A 36 year old male presents with a complaint of passing dark-reddish urine. He states that yesterday he played basketball for 4 hours, which was the first time he had exercised in 4 months. He awoke this morning with sore muscles and discolored urine. Physical examination is unremarkable. The urine is reddish-brown in color; dipstick test for blood is positive, the pH is 5.1, the specific gravity 1.03. Microscopic examination of the urine reveals no red blood cells. What is the most likely etiology for this presentation?
The appearance of a dark-reddish urine is suggestive of a number of conditions, including hematuria; however, there are no red blood cells present on microscopic examination. Fuhermore, the dipstick test for blood is positive, which is suggestive of myoglobinuria. Myoglobin is a pigment that, if present in the urine, will produce a positive dipstick test, even in the absence of red blood cells. Myoglobinuria can be caused when an unconditioned individual paakes in intense physical exeion. This extreme physical activity leads to muscle cell breakdown and the release of myoglobin into the blood, which is then filtered by the kidneys and excreted into the urine. If there was hemolyzed blood in the urine , a few red blood cells should have been detected on urinalysis. Ingestion of foods that contained red dye can discolor the urine; however, it would not produce a positive dipstick test. Nephrolithiasis generally results in the appearance of blood cells in the urine. Ref: Kennelly P.J., Rodwell V.W. (2011). Chapter 6. Proteins: Myoglobin & Hemoglobin. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.
Hemolyzed blood in the urine
Ingestion of foods that contained red dye C. Myoglobinuria
Myoglobinuria
Nephrolithiasis