These exams are used to predict the likelihood of a positive response by the patient to a shunting procedure. Though there is no way to accurately predict how an individual patient will respond, many doctors find the following tests helpful for their diagnosing.

Lumbar Puncture or Spinal Tap is an invasive diagnostic test that allows CSF to be removed for examination and the pressure of the spinal column to be measured. Typically about 40 - 50 ml (about 3 tablespoons) of CSF is removed to see if any of the symptoms of NPH are relieved.

Generally, there is a response to the gait disturbance within about 6 hours, so the patient should expect to be re-examined the same day. Improvement of symptoms following a lumbar puncture is potentially indicative of a positive response to shunting. If a patient fails to respond it does not mean they do not have NPH but these patients do require further testing such as a CSF drainage test.

External CSF Drainage is an alternative to lumbar puncture and should be performed if the patient fails to respond to a "tap test". There may be a need for more CSF to be removed or more time may be required to demonstrate a response. Many Consultants will omit the "tap test" and instead perform a CSF drainage test as this is more accurate at predicting whether or not someone is likely to respond to treatment for NPH. This procedure requires hospitalization for 3 to 5 days, so that CSF can be drained. The CSF drainage is often done through a device called a lumbar drain. This is a tube in the lower back that is inserted under local anaesthetic that passes into the spinal fluid that surrounds the spinal nerves. An alternative way of draining the fluid is via a ventricular access device. This is a tube that passes directly into the ventricle of the brain through a small hole in the skull that is connected to a hollow plastic chamber (known as a reservoir) that lies under the skin of the scalp just behind the hairline; a small butterfly needle can be passed into this reservoir to drain the fluid. The ventricular access device (which is sometimes referred to as an Ommaya Reservoir) can be inserted either under local or general anaesthetic. The choice of method of CSF drainage will be discussed with your surgeon. Once the fluid is drained, testing of gait and memory function is repeated to see if there is any evidence of improvement. A positive response suggests a high chance of responding to treatment of NPH.

CSF Outflow Resistance Measurement. This is a more involved test that determines the capacity of the body to absorb excess CSF. The test is done through either a lumbar puncture or by needles placed in a ventricular access device. This test is often combined with the CSF drainage test and both tests can be performed simultaneously. The test involves infusion of artificial spinal fluid or sterile saline. Specialized laboratory equipment then determines the body's absorption capacity - sometimes called "outflow resistance". If the outflow resistance is abnormally high, there is a good chance that the patient will improve with shunt surgery. A low test does not completely rule out a response to a shunt, in this case a CSF drainage test may be required.

Although currently there is no strict algorithm, definitive test, or gold ut a response to a shunt, in this case a CSF drainage test may be required.standard for predicting with certainty the existence of NPH, improvement has been recognized in patients with varying duration and significance of symptoms. Consequently a medical evaluation of all potential NPH patients is worthwhile.