I HAVE A PATIENT WITH HEMATURIA
How do I determine the cause?
Constructing and Ranking a DDx
CONSTRUCTING A DIFFERENTIAL DIAGNOSIS
Diagnostic approach to nonvisible (microscopic) hematuria.
Red urine is not always caused by hematuria. A variety of medications, food dyes, and metabolites can cause heme-negative red urine, or pigmenturia (Table 21-1). Furthermore, not all dipstick tests positive for blood are due to hematuria. In addition to detecting heme in intact red blood cells (RBCs), urine dipsticks detect free hemoglobin (commonly associated with hemolytic anemia) and myoglobin (commonly associated with rhabdomyolysis), hence leading to false-positive tests for hematuria.
Table 21-1.Causes of heme-negative red urine (pigmenturia). |Favorite Table|Download (.pdf) Table 21-1. Causes of heme-negative red urine (pigmenturia).
|Causes ||Examples |
|Medications || |
|Food dyes || |
|Metabolites || |
Whenever the urine dipstick is positive for blood, and the microscopic exam of the urine does not show RBCs, myoglobinuria and hemoglobinuria should be considered.
True gross (visible) hematuria is always pathologic. Microscopic (nonvisible) hematuria may be transient, spurious, or persistent. Transient causes of microscopic hematuria include urinary tract infections (UTIs) (which sometimes also cause gross hematuria) and strenuous exercise; hematuria due to these causes would be expected to resolve on repeat testing after 48 hours of treatment or after discontinuing exercise for 72 hours. Spurious causes include urinary contamination from menstruation and sexual intercourse in women. This chapter will focus on persistent, true hematuria.
All patients with hematuria should have a urine culture performed, regardless of the likelihood of infection.
The differential diagnosis of hematuria is often divided into microscopic hematuria or gross hematuria. Microscopic hematuria is present when microscopic inspection of at least 2 properly collected urine specimens show > 3 RBCs per high-powered field (hpf). Gross hematuria is red or brown urine, sometimes with blood clots. However, there is considerable overlap in the causes of microscopic and gross hematuria, and it may be more practical to first consider whether the hematuria is glomerular in origin. Pivotal points that help distinguish glomerular hematuria from nonglomerular hematuria include dysmorphic RBCs (acanthocytes), red cell casts, new or acutely worsening hypertension or proteinuria, and increased creatinine. While these abnormalities may also be seen in some of the interstitial and vascular causes of hematuria, they will not be found when hematuria is caused by a renal structural abnormality or an abnormality distal to the kidneys. Visible blood clots, which are never due to a glomerular cause, are another pivotal point, indicating a lower urinary tract source of the hematuria.