The ischemic forearm exercise test is a diagnostic procedure that tests for possible metabolic causes of muscle weakness, cramps and fatigue.
After the patient rests fully for 30 minutes, a blood pressure monitor is placed on their upper arm and they are set up with an intravenous line with saline and heparin. A blood sample is taken for reference purposes. The blood pressure cuff is then inflated and the patient is then given the squeeze bulb and is required to squeeze it themselves every two seconds for a period of two minutes, making sure that their fingers are fully extended between squeezes. After they are finished, the cuff is deflated and blood samples are taken 1, 3, 7, and 9 minutes later.
In all cases, the test is fatiguing and painful. However, most patients can complete the entire two minutes. Even before blood is tested, it's diagnostically relevant if the patient cannot complete the exercise, cannot extend their fingers fully between squeezes, markedly contract their forearm, or do not recover immediately after the blood pressure cuff is released.
After the test, the blood is tested for lactate and ammonia, which should both be above base levels in a normal patient. However, results that are well above base levels show an underlying pathology. If the results are not above base levels, it is likely the patient was not trying hard enough to exercise and the test should be repeated.
The test should not be performed if there is a history of or possibility of alcoholism, hypothyroidism, or an inherited myopathy as the test could cause rhabdomyolysis.