Laboratory Testing Indications by Clinical Presentation
Acute Hemorrhagic Stroke
For patients presenting with acute hemorrhagic stroke, immediately obtain blood glucose, complete blood count with platelets, serum electrolytes/renal function, coagulation studies (PT/INR and aPTT), cardiac markers, and oxygen saturation. 1
Essential Initial Tests
- Blood glucose is critical to exclude hypoglycemia mimicking stroke and because hyperglycemia worsens hemorrhagic stroke outcomes 1
- Complete blood count with platelet count identifies thrombocytopenia that may contribute to bleeding or alter management 1
- Coagulation studies (PT/INR and aPTT) detect coagulopathies contributing to hemorrhage 1
- Serum electrolytes and renal function assess imbalances affecting management decisions 1
- Cardiac markers identify concurrent cardiac conditions related to stroke 1
- ECG detects arrhythmias or structural heart disease 1
Conditional Testing
- Hepatic function tests when liver disease or alcohol use is suspected 1
- Toxicology screen for atypical presentations or suspected drug use 1
- Blood alcohol level when intoxication is suspected 1
- Pregnancy test for women of childbearing age 1
- Arterial blood gas when hypoxia or respiratory compromise is present 1
Rhabdomyolysis
For suspected rhabdomyolysis, immediately measure creatine kinase (CK), serum creatinine, complete electrolyte panel including potassium, calcium, phosphorus, and magnesium, and obtain urinalysis to detect myoglobinuria. 2
Core Laboratory Panel
- Creatine kinase (CK) is the primary diagnostic marker; levels >15,000 IU/L indicate severe rhabdomyolysis requiring >6L fluid resuscitation 2
- Serum potassium monitoring is critical as hyperkalemia causes life-threatening cardiac arrhythmias 2
- Urinalysis showing brown color, cloudiness, and blood-positive without RBCs confirms myoglobinuria 2
- Serum creatinine assesses for acute kidney injury, a major complication 2
- Complete electrolyte panel including calcium, phosphorus, and magnesium 2
Additional Testing Based on Context
- Liver function tests (AST, ALT) to assess hepatic involvement and distinguish injury patterns 2
- Coagulation studies to evaluate for disseminated intravascular coagulation 2
- Arterial blood gas to assess metabolic acidosis in severe cases 2
- Cardiac troponin and ECG to rule out cardiac involvement 2
Etiology-Specific Testing
- Medication review to identify causative agents, particularly statins 2
- Toxicology screen when drug-induced rhabdomyolysis is suspected 2
- Genetic testing (RYR1, CACNA1S, CPT2, PYGM) for recurrent episodes, exercise intolerance, or family history of neuromuscular disorders 2
- Viral studies if viral myositis is suspected 2
- Autoimmune markers (ANA, ASMA, ANCA) when autoimmune myositis is considered 2
Critical Timing Considerations
- Repeat CK at 24 hours post-trauma if initial levels are normal but clinical suspicion remains, as CK peaks 24-120 hours after injury due to lymphatic clearance mechanisms 2
Hypereosinophilia and Suspected Myeloid/Lymphoid Neoplasms
For patients with hypereosinophilia, obtain CBC with differential, comprehensive metabolic panel with uric acid and LDH, serum tryptase, vitamin B12, and peripheral blood smear review. 3
Initial Workup
- History focusing on travel, new medications, recurrent infections, and family history of eosinophilia 3
- Physical examination including skin evaluation, hepatosplenomegaly assessment, and signs of immunodeficiency 3
Essential Laboratory Tests
- CBC with differential to quantify eosinophilia and detect other abnormalities (dysplasia, monocytosis, blasts) 3
- Comprehensive metabolic panel with uric acid, LDH, and liver function tests 3
- Serum tryptase is elevated in myeloproliferative variants, particularly PDGFRA fusion gene neoplasms and systemic mastocytosis 3
- Vitamin B12 is commonly elevated in myeloproliferative variants 3
- Peripheral blood smear review for morphologic abnormalities 3
Conditional Testing Based on Clinical Presentation
- Serology for Strongyloides and parasitic infections 3
- Stool ova and parasites with GI PCR 3
- ANCA and ANA testing 3
- Quantitative immunoglobulins including IgE (elevated in allergies, infections, L-HES) 3
- Aspergillus-specific IgE to evaluate for allergic bronchopulmonary aspergillosis 3
- ESR and C-reactive protein 3
Definitive Diagnostic Testing
- Bone marrow aspirate and biopsy with immunohistochemistry (CD117, CD25, tryptase), reticulin/collagen stains 3
- Conventional cytogenetics 3
- FISH and/or nested RT-PCR to detect tyrosine kinase fusion gene rearrangements 3
- Flow cytometry to identify aberrant T-cell populations (CD3-, CD4+, CD7-, CD5+) if L-HES suspected 3
- Next-generation sequencing via myeloid mutation panels when no TK fusion genes detected, to establish clonality 3
Pediatric and Adolescent Psychotic Symptoms
For children and adolescents presenting with psychotic symptoms, perform a thorough pediatric and neurological evaluation with laboratory tests justified by clinical presentation rather than routine screening. 3
Basic Medical Evaluation
- Complete blood count 3
- Serum chemistry studies 3
- Thyroid function tests 3
- Urinalysis 3
- Urine toxicology screen 3
Conditional Testing
- HIV testing when risk factors are present 3
- Chromosomal analysis for clinical features suggesting developmental syndromes (e.g., velocardiofacial syndrome) 3
- Neuroimaging studies when neurological dysfunction is evident 3
- Electroencephalogram for suspected seizure disorders 3
- Neurology consultation when indicated by examination findings 3
Important Caveats
- Laboratory testing should be targeted based on history and physical examination findings, not performed routinely 3
- Studies show that routine medical testing in pediatric psychiatric ED patients rarely changes management; only 3 of 208 patients had abnormalities requiring intervention, all suspected clinically 3
- Urine drug screens rarely impact ED management despite high prevalence of substance abuse in adolescent schizophrenia 3
- Psychotic symptoms persisting >1 week despite documented detoxification suggest primary psychotic disorder rather than substance-induced psychosis 3
Waldenström Macroglobulinemia/Lymphoplasmacytic Lymphoma
For suspected WM/LPL, obtain serum protein electrophoresis, serum quantitative immunoglobulins, serum immunofixation, and perform bone marrow aspirate/biopsy with MYD88 (L265P) mutation testing. 3
Essential Tests
- CBC with differential 3
- Comprehensive metabolic panel including BUN/creatinine, electrolytes, albumin, calcium, liver function tests 3
- Peripheral blood smear examination 3
- Serum protein electrophoresis to identify monoclonal IgM protein 3
- Serum quantitative immunoglobulins 3
- Serum immunofixation electrophoresis to quantify M-protein 3
Definitive Diagnostic Testing
- Unilateral bone marrow aspirate and biopsy to document lymphoplasmacytic cell population 3
- Immunohistochemistry and/or flow cytometry showing sIgM+, CD19+, CD20+, CD22+ profile 3
- MYD88 (L265P) mutation testing via allele-specific PCR (present in >90% of WM cases) 3
- Multiparametric flow cytometry for immunophenotypic characterization 3
Staging and Prognostic Assessment
- CT chest/abdomen/pelvis with IV contrast and/or PET-CT to assess adenopathy, splenomegaly, and extramedullary disease 3
- International Prognostic Scoring System for WM (IPSSWM) for prognostication at first-line treatment 3
Interstitial Cystitis/Bladder Pain Syndrome
For suspected IC/BPS, the basic assessment requires urinalysis and urine culture; cystoscopy and urodynamics are not necessary for uncomplicated presentations. 3
Essential Testing
- Urinalysis 3
- Urine culture to detect clinically significant bacteria not identifiable on dipstick or microscopy 3
- Urine cytology if smoking history or unevaluated microhematuria present, given bladder cancer risk 3
Tests NOT Recommended
- Potassium sensitivity test lacks specificity and sensitivity to change clinical decision-making 3
Conditional Procedures
- Cystoscopy only when diagnosis is uncertain; not required for uncomplicated presentations 3
- Urodynamics only when diagnosis is uncertain 3