Urinalysis - The Carter Center

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4.7 Determination of Hemoglobin
Introduction
Hemoglobin is a respiratory pigment in red blood cells composed of an
iron- containing group (heme) and a complex protein (globin). In
combination as hemoglobin it has the property of forming a reversible
combination with oxygen. So, it serves as a transporter of oxygen in the
blood from the lung to metabolically active tissues. It also transports
carbon dioxide and hydrogen ions to the lung from metabolically active
tissues.
Hemoglobin appears in the urine when there is extensive or rapid
destruction
(hemolysis) of circulating erythrocytes that the reticuloendothelial
system cannot metabolize or store the excessive amounts of free
hemoglobin.
Normal Value: The renal threshold for hemoglobin is 1.0 - 1.4 g/1.
Clinical significance
The presence of free Hemoglobin in the urine is referred to as
hemoglobinuria. Hemoglobinuria is usually related to hematuria- a
condition when intact red blood cells are present in the urine. Hematuria
is used to indicate bleeding somewhere in the urinary tract.Usually both
red blood cells and hemoglobin mark this disorder. Therefore, hematuria
can be distinguished from hemoglobinuria by a microscopic examination
of the sediment from a fresh urine specimen.The presence of
hemoglobin and the absence of red cells in the urine does not
necessarily mean that the hemoglobin was originally free urinary
hemoglobin. Red cells rapidly lysis in urine, especially when it has a
specific gravity of 1.006 or less or is alkaline. For this reason urine
should be absolutely fresh when examined for the presence of red cells.