What does ASC (Ascaris) levels in urinalysis indicate?

ASC in Urinalysis: Ascorbic Acid (Vitamin C), Not Ascaris

ASC on a urinalysis report refers to ascorbic acid (vitamin C) levels in the urine, not Ascaris parasites. This is a critical distinction that prevents unnecessary parasitic workup and focuses attention on the clinically relevant issue of test interference.

What ASC Actually Measures

• ASC indicates the concentration of ascorbic acid (vitamin C) present in the urine specimen 1
• Ascorbic acid is routinely measured on modern urine dipstick panels because it can cause false-negative results in multiple urine tests 1
• The measurement serves as a quality control indicator to alert clinicians when other test results may be unreliable 1

Clinical Significance: Test Interference

• High urinary ascorbic acid concentrations (>400 mg/L) can cause false-negative results for glucose and hemoglobin/blood on urine dipsticks 1
• Even clinically relevant low concentrations of erythrocytes (10/μL), hemoglobin (0.03 mg/dL), and glucose (50 mg/dL) may be missed when ascorbic acid levels are elevated 1
• This interference creates a risk of overlooking important clinical findings, particularly in diabetic patients (missed glucosuria) or those with hematuria 1

When to Suspect Interference

• If ASC is elevated (typically >50-100 mg/dL) AND glucose or blood tests are negative, consider repeating the urinalysis after the patient discontinues vitamin C supplements for 24-48 hours 1
• Patients taking high-dose vitamin C supplements (>500 mg daily) are at highest risk for interference 1
• Consider manual microscopy for red blood cells if hematuria is clinically suspected but dipstick is negative with elevated ASC 1, 2

Common Pitfall to Avoid

• Do not confuse ASC with Ascaris lumbricoides infection 3, 4
• Ascaris is an intestinal helminth diagnosed by microscopic examination of stool for characteristic ova, not by urinalysis 3
• Ascaris does not appear in urine under normal circumstances and would not be detected by standard urinalysis 3

Practical Management Algorithm

1. Check the ASC level on every urinalysis report 1
2. If ASC is elevated (>50 mg/dL):
   • Question the patient about vitamin C supplement use 1
   • Interpret negative glucose and blood results with caution 1
   • Consider repeat testing after supplement discontinuation if clinical suspicion remains high 1
3. If ASC is normal (<50 mg/dL):
   • Proceed with standard interpretation of all urinalysis parameters 1, 5, 2