High red blood cells in urine: what your number means

A urine red cell count of 3 or more per high-power field is high, and the medical name for it is microhematuria. Two questions follow. Is the blood real, or did a period, a workout or a rushed sample put it there? And if it is real, does it come from the kidney filters or from somewhere between the kidney's drainage system and the urethra? Hematuria means blood in the urine: visible (gross) when you can see it, microscopic when only the lab can. New to urine tests? How a urinalysis is read walks through every line first.

The American Urological Association and the Society of Urodynamics (AUA/SUFU) define microhematuria as 3 or more red blood cells per high-power field on microscopy of a single, properly collected urine specimen ¹. The lab spins the urine down and counts red cells in several views under a microscope at high magnification (about 400x); a high-power field is one of those views, so 3 RBC/HPF means about 3 red cells in each view ³. MedlinePlus gives a normal result as 4 RBC/HPF or less ⁶, so a count of 3 or 4 can sit inside a lab's printed range yet still meet the AUA definition ¹⁶; treat it as a reason to repeat, not as a diagnosis. Some labs use automated analyzers and report red cells per microlitre (/uL); read that number against the range on your own report. Urine red cells are a separate measurement from the red cell count on a blood test, which our CBC guide covers.

Is 5, 10 or 25 per HPF high?

All three counts are high, since each is 3 or more RBC/HPF. At 3 to 10, whether it comes back on a clean repeat matters most; above 10, the count itself raises the risk group. In higher-risk adults (60 or over, more than 30 pack-years of smoking, or more than 25 RBC/HPF), the guideline bases the work-up on the first properly collected result, because bleeding from the bladder can come and go ¹. Asymptomatic microhematuria turns up in roughly 2% to over 30% of adults, depending on age, sex, smoking and the definition used ².

The harmless reasons it comes back high

A family-medicine review by Sharp and colleagues lists menstruation, vigorous exercise, sexual activity, viral illness and minor trauma as harmless, temporary causes, and advises repeating the urinalysis once they have passed ². Exercise-related blood in the urine usually clears within about 72 hours ². A catheter, a recent urinary procedure or a sample that was not a clean midstream catch can raise the count too.

The reasons that need looking at

Lower-tract causes sit anywhere from the ureters to the urethra: urinary tract infection (UTI) or cystitis, kidney or bladder stones, an enlarged prostate (benign prostatic hyperplasia, BPH) in men, urethritis, and bladder or kidney tumours, whose risk rises with age and smoking. Smoking is the main risk factor for bladder cancer, and about half of bladder cancers in both men and women are attributable to it ⁵.

Kidney (glomerular) causes come from the glomeruli, the tiny filters that clean the blood. IgA nephropathy is the most common primary glomerulonephritis (inflammation of the kidney filters) worldwide and often first shows up as microscopic or visible blood in the urine ⁴. Thin basement membrane disease (an often-inherited, usually harmless thinning of the filter wall) and other forms of glomerulonephritis belong in this group too. Polycystic kidney disease can also cause blood in the urine, though it is not a filter disease. Sickle cell trait and bleeding disorders are less common causes.

Kidney or bladder? What the rest of your urine test shows

The other lines on the same urinalysis are the best clue to where the red cells come from. Abnormal (dysmorphic) red cells, misshapen by squeezing through the filters, along with red cell casts, protein in the urine or a rising creatinine, point to the kidney filters and are grounds for a nephrology referral ¹³. Normal-shaped red cells with no protein point lower down.

If yours points to the kidney, see how kidney function is measured, your creatinine and chronic kidney disease. The leukocyte esterase and dipstick protein lines on the same report sort the infection and kidney rows.

The dipstick reacts to hemoglobin itself, not to whole red cells, so myoglobin from muscle or free hemoglobin can turn it positive with no red cells under the microscope ³. That is why the guideline treats microscopy as the deciding test.

Clinicians should not define microhematuria by positive dipstick testing alone.AUA/SUFU Microhematuria Guideline, 2020 ¹

CalculatoreGFR calculatorIf the pattern points to the kidney, turn your creatinine into an eGFR to see how well the filters are working.Work it out

What happens next: the doctor's steps

1. 1Confirm on microscopyA positive dipstick gets a microscopic urinalysis before any work-up ¹.
2. 2Rule out the harmless causesRepeat after a period, exercise or sex has passed; treat a UTI, then repeat ¹².
3. 3Check for a kidney patternProtein, casts, dysmorphic cells or a rising creatinine go to a kidney specialist (nephrologist) ¹.
4. 4Sort by risk groupAge, sex, smoking, the RBC count and any history of visible blood set how far the bladder and kidneys are imaged ¹.

A pack-year is one pack a day for a year, so 20 a day for 10 years is 10 pack-years. Urothelial cancer is cancer of the lining of the bladder, ureters and kidney drainage system. Cystoscopy is a look inside the bladder with a thin camera; CT urography is a contrast CT scan of the kidneys, ureters and bladder. The age thresholds differ for women and men because bladder cancer is more common in men ¹. Even in the high-risk group, the guideline estimates urothelial cancer in about 1.3% to 6.3% of people ¹.

Can you lower red blood cells in urine?

The count comes down when whatever is causing it is dealt with. That means a clean sample for a fair repeat, treatment for a UTI, management of stones (where drinking more fluid helps prevent new ones), stopping smoking, and blood pressure control when the kidney filters are involved. No supplement has been shown to lower urine red cells. High-dose vitamin C can make the dipstick read falsely negative for blood ³, which hides the finding without changing it; mention any vitamin C supplement before a urine test.

For what the red cell line means at every level, including low and normal results, see the main urine red blood cells page. For the other lines on the report, see the urine topic hub and how to read a full urinalysis, and why a trend beats a single reading explains why the repeat result carries more weight than the first.

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