The diagnostic evaluation is a critical time for these patients. It should provide a complete diagnosis according to the most recent classification system (Swerdlow et al. 2017), assess the presence of and manage any comorbidities, plus identify any predisposition syndrome.

This is essential to ensure accurate diagnosis, accurately classify the subtype of leukaemia, inform prognosis and ensure treatment decisions are evidence-based.

To achieve this the treatment team should perform a series of investigations, outlined below. Pre-treatment laboratory examinations include:

• full blood count and blood film review (note: morphological assessment of the blood film to identify acute promyelocytic leukaemia [APL] should be conducted immediately and the result conveyed to the treating physician)
• urea and creatinine, electrolytes including calcium and phosphate, liver function tests
• uric acid and lactate dehydrogenase
• blood group, antibody screen and red blood cell phenotype
• coagulation studies
• consideration of pharmacogenomic testing (e.g. TPMT and G6PD)
• haemoglobin electrophoresis
• immunoglobulins and T- and B-cell subsets
• for relevant or appropriate groups, pregnancy tests (urine or blood BHCG).

Pre-treatment medical imaging includes a chest x-ray to exclude a mediastinal mass.

Diagnostic laboratory investigations include work-up tests performed on bone marrow and/or trephine biopsy and, at times, also on peripheral blood morphology:

• immunophenotyping, karyotyping and FISH analysis
• molecular genetic analysis
• minimal residual disease (MRD) sample (either PCR-MRD or FLOW or by NGS). Other tests may include:
• DNA microarray (or chromosomal microarray)
• biobanking
• other investigations dictated by clinical trial

Lumbar puncture (LP) is performed to establish if there is any CNS disease. Most paediatric acute leukaemia protocols and adolescent and young adult (AYA) ALL protocols currently recommend that a diagnostic LP should occur before starting systemic chemotherapy. Some patients cannot have an LP before therapy such as those with coagulopathies. Therapy should be performed

with adequate platelet cover and performed by an experienced clinician to reduce the risk of a traumatic tap contaminating the CSF with blasts. To further minimise this complication, intrathecal chemotherapy should be given at the same time as the diagnostic LP.

In children and adolescents, diagnostic tests should be organised to reduce the number of procedures requiring general anaesthesia. For example, use peripheral blood flow cytometry to confirm the immunophenotype to allow central line placement, diagnostic LP and bone marrow (including collection for clinical trial enrolment), all under the same general anaesthetic.

Infection screening

It is important that infection screening is undertaken at diagnosis and before blood product support and definitive treatment. The purpose of this screening is to establish a baseline before administering blood products and to investigate serostatus to herpes family viruses, which may reactivate in immunosuppressed patients.

This screening should include routine serology – HBV, HCV, HIV, HTLV, HSV, VZV, EBV, CMV, syphilis and toxoplasma. For patients born or who have travelled overseas, particularly to tropical regions

or tuberculosis-endemic countries, consultation with infectious diseases should be sought. Other investigations are as clinically indicated and on discussion with the infectious diseases service (e.g. malaria screen, melioidosis serology in patients from Far North Queensland and the Top End of the Northern Territory).

Biobanking

Consent for biobanking of diagnostic material should be sought. In many upfront clinical trials in leukaemia, biobanking is a prerequisite to enrolment.

Measurable/minimal residual disease

An MRD level is a strong and independent predictor of relapse in CAYA acute leukaemia and widely used for risk stratification (Cave et al. 1998; Van Dongen et al. 1998). This requires a diagnostic marrow or peripheral blood specimen to enable identification of leukaemia-specific marker or leukaemia associated immunophenotype.

Clinical trial investigations

Further laboratory tests may be required for enrolment into clinical trials.