High-power field

A high-power field (HPF), when used in relation to microscopy, references the area visible under the maximum magnification power of the objective being used. Often, this represents a 400-fold magnification when referenced in scientific papers.

The area provides a reference unit, for example in reference ranges for urine tests.

Used for grading of soft tissue tumors: Grading, usually on a scale of I to III, is based on the degree of differentiation, the average number of mitoses per high-power field, cellularity, pleomorphism, and an estimate of the extent of necrosis (presumably a reflection of rate of growth). Mitotic counts and necrosis are the most important predictors.

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