in blood. In addition due to increased number of cell death and formation there may be raised uric acid levels.
Liver and renal function is checked especially before administering chemotherapy. In case of infections blood cultures and other appropriate tests may be prescribed.
Bone marrow biopsy
In case of an abnormal blood test, bone marrow biopsy is prescribed. The biopsy involves taking a sample of bone marrow using a syringe. The needle is pierced into the hip bone commonly and a sample is drawn.
The procedure is painful and performed under a local anesthetic. The procedure takes around 15 minutes to complete and is performed on an outpatient basis.
The sample of bone marrow is checked for cancerous cells and abnormal cells. The cells are also checked to see the type of leukemia.
Lymph node biopsy
Biopsy of the swollen lymph nodes are sometimes performed to check on the spread and to distinguish the type of leukemia from other blood cancers like lymphomas.
This involves identifying the genetic blueprints of the cancer cells. The leukemia cells atypical genetic makeup can be identified using these tests. Identifications of the genetic abnormalities helps in determining treatment.
Cytogenetics may show hyperploidy. This means part of one chromosome may be replaced by part of another. This is called translocation.
Common translocations include:-
t(12;21) – this is the most common translocation in childhood ALL seen in 30% cases. It results in the TEL-AML fusion gene.
t(4;11) – this results in the MLL-AF4 fusion gene.
t(9;22) – this is called the Philadelphia chromosome and is seen in 15-30% of patients (commonly in adults)
t(1;19) – this is associated with pre-B ALL and forms E2A-PBX fusion gene.
Cytogenetics also involves assessment of bcr-abl (oncoprotein) by polymerase chain reaction (PCR). It helps identify those patients in whom ALL begins as the lymphoblastic phase of chronic myeloid leukaemia (CML).
CT scan and imaging studies
Those with ALL may need to undergo imaging studies like MRI scans and CT scans to check for spread to major organs like heart, lungs, brain and liver. If there is enlargement of the testes an ultrasound of the testes is ordered.
Lumbar puncture involves taking a small sample of cerebrospinal fluid from the spinal column and checking for presence of abnormal cancer cells. This may be positive in patients in whom the cancer has spread to the central nervous system.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)