What additional diagnostic tests should be ordered for this patient?

Diagnostic Testing Plan

The diagnostic workup should be guided by the specific clinical presentation, with genetic testing as first-tier for neurodevelopmental disorders and structured clinical decision pathways for other conditions based on the most recent professional society guidelines.

For Neurodevelopmental Disorders (Developmental Delay/Intellectual Disability/Autism Spectrum Disorder)

First-Tier Testing (All Patients)

Order chromosomal microarray (CMA) and Fragile X testing immediately for any patient with unexplained developmental delay, intellectual disability, or autism spectrum disorder 1. These are the established first-line genetic tests per the 2020-2021 guidelines from AAP, AACAP, and ACMG.

Additional First-Tier Considerations

• For males with ASD: Fragile X testing is mandatory 1
• For females with ASD or DD: Consider MECP2 sequencing and deletion/duplication analysis 1
• For patients with macrocephaly (head circumference >2.5 SD above mean): Add PTEN testing 1
• For suspected metabolic disease: Order metabolic testing if history and physical examination suggest mitochondrial dysfunction, regression, or specific metabolic indicators 1

Second-Tier Testing (If First-Tier Unrevealing)

Exome sequencing (ES) or whole genome sequencing (WGS) should be ordered as second-tier testing 1. The 2021 ACMG guidelines specifically state ES/WGS should be first- or second-tier for unexplained DD/ID or congenital anomalies 1.

Special Circumstances

• X-linked inheritance pattern suspected: Order X-linked ID panel and high-density X-CMA; consider X-inactivation skewing testing in the mother 1
• Cerebral palsy: CMA or genome sequencing may be diagnostic 1

For Immune-Related Adverse Events (Checkpoint Inhibitor Therapy)

Rheumatologic/Musculoskeletal Symptoms

For new joint pain or suspected inflammatory arthritis 2:

• Inflammatory markers (ESR, CRP) every 4-6 weeks
• Complete rheumatologic examination
• Consider imaging for large joints if grade 2 or higher

For suspected myositis 2:

• Blood tests: CK (primary marker), AST, ALT, LDH, aldolase
• Cardiac evaluation: Troponin to assess myocardial involvement; echocardiogram if indicated
• Inflammatory markers: ESR, CRP
• Grade 2 or higher: Add autoimmune myositis panel, neurologic panel, EMG, MRI of affected proximal limbs
• If diagnosis uncertain: Muscle biopsy
• Consider: Paraneoplastic autoantibody testing for myositis and myasthenia gravis overlap

Hematologic Toxicities

For suspected autoimmune hemolytic anemia 2:

• CBC with peripheral smear looking for hemolysis
• LDH, haptoglobin, bilirubin (direct and indirect), reticulocyte count, free hemoglobin
• Direct agglutinin test (direct and indirect)
• DIC panel (PT/INR)
• Autoimmune serology
• Paroxysmal nocturnal hemoglobinuria screening
• Infectious workup (viral/bacterial including mycoplasma)
• Protein electrophoresis, cryoglobulin analysis
• G6PD level
• If refractory: Bone marrow analysis with cytogenetics, B12, folate, copper, parvovirus, iron, thyroid function

For thrombocytopenia/ITP 3:

• CBC, peripheral smear, reticulocyte count
• HIV, HCV, HBV, H. pylori testing
• Direct antigen test to rule out Evans' syndrome
• Bone marrow evaluation only if other cell lines affected

For Chest Pain/Acute Coronary Syndrome

Use structured clinical decision pathways rather than unstructured assessment 4. The specific testing depends on risk stratification:

Low-Risk Patients

• Serial cardiac troponin (conventional or high-sensitivity) at 0 and 2-3 hours
• If negative with low clinical probability: No further cardiac testing needed

Intermediate-Risk Patients

• Serial troponin measurements
• Consider stress testing or coronary CT angiography based on institutional protocol

High-Risk Patients

• Immediate troponin measurement
• ECG
• Proceed directly to invasive evaluation if indicated

For Suspected Pulmonary Embolism

Follow validated clinical decision rules 5:

Low Clinical Probability

• D-dimer (highly sensitive assay) - if normal, excludes PE
• If D-dimer elevated: MDCT angiography or V/Q scan
• Lower limb compression ultrasound may obviate need for further testing if positive

High Clinical Probability

• Do not order D-dimer - proceed directly to MDCT angiography 5
• If CT negative, consider additional testing given high pretest probability
• Compression ultrasound showing proximal DVT confirms PE without need for pulmonary imaging

Common Pitfalls to Avoid

1. Do not order genetic testing piecemeal - CMA and Fragile X should be ordered together as first-tier for neurodevelopmental disorders, not sequentially
2. Do not skip troponin for myocardial involvement when evaluating checkpoint inhibitor-related myositis - cardiac involvement changes management dramatically 2
3. Do not use D-dimer in high-probability PE - it cannot safely exclude disease even when negative 5
4. Do not order additional neuroimaging or testing in low-yield scenarios without specific clinical indicators - this leads to overdiagnosis 6
5. Test for hepatitis B, C, and TB before initiating DMARD therapy for immune-related arthritis 2