Urine Blood

Your kidneys filter your blood and send the waste out as urine. A healthy urinary tract holds red blood cells back, so normal urine carries essentially none.

The dipstick pad reacts to heme, the iron-rich core of a red blood cell, and turns green or blue when it finds it. That same reaction also lights up for free hemoglobin or muscle myoglobin, two other heme-carrying proteins, so a positive strip gets confirmed by counting actual cells under a microscope.

A positive reading tells you to repeat the test and look a little closer. Most of the time the cause is everyday and benign: a hard workout, your period, dehydration, or a passing infection. Because the urinary tract runs a long way, hidden blood can also be an early clue to a stone, an infection, inflammation in the kidney's filters, or, less often, a tumor. Blood you can see carries more weight than the microscopic kind.

There's no "too little" here. Negative is the goal, and a positive strip is one signal, not an answer. The standard confirms true microscopic blood at 3 or more red blood cells per high-power field under the microscope, so read this alongside that follow-up and your clinician. Caught at the dipstick stage, the common causes are usually straightforward to sort out and treat.