Can a whole‑blood specimen left at room temperature for five hours be used for laboratory tests, or should it be discarded?

Blood Specimen Viability After 5 Hours at Room Temperature

A whole blood specimen left at room temperature for 5 hours can be used for most routine laboratory tests, including complete blood counts and many metabolic panels, as this falls well within acceptable stability timeframes for the majority of common analyses.

Test-Specific Stability Guidelines

Hematologic Testing (Complete Blood Count)

• Most CBC parameters remain stable for at least 24 hours at room temperature, including WBC, RBC, hemoglobin, hematocrit, and platelet counts 1
• For K3EDTA specimens specifically, hematologic testing should ideally be performed within 6 hours, though modern hematology instruments may extend this window if validated by the laboratory 2
• At 5 hours, your specimen is acceptable for CBC analysis with reliable results 1, 3

Metabolic Panel Testing

• Comprehensive metabolic panel (CMP) testing is more time-sensitive, with reliable results typically requiring processing within 12 hours when stored at 4°C 1
• At room temperature, metabolic parameters like glucose, AST, ALT, and electrolytes show less stability compared to refrigerated storage 1
• However, at 5 hours room temperature storage, most CMP parameters remain within acceptable limits for clinical decision-making 1

Immunophenotyping and Flow Cytometry

• For specialized testing like CD4+ T-cell counts, specimens can be maintained at room temperature (18-22°C) and processed within 30-48 hours 2
• Your 5-hour specimen is well within this acceptable window for flow cytometric analysis 2

Critical Considerations Before Processing

Visual Inspection Requirements

Before accepting any specimen, you must inspect for 2:

• Hemolysis (reject if present)
• Clot formation (reject if visible clots)
• Freezing (reject if frozen)
• Temperature extremes (note on report if specimen feels hot or cold, but may still process if not hemolyzed) 2

Temperature Exposure

• Specimens should have been maintained between 18-22°C (64-72°F) during the 5-hour period 2
• Avoid exposure to temperatures >37°C (99°F) or <10°C, which can cause cellular destruction 2

Practical Algorithm for 5-Hour Room Temperature Specimens

Accept and process if:

• No visible hemolysis, clotting, or freezing 2
• Specimen maintained at appropriate room temperature 2
• Testing includes: CBC, basic metabolic panel, immunophenotyping 1, 2

Process with notation if:

• Specimen feels warm or cool but shows no hemolysis 2
• Document temperature condition on worksheet and final report 2

Reject and request new specimen if:

• Visible hemolysis, clots, or evidence of freezing 2
• Known exposure to extreme temperatures with cellular compromise 2
• Specialized coagulation studies requiring immediate processing

Important Caveats

Test-Specific Exceptions

• Blood cultures and microbiological specimens should be transported and processed as rapidly as possible, ideally within 2 hours at room temperature 2
• Platelet function testing shows progressive impairment with storage time, even at 5 hours 4
• Some coagulation factors may begin declining, though most remain within physiological range 4

Documentation Requirements

• Always document the time of collection and time of receipt in the laboratory 2
• Note any temperature concerns or delays on the laboratory worksheet 2
• This creates an audit trail for quality assurance and result interpretation 2

The 5-hour timeframe at room temperature represents a safe window for most routine laboratory testing, falling well within established stability guidelines for common hematologic and chemistry analyses 1, 2.