Urine Blood: Multistix
Hemoprotein reaction

"Blood" on the dipstick represents the reaction observed when the "peroxidase-like" activity inherent in molecules of heme (iron within a porphyrin ring) reacts with a peroxidase substrate in the pad. Note that the test is now called "Heme"which is a more accurate term for what the test is detecting, rather than the term "blood".

The table below illustrates how blood results from the dipstick (Multistix) correlates to those from the Criterion, the machine used to "read" the dipstick at Cornell University.

Multistix
(Blood)
Criterion
(Heme)*
Neg
Neg
Non-hemolyzed
Trace
Trace
Moderate
1+
Hemolyzed
Trace
Trace
Small (1+)
1+
Moderate (2+)
2-3+
Large (3+)
4+


* Heme results from the Criterion indicate the following:

  • Trace: Equivalent to hemoglobin in 10 rbcs/μL
  • 1+: Equivalent to hemoglobin in 25 rbcs/μL
  • 2+: Equivalent to hemoglobin in 50 rbcs/μL
  • 3+: Equivalent to hemoglobin in 150 rbcs/μL
  • 4+: Equivalent to hemoglobin in ≥250 rbcs/μL

Heme is found within hemoglobin (free in the urine or within erythrocytes) or myoglobin. Thus, the reaction is very sensitive and will detect hematuria, hemoglobinuria and myoglobinuria as indicated in the table below.

 
Hematuria Hemoglobinuria Myoglobinuria
Mechanism - RBCs lyse on contact with the reagent pad, causing a positive reaction (speckled pattern may result if low-grade)
Mechanism - free Hb filtered into urine as a result of hemoglobinemia (usually detectable as a visibly red plasma).
Mechanism - free Mb filtered into urine as a result of myoglobinemia (not visually detectable in plasma).
Clinical - Bleeding into urinary space (can occur at any level of the urinary or reproductive tract). Commonly due to inflammation, trauma, neoplasia, hemostatic disorders.
Clinical - Intravascular hemolysis of any cause (immune-mediated, toxic, mechanical, infectious, etc).
Clinical - Myocyte injury allowing release of myoglobin which reaches bloodstream and is readily filtered at the glomeruli.
 
Differentiation of hemoglobinuria vs. myoglobinuria by direct testing of urine alone is generally impractical. Interpretation of a positive hemoprotein result in light of the case context and the results of urine sediment, clinical chemistry and hematology examinations usually allows indirect identification as follows:
  • Hematuria: RBC will be present on urine sediment examination (if hematuria is marked, a red precipitate forms after centrifugation of urine). Note that RBCs can lyse in very alkaline or dilute urine or in urine that is stored for some time, so intact RBCs may not be seen in these settings even though there was hematuria.
  • Hemoglobinuria: There will be no RBC on the urine sediment and the urine supernatant will be red (remember that RBC will lyse in very dilute, alkaline or "old" urine). In general, affected animals have a low hematocrit (in rare cases of intravascular hemolysis, the hematocrit may be normal due to concurrent dehydration or splenic contraction).
  • Myoglobinuria: There will be no RBCs on the urine sediment and the urine will have a red supernatant (if there is a lot of myoglobin in the urine). The affected animal will have a very high CK and (usually) high AST, reflecting muscle injury.
  • In rare instances, myoglobinuria and hemoglobinuria can pre-exist in a single patient, e.g. a horse with red maple leaf poisoning (an oxidant-induced hemolytic anemia) with concurrent rhabdomyolysis. The distinction between hemoglobin and myoglobin as the cause for the red urine color is academic at this point.

 

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