Blood Markers for Paraneoplastic Syndrome
Test for neuronal antibodies (onconeural and cell-surface antibodies) in both serum AND CSF, not traditional tumor markers, as the latter are not recommended for paraneoplastic syndrome diagnosis. 1, 2
Key Blood Tests to Order
Neuronal Antibody Panel (Serum)
The critical blood markers are neuronal autoantibodies, which should be tested in serum using:
- Immunohistochemistry for initial screening
- Immunoblot for confirmation of intracellular antigens
- Cell-based assay (CBA) for confirmation of surface antigens 3
Serum is more sensitive for:
- Onconeuronal antibodies (anti-Hu, anti-Yo, anti-Ri, anti-CV2, anti-amphiphysin, anti-Ma1, anti-Ma2)
- LGI1 antibodies
- AQP4 antibodies 1
Most Common Antibodies Found
Based on large screening data, the most frequently detected antibodies are 4:
- Anti-Hu (31.8%) - strongly associated with small cell lung cancer
- Anti-Yo (18.2%) - associated with ovarian and breast cancer
- Anti-CV2 (13.6%)
- Anti-NMDA (9.1%) - associated with ovarian teratoma
CSF Testing is Also Required
You must test CSF in addition to serum because some antibodies are more sensitive in CSF:
- NMDAR antibodies
- GFAP antibodies 1
What NOT to Test
Classical tumor markers (CEA, CA-125, CA 19-9, PSA, AFP, etc.) are NOT recommended for screening or diagnosing paraneoplastic syndromes. 2 These have no role in the diagnostic workup and should not be ordered for this indication.
Critical Caveats
False Negatives
- Testing only serum OR only CSF can miss the diagnosis - both must be tested 5
- Commercial antibody panels don't include all paraneoplastic antibodies - if clinical suspicion remains high despite negative commercial testing, send samples to a research laboratory 5
False Positives
- Risk increases when antibody tests are ordered with low pre-test probability 5
- Low-titer positive results should be interpreted cautiously 5, 4
- Positive results only by immunoblot or CBA (without immunohistochemistry confirmation) should be taken with caution 3
Antibody Titer Matters
Higher antibody titers correlate with presence of cancer - this can help predict malignancy risk 4
When to Order These Tests
Only order neuronal antibody testing when the patient presents with high-risk or intermediate-risk neurological phenotypes 3:
High-risk phenotypes:
- Limbic encephalitis
- Rapidly progressive cerebellar syndrome
- Opsoclonus-myoclonus syndrome
- Subacute sensory neuronopathy
- Lambert-Eaton myasthenic syndrome
Intermediate-risk phenotypes:
- Brainstem encephalitis
- Myelopathy
- Stiff person syndrome
- Retinopathy
Indiscriminate testing decreases diagnostic value - restrict testing to appropriate clinical syndromes 3, 6
Specialist Consultation
90% of positive tests are ordered by neurologists or neuro-oncologists 4 - consider specialist consultation before ordering these specialized panels to improve test utilization and interpretation.