Urine Blood / Hemoglobin

A urine dipstick that reads "blood: trace" or "blood: 1+" has found heme, the iron-carrying part of hemoglobin. It has not found red blood cells. Intact red cells, hemoglobin that leaked out of broken red cells, and myoglobin from damaged muscle all turn the pad the same color ². The American Urological Association (AUA) is explicit that a positive dipstick alone does not define microhematuria (blood in urine visible only under a microscope) ¹. A positive blood pad becomes hematuria only after microscopy counts the red cells.

How the dipstick blood pad works

The blood pad is coated with a chemical that changes color when heme touches it, shifting from yellow toward green or blue ². The darker the color, the more heme, which is why results are graded negative, trace, 1+, 2+ and 3+.

Three substances carry heme into urine, and the blood pad reacts to all three ²:

• Intact red blood cells, from bleeding anywhere between the kidneys and the urethra. Intact cells often give a speckled or dotted pattern on the pad, because each cell makes its own small spot of color ².
• Free hemoglobin, released when red cells break apart in the bloodstream (hemolysis), or when red cells burst in <a href="/biomarkers/urine-specific-gravity">very dilute urine</a> after the sample is passed. Free hemoglobin colors the pad evenly ².
• Myoglobin, the oxygen-holding protein of muscle, released when muscle breaks down (rhabdomyolysis) after extreme exertion, heat, crush injury or some drugs ^{2 5}.

The blood pad is sensitive: Simerville and colleagues report sensitivity of 91 to 100% for red cells, with specificity of 65 to 99% ². The pad rarely misses blood that is there, but a fair share of positive pads turn out to have few or no red cells on microscopy.

False positives and false negatives on the blood pad

The vitamin C effect matters for people taking high-dose supplements: a negative blood pad in that setting is less reassuring. If you take high-dose vitamin C, tell the clinician ordering the test; they can decide whether to repeat it. The <a href="/compounds/vitamin-c">vitamin C page</a> covers the supplement itself, and <a href="/learn/urinalysis-explained">urinalysis explained</a> walks through the other pads on the same strip.

Why microscopy confirms blood in urine

Clinicians should define microhematuria as three or more red blood cells per high-power field on microscopic evaluation of a single, properly collected urine specimen.American Urological Association and Society of Urodynamics, Female Pelvic Medicine and Urogenital Reconstruction (AUA/SUFU) Microhematuria Guideline, 2020 ¹

The same guideline says clinicians should not define microhematuria by a positive dipstick alone; a dipstick showing trace blood or more should prompt microscopy of the urine ¹.

Microscopy means a lab technician or an automated analyzer spins the urine down and counts the red cells in a high-power field, one view through the microscope at about 400 times magnification ⁴. The <a href="/biomarkers/urine-rbc-microscopy">urine RBC microscopy page</a> owns the count itself and its cutoffs. Many labs run microscopy automatically (a reflex test) whenever the blood pad is positive, so the count may already be further down your report.

What each microscopy result points to

Once microscopy is back, a positive blood pad points in one of four directions.

A blood-positive dipstick with no red cells on microscopy points away from bleeding and toward free hemoglobin or myoglobin ². Free hemoglobin suggests red cells breaking down in the bloodstream, which a clinician checks with blood tests; the <a href="/learn/cbc-explained">CBC explainer</a> and the <a href="/conditions/anemia">anemia page</a> cover that side. Myoglobin suggests muscle injury, and the setting usually makes that obvious.

Blood plus protein: when the kidney filters are the source

When microscopy shows misshapen red cells or red cell casts (tube-shaped clumps of red cells formed inside the kidney), or when the <a href="/biomarkers/urine-protein-dipstick">urine protein pad</a> or the <a href="/biomarkers/urine-acr">urine albumin-to-creatinine ratio (ACR)</a> is also raised, the blood is more likely leaking through the glomeruli, the kidney's filtering units ³. That moves the follow-up toward kidney tests such as <a href="/biomarkers/egfr">eGFR</a> (estimated glomerular filtration rate) and <a href="/biomarkers/creatinine-serum">serum creatinine</a>, and often toward a nephrologist. The AUA guideline also advises a nephrology referral alongside any urologic workup when these kidney signs are present ¹. <a href="/learn/kidney-function-explained">Kidney function explained</a> and the <a href="/conditions/chronic-kidney-disease">chronic kidney disease page</a> cover what those numbers mean.

Common harmless reasons for a positive blood pad

Several everyday causes put real or apparent blood into a urine sample for a short time. The AUA guideline supports repeating the urinalysis after a temporary cause has passed before starting a full workup in a low-risk person ¹.

• Menstruation: menstrual blood easily gets into the sample. Testing outside the period, or telling the lab, avoids a confusing result ².
• Hard exercise: long runs, intense training and contact sports can cause short-lived blood in urine. The AUA advises repeating the urinalysis once the cause has passed ¹.
• A urinary tract infection: inflamed bladder lining bleeds. The AUA advises treating a documented infection and then repeating the urinalysis to check that the blood has cleared ¹. The <a href="/biomarkers/urine-leukocyte-esterase">leukocyte esterase</a> and <a href="/biomarkers/urine-nitrite">nitrite</a> pads on the same strip help show whether infection is likely. For the bigger picture on urine infections, see the <a href="/topics/infections">infections hub</a>.
• Recent procedures: a catheter, a cystoscopy (a camera look inside the bladder) or a prostate procedure can leave blood in urine for a while.
• Contamination: a sample that was not collected midstream, or a cup with cleaner residue ⁴.

Blood thinners do not explain blood in urine on their own. The AUA guideline says people taking anticoagulant or antiplatelet drugs should be evaluated the same way as people not taking them ¹. Do not stop or change a blood thinner because of a urine result; talk to the clinician who prescribed it.

AUA risk groups and what they mean for next steps

Once microscopy confirms microhematuria, the AUA 2020 guideline sorts people into three risk groups for urinary tract cancer, mostly bladder cancer ¹. Age, smoking and the red cell count drive the tiers because each one raises cancer risk. A pack-year is one pack of cigarettes a day for one year, so 20 cigarettes a day for 15 years is 15 pack-years. Any single high-risk feature puts a person in the high-risk group. Low risk applies only when every low-risk feature is met; any one intermediate feature, with no high-risk feature, makes the group intermediate ¹.

The tiers track how often cancer is actually found. Among people with microhematuria, the AUA estimates urinary tract cancer in about 0 to 0.4% of the low-risk group, 0.2 to 3.1% of the intermediate group and 1.3 to 6.3% of the high-risk group ¹. That gap is why a low-risk person may start with a repeat test while a high-risk person goes straight to imaging and cystoscopy.

For a low-risk person whose repeat urinalysis shows no microhematuria, the AUA guideline does not call for further testing ¹. A low-risk person whose repeat sample still shows 3 or more RBC/HPF moves up to intermediate or high risk and gets the matching evaluation.

Visible blood is a different level of concern

Visible (gross) blood, urine that looks pink, red or brown, carries a much higher rate of cancer than microscopic blood, and the AUA places any history of it in the high-risk group ¹. Visible blood warrants a urologic evaluation even if it happens once and then stops. Beets, rhubarb, some medicines and dehydration can also change urine color; the <a href="/biomarkers/urine-color">urine color page</a> covers those, and a dipstick and microscopy separate dye from real blood.

How the test is done and when to repeat it

• No fasting is needed. The blood pad comes with every standard urinalysis; no separate order is needed.
• A clean-catch midstream sample gives the most reliable result: clean the area, start urinating into the toilet, then collect the middle part of the stream ⁴.
• Avoid testing during a period or within a day or two of very hard exercise if you can, or tell the lab if you cannot.
• Microscopy is often added automatically when the blood pad is positive. If it was not, a clinician can request it on the same or a fresh sample.
• A urinalysis is one of the least expensive lab tests and is often covered by insurance when a clinician orders it; check with your plan.
• For a low-risk person, the AUA guideline frames the repeat as a urinalysis within 6 months; after an obvious temporary cause, a clinician may repeat it sooner ¹.

A single trace result rarely means much on its own. Two or three urinalyses over time tell a clearer story than one, which is the idea behind <a href="/learn/trends-beat-single-readings">why trends beat single readings</a>. For the wider urine panel, see the <a href="/topics/urine">urine topic hub</a> and <a href="/learn/how-to-read-any-lab-result">how to read any lab result</a>.

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