What is the recommended lab routine for a patient presenting to the emergency unit with acute conditions, considering various demographics and past medical histories, such as elderly individuals or those with a history of diabetes?

Emergency Department Laboratory Testing Recommendations by Clinical Presentation

The laboratory workup in the emergency department should be guided by clinical presentation and history rather than routine blanket testing, as most abnormalities are predicted by careful clinical assessment. 1

General Principles

• History and physical examination predict the majority of laboratory abnormalities, making targeted testing more cost-effective than routine panels 1
• Laboratory testing should be reserved for patients with specific clinical indicators rather than applied universally 1
• Point-of-care glucose testing should be performed immediately in all patients with altered mental status or suspected metabolic emergencies 1, 2

Seizure Presentations

First-Time Seizure (Returned to Baseline)

For otherwise healthy adults with new-onset seizure who have returned to baseline neurologic status, routine extensive laboratory testing is of very low yield. 1

Essential tests:

• Serum glucose - hypoglycemia is the most common unsuspected abnormality, though rare (1-2 cases per 100-250 patients) 1, 3
• Serum sodium - hyponatremia is the second most common finding, usually predicted by history 1, 3
• Pregnancy test for all women of childbearing age - affects disposition and antiepileptic drug selection 1, 3

Not routinely indicated:

• Calcium, magnesium, phosphate levels have no prospective evidence supporting routine use in otherwise healthy patients 1
• Consider calcium only in patients with known cancer or renal failure 3
• Consider magnesium only in suspected alcohol-related seizures 3

Status Epilepticus

Patients in status epilepticus require comprehensive immediate laboratory evaluation to identify treatable causes and guide aggressive management. 2

Immediate essential tests:

• Blood glucose (point-of-care) 2
• Complete blood count 2
• Basic metabolic panel (electrolytes, renal function) 2
• Serum sodium 2
• Antiepileptic drug levels in patients with known epilepsy 2

Additional tests based on presentation:

• Arterial blood gas if respiratory compromise or suspected metabolic acidosis 2
• Toxicology screening if substance use/withdrawal suspected 2
• Pregnancy test in women of childbearing age 2
• Lumbar puncture if febrile or suspected CNS infection 2

Psychiatric Presentations

For alert, cooperative psychiatric patients with normal vital signs and noncontributory history/physical examination, routine laboratory screening is not indicated. 1

High-risk groups requiring targeted evaluation:

• Elderly patients 1
• Patients with substance abuse history 1
• First-time psychiatric presentation (no prior psychiatric history) 1
• Patients with concurrent medical complaints 1
• Lower socioeconomic status 1

For high-risk patients, consider:

• Glucose 1
• Basic metabolic panel if clinical indicators present 1
• Toxicology screening if substance use suspected 1
• Pregnancy test in women of childbearing age 1

Key caveat: Patients with delirium, abnormal vital signs, altered cognition, or abnormal physical examination require full medical evaluation and are excluded from the "psychiatric clearance" approach 1

Stroke/TIA Presentations

All patients with suspected acute stroke or TIA require immediate comprehensive laboratory and imaging evaluation. 1

Initial bloodwork (all patients):

• Complete blood count 1
• Electrolytes 1
• Coagulation studies (aPTT, INR) 1
• Renal function (creatinine, eGFR) 1
• Random glucose 1
• Troponin 1

Subsequent tests (during encounter or outpatient):

• Lipid profile (fasting or non-fasting) 1
• HbA1c or 75g oral glucose tolerance test for diabetes screening 1

Essential non-laboratory tests:

• 12-lead ECG (all patients) 1
• ECG monitoring >24 hours for embolic stroke to detect paroxysmal atrial fibrillation 1

Diabetic Emergencies (DKA/HHS)

Immediate comprehensive laboratory evaluation is essential for all suspected hyperglycemic crises. 1

STAT laboratory tests:

• Plasma glucose 1
• Complete blood count with differential 1
• Electrolytes (with corrected sodium for hyperglycemia: add 1.6 mEq/L for each 100 mg/dL glucose elevation) 1
• Blood urea nitrogen 1
• Creatinine 1
• Chemistry profile 1
• Urinalysis 1

Monitoring during treatment:

• Blood draws every 2-4 hours for glucose, electrolytes, BUN, creatinine, osmolality, venous pH 1
• Venous pH preferred over repeat arterial blood gases (venous pH ~0.03 lower than arterial) 1
• Beta-hydroxybutyrate preferred over nitroprusside method for ketone monitoring 1

Suspected Infection/Sepsis

For patients with suspected infection requiring hospital admission, coagulation studies provide independent prognostic information beyond routine testing. 4

Recommended panel:

• Complete blood count with differential 4
• Basic metabolic panel 4
• International normalized ratio (INR) - elevated INR associated with 2.9-fold increased mortality odds 4
• Partial thromboplastin time (PTT) 4
• Platelet count - thrombocytopenia (<150,000/μL) associated with 2.0-fold increased mortality odds 4

Important caveat: Exclude patients on oral anticoagulants or who received heparin from prognostic interpretation 4

Crush Injury/Rhabdomyolysis

Point-of-care testing is lifesaving when standard laboratory infrastructure is unavailable or overwhelmed. 1

Essential monitoring:

• Electrolytes (especially potassium) 1
• Creatinine 1
• Creatine kinase 1
• Acid-base status 1
• Lactate 1
• Blood urea nitrogen 1

Critical consideration: Point-of-care devices (e.g., iStat) have narrow operational temperature range (16-30°C) and require temperature-controlled containers in extreme conditions 1

Elderly Patients

Elderly patients presenting with any acute condition warrant lower threshold for laboratory evaluation due to atypical presentations and higher risk of occult abnormalities. 1

Patients with Diabetes History

Diabetic patients require glucose monitoring regardless of presenting complaint, as both hypoglycemia and hyperglycemia can precipitate diverse acute presentations. 1, 3

• Point-of-care glucose should be checked immediately 1
• Consider HbA1c if diabetes control status unknown 1
• Lower threshold for comprehensive metabolic panel 1

Common Pitfalls to Avoid

• Do not rely on routine CBC for fever workup - WBC and differential lack specificity to distinguish bacterial from viral infections and lack sensitivity to correlate with disease severity 5
• Do not use INR in isolation to assess bleeding risk in liver disease - INR reflects protein synthetic dysfunction but poorly predicts bleeding 6
• Do not order extensive panels on healthy patients with isolated complaints - history and physical examination predict most abnormalities 1
• Do not skip glucose testing in altered mental status - it is immediately treatable and potentially life-threatening 1, 2
• Do not forget pregnancy testing in women of childbearing age - affects management across multiple presentations 1, 2, 3