A decreased level of a nutrient in body fluids is best identified using _______.

A decreased level of a nutrient in body fluids is best identified using biochemical assessments. These assessments involve analyzing samples such as blood, urine, or other fluids to measure specific nutrient levels or markers that indicate nutritional status. Biochemical data provides objective and precise information about an individual's nutrient status, allowing for accurate diagnosis of deficiencies or imbalances.

This method is crucial because it reflects the actual amounts of nutrients present in the body, which may not always correlate with dietary intake or clinical signs. For instance, someone might consume adequate nutrients but still exhibit deficiencies at the cellular level; biochemical measurements can reveal this discrepancy.