Dipstick Hematuria

Dipstick hematuria describes the use of reagent strips to chemically detect the presence of blood within the urine. Intact urinary RBCs lyse following contact with the test paper and release hemoglobin. The peroxidase-like activity of hemoglobin oxidises a dipstick-adherent chromogen indicator, which subsequently changes color. The dipstick test can detect RBCs below 3 RBCs/hpf,12 but it has a low specificity as free hemoglobin, myoglobin, and other oxidizing agents (such as hypochloride bleaches) can give false-positive results. False-negative results can occur in the presence of reducing agents (such as vitamin C). Different commercially available dipsticks vary in their sensitivity to detect blood within urine. Most kits detect around 8 RBCs/ hpf and score the concentration as “trace,” +, ++, or +++. Recent British guidelines16 recommend that a trace of dipstick hematuria should be regarded as normal. Routine microscopy for confirmation of dipstick-positive hematuria is now generally deemed unnecessary,16 although it is often useful to perform microscopy and culture of the urine sample in order to confirm or refute the presence of infection.

Aetiology

The causes of hematuria may be classified in a number of ways, including anatomical site and pathological process (Table 26.1). Around 40% of patients with hematuria have an identifiable cause, and these are mostly bladder cancer, urinary tract infection (UTI), urinary calculus, or intrinsic renal pathology. The single commonest cause of frank hematuria in patients over the age of 50 years is bladder cancer.

Malignancy

The commonest malignancies causing hematuria are bladder and renal cancer.2 Some 85% of patients with bladder cancer have either macroscopic or microscopic hematuria.18,19 Many of the investigations outlined below are aimed at identifying these malignancies. A less common cause of hematuria is UCC arising from the upper urinary tract. Nowadays, prostate cancer rarely presents for the first time with hematuria; however, this malignancy may often be found incidentally in men undergoing hematuria investigations.

Occasionally, macroscopic hematuria may be confused with a red or brown discoloration

Urinary stones commonly cause pain associated with hematuria. Rarely, stones can cause isolated

Trauma

Trauma to the urinary tract is an important cause of hematuria. Patients with hematuria secondary to a traumatic cause usually present in an emergency setting rather than to the urology clinic. Their management and investigation is related to the traumatic incident and a detailed discussion is not included here.

Drugs

macroscopic hematuria, and staghorn calculi may present with either asymptomatic microscopic hematuria or recurrent urinary tract infections. Patients presenting with loin pain and microscopic hematuria are usually investigated in the acute setting with a noncontrast CT; however, if this fails to demonstrate a urinary calculus, then the microscopic hematuria should be investigated further as outlined below.

Infection and Inflammation

The commonest clinical scenario in which microscopic or dipstick-positive hematuria is found is with a UTI.10 As infection may be a manifestation of other uropathology, the clinician should not ignore the hematuria, and investigate the UTI as appropriate. If hematuria persists after UTI treatment then it requires investigating in its own right.

Noninfective inflammatory conditions such as radiation-induced cystitis and interstitial cystitis may cause hematuria. An associated

Numerous medications can cause hematuria.20,21 Anticoagulants such as warfarin or aspirin may cause hematuria in the presence of pathology, and therefore, these patients should still be investigated for underlying disease.11

Nephrological Causes

Renal parenchymal disease is a common cause of hematuria and includes focal glomerular diseases such as membranoproliferative glomerulonephritis, interstitial renal diseases such as drug-induced nephropathy, and systemic conditions such as systemic lupus erythematosis. Some of these conditions may cause frank hematuria. Patients with an absence of a urological cause of their hematuria require referral for a nephrological opinion if they have hypertension, significant proteinuria (defined as a total protein excretion of greater than 1,000 mg/24 h) or other indicators of renal pathology such as red cell casts of dysmorphic RBCs within a fresh urine sample.6,12 Many of these patients may require a