Does ACCR Require 24-Hour Urine Collection?
No, the amylase/creatinine clearance ratio (ACCR) does not require a 24-hour urine collection—it can be calculated from a spot (untimed) urine sample along with simultaneous serum measurements of amylase and creatinine. 1, 2
How ACCR is Calculated
The ACCR is calculated using the following formula:
ACCR = (Urine amylase × Serum creatinine) / (Serum amylase × Urine creatinine) × 100
This calculation requires:
- A single spot urine sample for urine amylase and urine creatinine 1
- A simultaneous blood sample for serum amylase and serum creatinine 2
- No timed collection is necessary 1
Alternative Simplified Approach
The urine amylase-to-urine creatinine ratio (uAm/uCr) from a spot urine sample alone correlates even better with serum amylase than ACCR does (r = 0.779 vs r = 0.374), making it a superior alternative that eliminates the need for blood sampling entirely. 1 This ratio had significantly higher diagnostic accuracy (AUC 0.884) compared to ACCR (AUC 0.666) for predicting hyperamylasemia, with a cutoff value of 569.8 providing 81% sensitivity and 83% specificity. 1
Important Clinical Caveats
Specificity Limitations
- ACCR is not specific for acute pancreatitis—it reflects defective proximal tubular reabsorption of amylase, which occurs in virtually all patients with acute pancreatitis but also in other conditions. 2
- Burns, diabetic acidosis, and other conditions causing acute tubular dysfunction can elevate ACCR without pancreatitis. 2
- In chronic renal insufficiency, ACCR values are significantly elevated (mean 3.5 vs 2.64 in controls) even without pancreatic disease, making interpretation unreliable in this population. 3
Assay Method Considerations
- The amylase assay technique significantly affects ACCR values: saccharogenic methods yield ACCR of ~2.2%, iodometric ~1.5%, and chromogenic ~0.8%. 4
- Each method requires its own reference range for accurate interpretation. 4
- Recovery of amylase from urine is less than 50% with iodometric and chromogenic techniques unless albumin is added to the urine assay system. 4
Diagnostic Performance
- ACCR has lower sensitivity (73%) and specificity (75%) compared to serum amylase (98% sensitivity) or the urine amylase/creatinine ratio (98% sensitivity) for diagnosing acute pancreatitis. 5
- ACCR changes are delayed relative to increases in serum amylase and urine amylase. 5
- ACCR specificity is particularly poor in patients with acute surgical abdomen and concurrent renal dysfunction, as creatinine clearance falls more rapidly than amylase clearance. 5
Practical Recommendation
For clinical management of suspected hyperamylasemia or pancreatitis, use serum amylase or the spot urine amylase/creatinine ratio rather than ACCR, as these provide superior diagnostic accuracy without the complexity and limitations of clearance calculations. 1, 5 If ACCR must be used, ensure you know your laboratory's amylase assay method and corresponding reference range, and interpret cautiously in patients with renal impairment. 3, 4