HPF stands for “high power field” and refers to the view through a microscope at high magnification. When you see HPF on a urine test report, it tells you how many of a specific cell type (red blood cells, white blood cells, or other elements) were visible in a single microscopic field. It’s the standard unit labs use to report what they find when they examine your urine under a microscope.
How the Microscopic Exam Works
A standard urinalysis has two parts: a dipstick test that checks for chemical markers, and a microscopic exam where a lab technician looks at your urine sample through a microscope. For the microscopic portion, the lab takes about 10 to 15 milliliters of urine and spins it in a centrifuge at low speed for 5 to 10 minutes. This concentrates cells, crystals, and other particles into a small pellet at the bottom of the tube. A drop of that concentrated sediment is placed on a slide and examined.
The technician then looks at this slide under high magnification and counts what they see in a single field of view. That single circle of visibility is one “high power field.” Your results are reported as a count per HPF, such as “5 RBC/HPF” or “3 WBC/HPF.” Some elements, like casts (tube-shaped protein structures), are larger and easier to spot at lower magnification, so they’re reported per low power field (LPF) instead.
Red Blood Cells Per HPF
Red blood cells in urine (called hematuria) are one of the most important things the microscopic exam looks for. Normal limits range from 0 to 2 RBC/HPF in men and 0 to 5 RBC/HPF in women. The American Urological Association defines microhematuria as more than 3 red blood cells per high power field on a properly collected specimen. That threshold is the point where further evaluation is recommended.
Labs typically report red blood cell counts in ranges: 0 to 3, 4 to 10, 11 to 25, 26 to 50, more than 50, or gross hematuria (blood visible to the naked eye). If your results come back above 3 RBC/HPF on two out of three separate urine tests, guidelines recommend a urologic evaluation. Red blood cells in urine can signal kidney disease, a blood disorder, bladder cancer, kidney stones, or other conditions. Many causes turn out to be benign, but the finding warrants investigation, especially if it persists.
White Blood Cells Per HPF
White blood cells in urine suggest inflammation or infection somewhere in the urinary tract. The key threshold here is 5 WBC/HPF. Counts at or below 5 per high power field reasonably rule out a urinary tract infection in most patients. Counts above 5 WBC/HPF are considered a positive finding and point toward a possible UTI or other inflammatory condition.
White blood cells can also show up in urine because of kidney infections, sexually transmitted infections, or inflammation from kidney stones. A high white blood cell count alone doesn’t confirm infection. Labs usually look for bacteria in the sample as well, and your doctor may order a urine culture to identify the specific organism if infection is suspected.
Epithelial Cells Per HPF
Three types of epithelial cells can appear in urine: squamous cells, transitional cells, and renal tubular cells. The type matters more than the count.
Squamous epithelial cells are the most common finding, and they usually mean the sample was contaminated during collection. These cells come from the skin around the genital area, not the urinary tract itself. If your report shows a large number of squamous epithelial cells, it typically means the clean catch technique wasn’t thorough enough, and the test may need to be repeated.
Renal tubular epithelial cells are a different story. These originate in the kidneys and can indicate kidney damage or disease when present in significant numbers. Transitional cells line the bladder and ureters, and small numbers are normal, but elevated counts can warrant further evaluation.
Casts Per LPF
Casts are tube-shaped protein structures that form inside the tiny tubules of the kidney and get flushed out in urine. Because they’re larger than individual cells, they’re counted under low power magnification (LPF) rather than HPF. Their presence, and especially their type, can reveal what’s happening inside the kidneys.
Hyaline casts (made of pure protein) can appear after strenuous exercise or dehydration and are often harmless. Granular casts suggest more significant kidney involvement. White blood cell casts point to kidney infection or inflammation, while red blood cell casts indicate bleeding within the kidney itself, which narrows the diagnostic picture considerably.
What Your Results Mean in Practice
When you see HPF on your urine report, focus on whether the numbers fall above or below the key thresholds: more than 3 RBC/HPF is considered abnormal, more than 5 WBC/HPF suggests possible infection or inflammation, and the presence of renal tubular epithelial cells or certain types of casts points to kidney involvement. A single slightly elevated result doesn’t always indicate a problem. Factors like vigorous exercise, menstruation, dehydration, or improper sample collection can temporarily skew results.
The microscopic exam is a screening tool. Abnormal findings per HPF tell your doctor where to look next, whether that’s a urine culture, imaging of the kidneys and bladder, or a referral to a specialist. Normal findings are equally useful because a clean microscopic exam rules out many conditions quickly and cheaply.