Laboratory Findings in Parkinson's Disease
There are no specific laboratory abnormalities that diagnose Parkinson's disease—the diagnosis is entirely clinical, based on motor examination findings of bradykinesia plus resting tremor or rigidity. 1, 2
Standard Laboratory Testing
Complete blood count, glucose, electrolytes, kidney function, and liver enzymes are obtained to exclude other causes of parkinsonism, not to diagnose Parkinson's disease itself. These tests are typically normal in Parkinson's disease patients. 3
Routine laboratory studies serve only to rule out alternative diagnoses such as metabolic disorders, infections, or electrolyte disturbances that can mimic parkinsonian symptoms. 3
Age-Specific Laboratory Workup
For Patients Under 50 Years
Measure serum ceruloplasmin and 24-hour urinary copper excretion to exclude Wilson's disease, as this treatable condition can present with parkinsonism and must not be missed. 1
Perform slit-lamp examination for Kayser-Fleischer rings as part of the Wilson's disease screening protocol. 1
Check thyroid function tests (TSH, free T4) to rule out hyperthyroidism as a reversible cause of movement symptoms. 1
Assess calcium-phosphorus metabolism to detect intracranial calcifications that may produce parkinsonian features. 1
Measure serum bilirubin to identify remote history of kernicterus, which can cause basal ganglia injury presenting as parkinsonism. 1
Cerebrospinal Fluid Analysis
CSF examination is not diagnostic for Parkinson's disease but may be performed to exclude infectious or inflammatory causes of parkinsonism when the clinical picture is atypical. 3
CSF protein and cell counts are typically normal in Parkinson's disease, unlike in conditions such as Guillain-Barré syndrome where albumino-cytological dissociation occurs. 3
Emerging Biomarkers (Not Yet Standard Practice)
Cerebrospinal fluid and serum tests for α-synuclein and DJ-1 are under investigation but are not currently used in routine clinical diagnosis. 4
Protein panels and autoantibody testing have shown promise in research settings but lack validation for widespread clinical use. 5
A 5-gene panel has demonstrated high specificity and sensitivity in research studies distinguishing early Parkinson's disease from controls, but genetic testing is not part of standard diagnostic workup unless atypical features suggest a genetic form. 5
Critical Diagnostic Pitfall
The absence of laboratory abnormalities does not exclude Parkinson's disease—in fact, normal laboratory results are expected. The diagnosis rests on clinical examination demonstrating bradykinesia with either resting tremor, rigidity, or both. 1, 2
Do not delay diagnosis waiting for laboratory confirmation, as no such confirmatory test exists. If clinical features are present and secondary causes have been excluded, proceed with clinical diagnosis and consider I-123 ioflupane SPECT/CT (DaTscan) if uncertainty remains. 1, 6