Dark or Red Urine
Color and the dipstick together split this three ways, and the split is the diagnosis. Red urine with a negative dipstick is pigment from food or a drug and needs nothing. A positive dipstick with red cells visible under the microscope is genuine bleeding. The third combination matters most: a strip reading positive while microscopy finds no cells at all. That means muscle protein or free hemoglobin, and both can injure the kidney.
The pattern on your report
- Dipstick blood Normal Key
- CK Normal Key
- Bilirubin Normal Key
- Hemoglobin Normal Key
Printed as: CK in U/L— The test that identifies muscle as the source, and the reason microscopy matters before anything else.Hemoglobin in g/Lor g/dL— Anemia alongside a positive strip with no red cells points toward red cell destruction.Bilirubin in umol/Lor mg/dL— Dark urine with pale stools points at the liver or bile ducts instead of the kidney.Dipstick blood in dipstick grade— Detects the haem group, not red cells, which is why free hemoglobin and muscle protein both turn it positive.
Why the numbers look like this
The dipstick pad does not detect red cells. It detects the haem group they contain, through a chemical reaction that haem drives regardless of whether it is still inside a cell.
That is why three different things turn it positive. Intact red cells, from bleeding anywhere along the urinary tract. Free hemoglobin, released when red cells are destroyed in the bloodstream. Myoglobin, the closely related muscle protein released when muscle breaks down.
Microscopy separates them, because only the first contains actual cells to see.
The distinction matters because the second and third carry a specific danger. Both proteins are filtered by the kidney in quantity and are toxic to the tubules, so widespread muscle breakdown or a large episode of red cell destruction can cause kidney injury within hours. The urine in those cases is typically brown or cola-colored rather than red.
Pigments work differently again. Beetroot, blackberries, some food dyes and several drugs color the urine without any haem present, so the dipstick stays negative and the finding is cosmetic.
Not being flagged is not the same as normal
The dipstick is sensitive enough to turn positive with a quantity of blood too small to change the color, which is why a normal-looking sample can still be positive and why a positive result in the absence of visible change still needs following up. Working the other way, menstruation contaminates a sample readily and is a frequent cause of a positive result that means nothing about the urinary tract, so timing the sample away from a period avoids an unnecessary investigation.
What else on the report can hide this
Microscopy is the branch point, and it should be requested and not assumed. Red cells present means bleeding; their absence with a positive strip means one of the two proteins.
Creatine kinase settles the muscle question. A markedly raised value with a positive dipstick and no red cells is muscle breakdown, and kidney function and potassium then matter urgently.
If muscle is excluded, the destruction of red cells is the alternative: haptoglobin, LDH, bilirubin and a reticulocyte count identify it, and the blood count will usually already show anemia.
Where red cells are genuinely present, the assessment follows the usual path for blood in the urine, and age determines its urgency.
The pigment causes are settled by history alone. Beetroot within the past day or two, and drugs including rifampicin, nitrofurantoin, senna and some laxatives, each color urine characteristically. Asking is quicker and cheaper than any test.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
Food pigment
Beetroot, blackberries and some dyes, within a day or two. The dipstick is negative because no haem is present.
- Very common
Medication
Rifampicin turns urine orange, nitrofurantoin brown, and senna and some laxatives red or brown. The dipstick stays negative.
- Very common
Concentrated urine
Dark yellow from low fluid intake or the first sample of the day. Clears with drinking.
- Common
Menstrual contamination
A frequent cause of a positive dipstick that means nothing about the urinary tract. Timing the sample away from a period avoids it.
- Common
Genuine bleeding in the urinary tract
Positive dipstick with red cells visible on microscopy. Follows the usual assessment, and age determines its urgency.
- Uncommon
Muscle breakdown
Positive dipstick with no red cells, a markedly raised CK, and brown or cola-colored urine. Kidney injury can follow within hours.
- Uncommon
Red cell destruction
Positive dipstick with no red cells and a normal CK. Haptoglobin, LDH and a reticulocyte count identify it, usually with anemia alongside.
- Uncommon
Bilirubin in the urine
Dark urine with pale stools and yellow eyes. Points at the liver or the bile ducts rather than the kidney.
- Rare
Porphyria
Urine that darkens on standing in the light, with abdominal pain and neurological symptoms. A specialist diagnosis.
What is usually checked next
- Urine microscopy The branch point. Red cells present means bleeding; absent with a positive strip means muscle or hemoglobin.
- A food and medication history for the past few days Settles the pigment causes without any test, and they are the commonest group.
- Creatine kinase A markedly raised value identifies muscle breakdown, which threatens the kidney.
- Kidney function and potassium if CK is raised Both can change quickly in muscle breakdown, and potassium is the one that can be immediately dangerous.
- Haptoglobin, LDH and reticulocytes if muscle is excluded Identifies red cell destruction as the source of free hemoglobin.
When to seek care sooner
- Emergency Brown or cola-colored urine after collapse, a long lie, or extreme exertion
- Emergency Passing little or no urine
- Emergency Severe muscle pain with weakness
- Same day Yellowing of the eyes with dark urine and pale stools
- Same day Flank pain with fever
- Soon Visible blood in the urine at any age
Questions worth bringing to your appointment
- Has the urine been looked at under a microscope for red cells?
- Could this be a food or a medicine I am taking?
- Should my CK be checked?
- If there are no red cells, where is the pigment coming from?
- Was the sample taken around a period?