What blood work is recommended for a patient presenting with dizziness?

Blood Work for Dizziness Evaluation

For patients presenting with dizziness, routine blood work is generally not recommended as the primary diagnostic approach, as it has low diagnostic yield in isolated dizziness without specific risk factors or symptoms suggesting systemic causes. 1, 2

Diagnostic Approach to Dizziness

The evaluation of dizziness should focus on:

1. Timing and triggers rather than quality of symptoms
2. Neurological examination including HINTS (Head-Impulse, Nystagmus, Test of Skew) to differentiate peripheral from central causes
3. Targeted testing based on specific clinical findings

Key Physical Examination Components

• Orthostatic blood pressure measurement
• Dix-Hallpike maneuver for positional vertigo
• Assessment for nystagmus
• Complete neurological examination
• HINTS examination when acute vestibular syndrome is present

When Blood Work May Be Indicated

Blood tests should be ordered selectively based on specific clinical suspicions:

• Complete Blood Count (CBC):

  • When anemia is suspected (pallor, fatigue, history of blood loss)
  • In patients with high-risk features (as anemia was associated with 50% risk of poor outcomes) 3

• Blood Glucose/HbA1c:

  • When diabetic neuropathy is suspected as a cause of disequilibrium
  • In patients with symptoms of hypoglycemia or hyperglycemia

• Electrolytes:

  • When dehydration, medication side effects, or renal disease is suspected
  • In patients taking diuretics or with history of electrolyte abnormalities

Imaging vs. Laboratory Testing

The American College of Radiology notes that imaging has low diagnostic yield in isolated dizziness without neurological deficits (<1% for CT, 4% for MRI) 1. Similarly, laboratory testing plays a limited role in diagnosis for most patients with dizziness 4, 5.

Common Pitfalls to Avoid

• Overreliance on laboratory testing when the history and physical examination are sufficient for diagnosis in 83% of cases where a diagnosis can be made 3
• Failure to perform appropriate positional testing such as Dix-Hallpike maneuver
• Missing red flags for central causes requiring further evaluation:
  • Direction-changing nystagmus without head position changes
  • Downbeating nystagmus on Dix-Hallpike
  • Associated neurological symptoms or signs 2

High-Risk vs. Low-Risk Patients

• High-risk (50% poor outcome): Patients with initial diagnosis of anemia, stroke, or diabetes 3
• Low-risk (2% poor outcome): Patients under 50 years or with peripheral vestibular disease, vasovagal/psychogenic causes, medication effects, or infection 3

Algorithm for Blood Work in Dizziness

1. For isolated dizziness without other symptoms or risk factors: No routine blood work needed
2. For orthostatic dizziness/presyncope: Consider CBC, electrolytes, renal function
3. For patients with diabetes or risk factors: Check blood glucose/HbA1c
4. For patients on medications that can affect electrolytes: Check electrolytes, renal function
5. For patients with suspected anemia: Order CBC

Remember that the cause of dizziness remains unknown in approximately 37% of cases even after evaluation 3, and diagnostic testing should be targeted rather than routine.