化验 (huà yàn): chemical examination; to do a lab test

The doctor said I need to get a blood test first to see whether my white blood cell count is high, and only then can he decide whether to prescribe antibiotics.

That chemical plant discharged wastewater directly into the river; the environmental protection agency took water samples for chemical testing and found heavy metal levels far above the standard.

She had been feeling thirsty and weak lately, so she went to the hospital for blood and urine tests, and only then did she learn that she had diabetes.

Police collected suspicious powder at the crime scene, sent it to a professional lab for analysis, and confirmed that it was an illegal drug.