Does refrigerating urine for 5 hours affect the Red Blood Cell (RBC) count in urine?

Does Refrigerating Urine for 5 Hours Affect RBC Count?

Yes, refrigerating urine for 5 hours can affect RBC count in urinalysis, though the specimen remains acceptable for processing if refrigerated promptly—however, you should expect potential underestimation of RBC numbers due to cell lysis and cold-induced artifacts. 1, 2

Acceptable Storage Window

• Urine specimens must be processed within 4 hours if refrigerated at 4°C to maintain diagnostic accuracy for microscopy, including RBC counts 1, 2
• At 5 hours of refrigeration, you are beyond the recommended window, which increases the risk of inaccurate RBC enumeration 1
• The gold standard remains immediate processing within 1 hour at room temperature or up to 4 hours refrigerated 1, 2

Specific Effects on RBCs After 5 Hours of Refrigeration

Cell Lysis and Degradation

• Cell lysis begins after the 4-hour refrigerated storage window, compromising microscopic findings including RBC counts 1
• RBC stability declines significantly after 24 hours of refrigeration, with approximately 25% of samples showing decreased hemoglobin reactivity (a marker of RBC breakdown) 3
• While this 24-hour data suggests some RBCs survive refrigeration, the trend toward degradation begins earlier 3

Cold-Induced Artifacts

• Refrigeration causes cold-induced precipitation and uromodulin polymer formation, which can trap cellular elements including RBCs, artificially lowering the visible count 1
• These uromodulin polymers form specifically when urine is kept cold and can obscure or aggregate RBCs during microscopic examination 1

Critical Distinction: Culture vs. Microscopy

The evidence shows different stability profiles for bacterial culture versus cellular microscopy:

• Bacterial colony counts remain stable for up to 24 hours with refrigeration 2, 4
• However, cellular elements (including RBCs) are far more labile and deteriorate within the 4-hour window 1, 2
• This distinction is crucial—guidelines permitting longer storage times refer primarily to culture specimens, not microscopic urinalysis 5

Practical Clinical Algorithm

If specimen is already at 5 hours refrigerated:

• Process the specimen but interpret RBC counts with caution—expect potential underestimation 1
• Document the 5-hour delay in your laboratory report 5
• If clinical suspicion for hematuria is high and RBC count is borderline or negative, recollect a fresh specimen 1

For future collections:

• Process within 1 hour if kept at room temperature 1, 2
• Refrigerate immediately at 4°C if processing will occur between 1-4 hours 1, 2
• Reject and recollect specimens refrigerated beyond 4 hours when accurate RBC enumeration is clinically important 1

Common Pitfalls to Avoid

• Do not assume that refrigeration "preserves" cellular elements the same way it preserves bacteria for culture—cells deteriorate even when cold 1, 3
• Never rely on specimens older than 4 hours refrigerated for definitive microscopic diagnosis of hematuria 1, 2
• Do not freeze urine intended for microscopy, as freezing completely destroys cellular elements including RBCs 1
• Specimens examined within 4 hours after voiding using conventional methods are necessary for accurate RBC morphology assessment (such as dysmorphic RBCs in glomerular disease) 6

Bottom Line for 5-Hour Refrigerated Specimens

At 5 hours of refrigeration, you are 1 hour beyond the evidence-based cutoff for reliable RBC counts. The specimen may still provide useful information, but RBC enumeration will likely be artificially low due to lysis and cold-induced trapping. For critical clinical decisions regarding hematuria, recollect a fresh specimen. 1, 2