What is a good rationale for ordering labs in a patient with dizziness and head trauma, despite normal CBC and CMP results?

Rationale for Laboratory Testing in Dizziness with Head Trauma

Laboratory testing in this patient with dizziness and head trauma serves to identify metabolic, hematologic, or systemic causes that could contribute to her symptoms or complicate management, even when initial results are normal.

Primary Justification for Laboratory Evaluation

• Multisociety guidelines recommend that additional laboratory testing be limited to select patients based on clinical assessment, as nonfocused testing in syncope/presyncope patients does not improve diagnostic yield but increases hospitalization rates and costs 1
• However, this patient's presentation includes both head trauma and recurrent positional dizziness, which creates a distinct clinical scenario requiring evaluation beyond simple syncope workup 1

Specific Indications in This Case

Evaluation of Dizziness Etiology

• Laboratory testing helps exclude non-vestibular causes of dizziness including anemia, electrolyte disturbances, hypoglycemia, and renal dysfunction that could contribute to her symptoms 2, 3
• The normal CBC rules out acute anemia (which could cause dizziness through reduced oxygen delivery) and excludes acute infection that might suggest labyrinthitis 4
• Macrocytosis (MCV 100 fL) without anemia warrants attention as it may indicate B12 deficiency, folate deficiency, or medication effects (particularly relevant given her multiple comorbidities), which can contribute to neurologic symptoms including dizziness 2

Assessment of Metabolic Contributors

• Normal comprehensive metabolic panel excludes hypoglycemia, electrolyte abnormalities, and uremia as contributors to her altered mental status and dizziness 1
• Electrolyte disturbances can exacerbate cerebral edema in the setting of head trauma, making their assessment clinically relevant 5
• Renal function assessment (eGFR 72 mL/min/1.73 m²) is appropriate for her age and helps guide potential medication adjustments or contrast decisions if imaging becomes necessary 1

Risk Stratification for Head Trauma

• Patients on anticoagulants or with coagulopathy are at increased risk for intracranial bleeding after head trauma, making baseline hematologic assessment critical 1
• While this patient's platelet count and coagulation status appear normal, baseline values are essential for comparison if neurologic deterioration occurs 1
• Studies show that patients with syncope and head trauma have a 5-6.4% yield of acute CT abnormalities, nearly all with external evidence of trauma (which this patient has) 1

Orthostatic Hypotension Evaluation

• Her orthostatic vital signs showed significant variability (lying 127/73 to repeat standing 106/68), with associated dizziness during positional changes 1, 6
• Laboratory evaluation helps identify contributing factors such as dehydration (elevated BUN/Cr ratio), anemia, or electrolyte abnormalities that could worsen orthostatic symptoms 6
• Normal albumin and protein levels indicate adequate nutritional status, which is relevant for fluid balance and orthostatic tolerance 6

Clinical Context and Decision-Making

When Labs Add Value Despite Normal Results

• Normal laboratory results provide reassurance that metabolic derangements are not contributing to her symptoms, allowing focus on vestibular and traumatic etiologies 1, 2
• The combination of head trauma, positional dizziness, and multiple comorbidities (COPD, rheumatoid arthritis, depression) creates a complex clinical picture where baseline laboratory values inform management decisions 7, 3
• Post-concussive dizziness has multiple potential etiologies including benign paroxysmal positional vertigo (BPPV), labyrinthine concussion, and central vestibular dysfunction, and laboratory testing helps exclude systemic contributors 2, 7

Important Caveats

• Nonfocused laboratory testing should not delay appropriate imaging when head trauma with red flags is present 1
• This patient declined EMS transport and signed AMA, making documentation of baseline laboratory values particularly important for medicolegal purposes and future care continuity 1
• The macrocytosis finding, while not causing acute symptoms, requires follow-up to exclude B12 deficiency which can cause neurologic symptoms including balance disturbances 2

Pitfalls to Avoid

• Do not use laboratory testing as a substitute for appropriate neuroimaging when head trauma with concerning features is present 1
• Recognize that normal labs do not exclude serious intracranial pathology - her "golf ball-sized bump" and periorbital bruising indicate significant trauma force 1
• Orthostatic vital signs showing positional dizziness with BP variability warrant cardiac evaluation (ECG was recommended but deferred), not just laboratory assessment 1, 6
• Post-traumatic dizziness frequently has both peripheral and central components that laboratory testing cannot identify, requiring vestibular evaluation 2, 7, 3