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Body Fluids
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Pending specialist review and validation.
Alpha fetoprotein, or AFP, is a protein that is produced during early development and can also be made by certain tumors. This test measures AFP in cerebrospinal fluid, the clear liquid that cushions and surrounds your brain and spinal cord.
In most older children and adults, AFP in cerebrospinal fluid is expected to be very low. When AFP is present at higher levels, it can point to specific types of tumors that release this protein into the fluid, helping your care team narrow the possible causes of symptoms or imaging findings.
Measuring AFP in cerebrospinal fluid can help diagnose and classify certain central nervous system germ cell tumors, especially those with yolk sac tumor components that tend to produce AFP. It is often ordered together with beta-hCG and with blood tests, then interpreted alongside brain or spine imaging and clinical findings.
Your clinician may also use this test to monitor how a known tumor responds to treatment and to check for recurrence over time. Because other conditions and pre-analytic issues can influence results, AFP in cerebrospinal fluid is only one piece of the overall diagnostic picture.
Your result will be interpreted in the context of your age, symptoms, exam, imaging studies, and related lab tests in both cerebrospinal fluid and blood. A higher AFP level in cerebrospinal fluid can support the diagnosis of a germ cell tumor that produces AFP, but it does not confirm a diagnosis by itself. If the result is unexpectedly elevated or borderline, your clinician may repeat the lumbar puncture, compare with blood AFP, and consider additional imaging.
A result within the expected range lowers the likelihood of tumors that typically secrete AFP, but it does not rule out all tumor types. Technical issues, blood contamination of the sample, and timing relative to recent treatments can affect measurements. Your care team will explain what your particular result means and outline next steps, which may include follow-up testing or referral to neuro-oncology.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Accidental blood mixing during lumbar puncture can carry AFP from the bloodstream into the cerebrospinal fluid sample, potentially causing a falsely higher result.
AFP naturally declines from infancy to later childhood and adulthood, so your age is essential for appropriate interpretation of cerebrospinal fluid results.
Blockages or uneven flow of cerebrospinal fluid can create gradients, so the sampling site and local anatomy may influence measured AFP levels.
Surgery, chemotherapy, or radiation can change tumor secretion patterns over time, so results may shift as treatment progresses or after tumor removal.
Rare antibody interferences and high-dose biotin supplements can affect some immunoassays, potentially leading to inaccurate AFP readings.
Conditions that raise blood AFP, such as active liver disease or pregnancy, can influence cerebrospinal fluid results if there is blood contamination of the sample.
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