Complete Blood Count (CBC) Test: What It Measures and When Your Doctor May Order It

A complete blood count, commonly called a CBC, is a routine blood test that measures the cells circulating in your blood, including red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. These measurements help your healthcare provider evaluate your overall health and screen for a wide range of conditions.

This test looks for benzodiazepines in your blood. Benzodiazepines are a class of prescription medications commonly used to treat anxiety, insomnia, seizures, and muscle spasms. Common examples include diazepam (Valium), alprazolam (Xanax), lorazepam (Ativan), and clonazepam (Klonopin). The test uses a screening method with a cutoff of 200 ng/mL, meaning if the level detected is above this threshold, the result is considered positive.

Your doctor may order this test as part of a routine checkup, to investigate symptoms such as fatigue, weakness, fever, unexplained bruising, or unusual bleeding, or to monitor an existing condition such as anemia, infection, or a blood disorder. It is also used to track how treatments like chemotherapy or certain medications are affecting your blood cells.

Your healthcare provider may order this test for several reasons: to monitor if you are taking your prescribed medication as directed (compliance testing), to check for accidental or intentional overdose, to evaluate unexplained symptoms of sedation or confusion, or as part of a broader drug screening panel. It may also be used in emergency settings when a patient presents with symptoms of drug overdose.

The test is performed with a simple blood draw. A healthcare professional will clean the skin on the inside of your elbow, wrap a band around your upper arm, and insert a small needle into a vein to collect a sample into a tube. The procedure usually takes only a few minutes and may cause a brief sting. Pressure and a small bandage are applied afterward, and you can typically return to your normal activities right away.

A healthcare professional will draw a small sample of blood from a vein in your arm using a needle. The blood sample will be collected in a tube and sent to a laboratory for analysis. The test is a screening test, which means it provides a preliminary result. If the initial screen is positive, confirmatory testing may be performed to identify the specific benzodiazepine present.

Your results are reported as numbers compared against reference ranges, and each component tells a different story: red blood cell values can reveal anemia, white blood cell counts may point to infection or inflammation, and platelet levels relate to clotting. Values slightly outside the normal range do not always mean something is wrong, so your provider will interpret them together with your symptoms, medical history, and other test results before recommending any follow-up.

Results are reported as either positive or negative based on the 200 ng/mL cutoff threshold. A negative result means no benzodiazepines were detected, or the level was below the detection threshold. A positive result indicates that benzodiazepines were found in your blood above the cutoff level. However, this test does not indicate the specific amount taken, when it was taken, or whether the level is dangerous. Your healthcare provider will interpret the results in the context of your medical history and symptoms.