Specimen Rejection Criteria

The integrity of diagnostic testing relies heavily on the quality of the specimens received in the clinical laboratory. A specimen is accepted for processing only when it meets specific standards ensuring that the test results will be accurate, reliable, and clinically relevant. When a specimen fails to meet these standards, it must be rejected. Specimen rejection is a quality control mechanism designed to prevent the reporting of erroneous data that could lead to misdiagnosis or inappropriate patient treatment.

1. Identification and Labeling Errors

Accurate patient identification is the foundation of laboratory safety. If the specimen cannot be definitively linked to the correct patient, the potential for harm is significant. Therefore, strict criteria are applied to labels and requisition forms.

• Unlabeled Specimens: Any container received without a label must be rejected immediately. There is no acceptable workaround for a completely unlabeled specimen.
• Mismatched Information: If the information on the specimen label does not match the information on the test requisition, the specimen is rejected. This includes discrepancies in patient name, date of birth, or hospital ID number.
• Illegible Labels: Labels that are handwritten, torn, stained with blood, or otherwise rendered unreadable are grounds for rejection. Barcodes must be scannable and intact.
• Missing Time or Date: For certain time-sensitive tests (such as therapeutic drug monitoring or glucose levels), the absence of collection time and date makes the result impossible to interpret, necessitating rejection.

2. Hemolysis

Hemolysis is the breakdown of red blood cells, releasing hemoglobin into the serum or plasma. This is one of the most common reasons for specimen rejection in clinical chemistry. Hemolysis can occur due to rough handling of the tube, using a needle that is too small, or forcefully drawing blood into a syringe.

• Visual Detection: Serum or plasma that appears pink or red (rather than straw-colored) indicates hemolysis.
• Interference: Hemolyzed specimens are rejected because hemoglobin interferes with the photometric methods used in chemistry analyzers. It can falsely elevate potassium, lactate dehydrogenase (LD), and AST, while falsely lowering sodium and bicarbonate levels.
• Severity Criteria: Mild hemolysis may be accepted with a disclaimer, but moderate to severe hemolysis almost always requires a recollection.

3. Clotted Samples

Anticoagulants are added to blood collection tubes to prevent clotting. If a clot forms in an anticoagulated tube (such as a lavender-top EDTA tube), the specimen is unsuitable for testing.

• Hematology: Clots will clog the automated cell counters, leading to inaccurate complete blood counts (CBC) and potentially damaging the instrument.
• Coagulation Studies: In citrate tubes (light blue top), even a tiny fibrin strand can invalidate clotting time tests like PT and INR, as it consumes the clotting factors being measured.
• Cause: Clotting usually occurs because the tube was not mixed gently by inversion immediately after collection, or it sat for too long before processing.

4. Incorrect Anticoagulant or Additive

Different laboratory tests require specific chemical environments. Using the wrong tube type compromises the analytes being measured.

• Electrolytes: Using EDTA (lavender top) instead of a serum separator or heparin tube will falsely lower potassium and calcium levels because EDTA chelates (binds) these metals.
• Glucose: Fluoride oxalate (gray top) tubes contain a glycolysis inhibitor to preserve glucose. If blood for glucose is collected in a plain tube without preservative and not processed quickly, glucose levels will drop significantly due to consumption by blood cells.
• Contamination: Carryover of additives from one tube to another during the draw order (draw order error) can also lead to rejection due to cross-contamination.

5. Insufficient Volume

The ratio of blood to the anticoagulant or preservative in the tube is critical. "QNS" (Quantity Not Sufficient) is a common rejection code.

• Ratio Dilution: If a tube is underfilled, the liquid anticoagulant makes up a higher percentage of the total volume. This effectively dilutes the blood sample, leading to falsely low analyte concentrations.
• Coagulation Sensitivity: The light blue top tube for coagulation is extremely sensitive to fill volume. It must be filled to the exact mark indicated on the tube (usually to 90% or 100% capacity) to maintain the correct 9:1 blood-to-anticoagulant ratio. Any deviation mandates rejection.
• Running Tests: There simply may not be enough specimen physically available to run the panel of tests ordered by the physician.

6. Container Integrity and Transport Issues

The physical condition of the specimen and the conditions of transport are vital for maintaining sample stability.

• Leaking or Broken Containers: A specimen that is leaking poses a biohazard risk and may be contaminated by external fluids. These cannot be accepted.
• Wrong Container: Urine collected in a non-sterile cup for culture, or a stool specimen submitted in a container without preservative, will be rejected.
• Temperature Excursions: Certain specimens must be kept frozen, refrigerated, or kept at room temperature.
  • Ammonia and arterial blood gases must be transported on ice and analyzed immediately.
  • Cryoglobulins must be kept warm (37C) during transport.
  • Specimens for serum separator tubes generally need to clot at room temperature before centrifugation.
• Delays in Transport: Prolonged transit time can lead to cellular degradation, bacterial overgrowth in cultures, or changes in pH. Most specimens have a defined "stability window" (e.g., must be received within 2 hours of collection).

7. Inappropriate Specimen Type

Sometimes the specimen collected is of the wrong biological matrix for the test ordered.

• Attempting to run a test that requires serum (e.g., many cardiac enzymes) on whole blood or plasma.
• Submitting a throat swab for a test that requires a nasopharyngeal swab.
• Sending clotted blood for a blood culture (which requires sterility and living organisms to grow).

Consequences and Process

When a specimen is rejected, the laboratory must immediately notify the nursing unit or the phlebotomy team. The goal is to obtain a new specimen as quickly as possible to avoid delays in patient care.

Adherence to strict specimen rejection criteria is not about bureaucracy; it is a core component of patient safety. By refusing to analyze compromised samples, the laboratory protects patients from the risks of misdiagnosis and ensures the medical data provided to clinicians is of the highest possible quality.