The presence of free hemoglobin (Hb) in the urine is referred to as hemoglobinuria. Hemoglobinuria can be related to conditions outside the urinary tract and occurs when there is such extensive or rapid destruction (intravascular hemolysis) of circulating erythrocytes that the reticuloendothelial system cannot metabolize or store the excess free Hb. The Hb is then filtered through the glomerulus. Hemoglobinuria may also occur as a result of lysis of RBCs in the urinary tract.

When intact RBCs are present in the urine, the term hematuria is used. Hematuria is most closely related to disorders of the genitourinary system in which bleeding is the result of trauma or damage to these organs or systems.

This test detects RBCs, Hb, and myoglobin in urine. Blood in urine is always an indicator of damage to the kidney or urinary tract.

The use of both a urine dipstick measurement and microscopic examination of urine provides a complete clinical evaluation of hemoglobinuria and hematuria. Some forms of dipsticks contain a lysing reagent that reacts with occult blood and detects intact as well as lysed RBCs.

When urine sediment is positive for occult blood but no RBCs are seen microscopically, myoglobinuria can be suspected. Myoglobinuria is caused by excretion of myoglobin, a muscle protein, into the urine as a result of (1) traumatic muscle injury, which may occur in automobile accidents, football injuries, or electric shock; (2) a muscle disorder, such as an arterial occlusion to a muscle or muscular dystrophy; (3) certain kinds of poisoning, such as carbon monoxide or fish poisoning; or (4) malignant hyperthermia related to administration of certain anesthetic agents. Myoglobin can be distinguished from free Hb in the urine by chemical tests.

Negative (<0.03 mg free Hb/dL or <10 Ercs/μL)

Ercs = erythrocytes

1. Collect a fresh random urine specimen.

   1. Hemoglobinuria (Hb in urine)

      1. Dip reagent stick into the urine; the color change on the dipstick correlates with a standardized color chart specifically used with that particular type of dipstick.

      2. The color chart indicates color gradients for negative, moderate, and large amounts of Hb.

   2. Hematuria (RBCs in urine)

      1. This dipstick method allows detection of intact RBCs when the number is >10 cells/mL of urine. The color change appears stippled on the dipstick.

      2. The degree of hematuria can be estimated by the intensity of the speckled pattern.

2. Centrifuge the urine sample and examine the sediment microscopically (see Microscopic Examination of Urine Sediment) to verify the presence of RBCs.

   1. Hemoglobinuria is suspected when no RBCs are seen or the number seen does not correspond to the degree of color on the dipstick.

   2. Myoglobinemia may be suspected if the urine is cherry-red, no RBCs are seen, and blood serum enzymes for muscle destruction are elevated.

1. Hematuria is found in:

   1. Acute UTI (cystitis)

   2. Lupus nephritis

   3. Urinary tract or kidney tumors

   4. Urinary calculi (intermittent hematuria)

   5. Malignant hypertension

   6. Glomerulonephritis (acute or chronic)

   7. Pyelonephritis

   8. Trauma to kidneys

   9. Polycystic kidney disease

   10. Leukemia

   11. Thrombocytopenia

   12. Strenuous exercise

   13. Benign familial or recurrent hematuria (asymptomatic hematuria without proteinuria; other clinical and laboratory data are normal)

   14. Heavy smokers

2. Hemoglobinuria is found in:

   1. Extensive burns

   2. Transfusion reactions (incompatible blood products)

   3. Febrile intoxication

   4. Certain chemical agents and alkaloids (poisonous mushrooms, snake venom)

   5. Malaria

   6. Bleeding resulting from operative procedures on the prostate (can be difficult to control, especially in the presence of malignancies)

   7. Hemolytic disorders such as sickle cell anemia, thalassemia, and glucose-6-phosphate dehydrogenase deficiency

   8. Paroxysmal hemoglobinuria (large quantities of hemoglobin appear in urine at irregular intervals)

   9. Kidney infarction

   10. Hemolysis occurring while the urine is in the urinary tract (RBC lysis from hypotonic urine or alkaline urine)

   11. Fava bean (broad bean) sensitivity (causes severe hemolytic anemia)

   12. Disseminated intravascular coagulation (DIC)

   13. Strenuous exercise

Pretest Patient Care

1. Explain purpose of test, procedure for urine collection, and interfering factors.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Drugs causing a positive result for blood or hemoglobin include:

   1. Drugs toxic to the kidneys (e.g., bacitracin, amphotericin)

   2. Drugs that alter blood clotting (warfarin )

   3. Drugs that cause hemolysis of RBCs (aspirin)

   4. Drugs that may give a false-positive result (e.g., bromides, copper, iodides, oxidizing agents)

2. High doses of ascorbic acid or vitamin C may cause a false-negative result.

3. High SG or elevated protein reduces sensitivity.

4. Myoglobin produces a false-positive result.

5. Hypochlorites or bleach used to clean urine containers causes false-positive results.

6. Menstrual blood may contaminate the specimen and alter results.

7. Prostatic infections may cause false-positive results.

8. see Appendix E for a complete list of drugs that affect test outcomes.