Laboratory Testing for Sudden Unilateral Numbness
For sudden unilateral numbness, you should immediately order: complete blood count, comprehensive metabolic panel (glucose, renal function, electrolytes), coagulation studies (PT/INR, aPTT), troponin, and lipid profile as initial bloodwork, combined with urgent brain imaging (CT or CTA from aortic arch to vertex) and 12-lead ECG to rule out stroke. 1, 2, 3
Clinical Context Matters
Sudden unilateral numbness is a stroke symptom until proven otherwise, not a polyneuropathy presentation. The guidelines for stroke evaluation differ fundamentally from those for chronic polyneuropathy workup.
Immediate Stroke Protocol Labs
The Canadian and American stroke guidelines are clear and recent (2018-2021) on what to order emergently 1, 2, 3:
Initial bloodwork panel:
- Complete blood count (hematology)
- Comprehensive metabolic panel including:
- Blood glucose (to identify hyperglycemia/hypoglycemia as stroke mimics)
- Renal function (creatinine, eGFR)
- Electrolytes (sodium, potassium abnormalities can mimic stroke)
- Liver function tests
- Coagulation studies (aPTT, INR) - essential before any potential thrombolysis
- Troponin (3% of acute stroke patients have concurrent MI) 2
- Random glucose or HbA1c
Subsequent tests to consider:
What NOT to Order Initially
Do not order polyneuropathy screening tests like vitamin B12, serum protein immunofixation, or methylmalonic acid in the acute setting of sudden unilateral numbness 4. These are appropriate for chronic, bilateral, symmetric "stocking-glove" distribution symptoms that develop over weeks to months, not acute unilateral presentations.
The polyneuropathy guidelines explicitly state they apply to distal symmetric polyneuropathy (DSP), which presents with gradual onset bilateral symptoms 4. Sudden unilateral numbness doesn't fit this pattern.
Risk Stratification Determines Urgency
High-Risk Features (Evaluate Within 24-48 Hours)
If the patient has sudden onset with:
- Motor weakness accompanying numbness
- Facial involvement
- Speech difficulties
- Visual changes
- ABCD² score ≥4
Order all labs stat and arrange immediate vascular imaging 1, 2
Lower Risk (Can Evaluate Within 2 Weeks)
If symptoms have completely resolved and occurred >2 weeks ago, the same lab panel applies but urgency is reduced 1, 3
Additional Testing Based on Initial Results
If initial workup is negative, consider:
Prolonged cardiac monitoring (≥24 hours, ideally 2 weeks) to detect paroxysmal atrial fibrillation - this is Class A evidence for embolic stroke workup 1, 2, 3
ESR and C-reactive protein if the patient is elderly with temporal tenderness, jaw claudication, or scalp pain (giant cell arteritis screening) 5
Lyme serology only if in endemic area or recent travel to endemic regions 6
Hypercoagulability workup only if patient is young (<50 years) without traditional vascular risk factors 2
Common Pitfalls to Avoid
Don't confuse acute with chronic presentations: Ordering B12, SPEP, or genetic testing for sudden unilateral symptoms wastes time and money 4, 7, 8
Don't skip coagulation studies: These are mandatory before considering thrombolysis and must be resulted quickly 1, 3
Don't order extensive autoimmune panels reflexively: The yield is extremely low without specific clinical indicators 7, 8
Don't delay imaging for lab results: Brain and vascular imaging takes priority; labs can be drawn simultaneously 1, 2
The evidence strongly supports a focused, time-sensitive approach prioritizing stroke evaluation over broad neuropathy screening when faced with sudden unilateral numbness 1, 2, 3.