Blood in urine levels: what a positive dipstick and red cells on microscopy mean, the causes, and how hematuria is evaluated

The dipstick's blood pad reacts to heme — the iron-containing part of hemoglobin — so it turns positive with intact red cells, with free hemoglobin from red cells that have burst in the bloodstream (hemoglobinuria), and with myoglobin released from damaged muscle (myoglobinuria). The microscope then tells them apart: a positive pad with red cells present is hematuria; a positive pad with no red cells points to hemolysis or muscle breakdown, and the next test is in the blood, not the urine.

Microscopic hematuria is defined as 3 or more red blood cells per high-power field (RBC/hpf) on microscopy of a properly collected specimen. A dipstick alone is not enough to make the diagnosis, and a negative dipstick with red cells seen on microscopy is still hematuria. Gross hematuria — urine that is pink, red or cola-colored — needs only about 1 mL of blood per liter and is evaluated in every case.

The shape of the red cells gives the first clue to origin. Uniform, normal-looking cells come from the bladder, ureters, prostate or urethra; misshapen (dysmorphic) cells, acanthocytes and especially red-cell casts come from the kidney's filters and, together with protein, mean a glomerular disease that is a nephrology problem rather than a urology one.

Anyone who has seen red or brown urine, even once, even if it cleared; anyone with pain on urination, flank pain, a fever or a urinary infection that keeps returning; and anyone with a positive dipstick on a routine urinalysis, which needs a microscopy count to decide whether it is real. People with sickle cell trait, polycystic kidney disease, a family history of kidney disease or hearing loss with kidney problems (Alport syndrome), and those on cyclophosphamide, have specific reasons to check.

The risk-based part of the evaluation depends on age, sex and smoking: men over 40 and women over 50, anyone over 60, smokers with more than ten pack-years, people with occupational exposure to dyes, rubber or leather chemicals, and anyone with gross hematuria are at higher risk of urinary-tract cancer and are investigated more fully. Taking a blood thinner is not an explanation for blood in the urine; anticoagulated patients are evaluated the same way.

Order a complete urinalysis with microscopy; through TestWell it is collected as a walk-in urine sample at a Labcorp patient service center, and the urinalysis with reflex to culture — which adds a culture automatically when infection is suggested — is also offered at Quest. The microscopy count is the part that matters for hematuria, so a dipstick-only test is not a substitute.

Collect a clean-catch midstream sample. Do not collect during menstruation or within a few days of it; wait, or tell the lab, because menstrual blood is the most common false hematuria in women. Avoid vigorous exercise, especially running and contact sports, for 72 hours — exercise hematuria is real and resolves within that time. Note recent sexual intercourse, a catheter or any urologic procedure, a very recent urinary infection, and large doses of vitamin C, which can mask the pad.

Negative on the dipstick and 0–2 red cells per high-power field on microscopy. Three or more RBC/hpf is microscopic hematuria. Labs grade the dipstick trace to 3+ (moderate, large), but the grade only roughly tracks the cell count and the microscopy result is the one to act on.

A number of things turn urine red without blood: beets, blackberries and rhubarb in susceptible people, rifampin, phenazopyridine, nitrofurantoin, senna and some food dyes, and the rare porphyrias — in all of them the dipstick is negative for heme. The pad gives a false positive with povidone-iodine or bleach contamination, bacterial peroxidases in an infected, delayed sample, and menstrual contamination; it reads falsely low with large amounts of vitamin C and in very concentrated or acidic urine where cells crenate.

The common causes, roughly in order: urinary tract infection and cystitis; kidney and ureteral stones; menstrual or other contamination; vigorous exercise; benign prostatic enlargement and prostatitis in men; recent catheterization, cystoscopy or prostate biopsy; and trauma. Sexual activity, a urethral stricture, urethritis from sexually transmitted infections and radiation cystitis also bleed.

Kidney (glomerular) causes announce themselves with dysmorphic red cells, red-cell casts and protein: IgA nephropathy is the most common worldwide, often flaring with a sore throat; thin basement membrane disease is benign and familial; Alport syndrome comes with hearing loss; post-infectious glomerulonephritis, lupus nephritis and vasculitis are the serious, treatable ones. Polycystic kidney disease, sickle cell trait and disease, renal vein thrombosis, and loin pain–hematuria syndrome are non-glomerular kidney sources.

The causes the evaluation is designed not to miss are cancers of the bladder, kidney and upper urinary tract. Painless gross hematuria in a smoker over 60 is bladder cancer until excluded; microscopic hematuria carries a lower but real risk that rises with age, male sex, smoking, chemical exposures and the red-cell count, which is why the AUA stratifies people into low, intermediate and high risk and scales imaging and cystoscopy accordingly.

First, confirm it: a repeat urinalysis with microscopy after any menstruation, exercise or infection has passed. If there was an infection, treat it and repeat the urinalysis about six weeks later — hematuria that persists after a treated infection still needs evaluation. Then check creatinine and eGFR, a urine albumin-to-creatinine ratio and blood pressure; protein, dysmorphic cells or casts alongside the blood mean a nephrology referral rather than a urology one.

For confirmed microscopic hematuria without a kidney pattern, the AUA/SUFU 2020 guideline sets the work-up by risk. Low risk (women under 50, men under 40, fewer than ten pack-years, 3–10 RBC/hpf): repeat the urinalysis in six months or go straight to cystoscopy and a kidney ultrasound. Intermediate risk (women 50–59, men 40–59, 10–30 pack-years, 11–25 RBC/hpf): cystoscopy and a kidney ultrasound. High risk (age 60 or over, more than 30 pack-years, more than 25 RBC/hpf, or any gross hematuria): cystoscopy and CT urography. Urine cytology is not a routine screen but is used for irritative symptoms or persistent hematuria after a negative work-up, and a negative evaluation is followed by a repeat urinalysis in a year.