Ceftriaxone is a third-generation cephalosporin antibiotic frequently prescribed to treat a wide range of bacterial infections. While generally safe, clinicians and lab professionals must be aware of its potential to alter laboratory test results. These effects can be due to direct physiological changes or, in some cases, drug interference that causes misleading readings. This article explores the specific laboratory tests that can be affected by ceftriaxone therapy.
Hematologic Effects on Blood Labs
Ceftriaxone is known to cause a variety of hematologic abnormalities, which are among the most common adverse effects observed during therapy.
- Complete Blood Count (CBC): Alterations in the CBC are possible. This can include an increase in eosinophils (eosinophilia) and platelets (thrombocytosis), or a decrease in white blood cells (leukopenia, neutropenia). In rare, but serious, cases, it can cause drug-induced immune hemolytic anemia (DIIHA), which results in a sharp and dangerous drop in hemoglobin.
- Erythrocyte Agglutination: Ceftriaxone can cause red blood cells to clump together (agglutinate). This can lead to erroneous results on automated hematology analyzers, producing incorrectly high values for mean corpuscular hemoglobin concentration (MCHC) and inaccurate counts for red blood cell (RBC) parameters. A peripheral blood smear is often needed to confirm the agglutination.
- Markers of Hemolysis: In cases of DIIHA, additional lab findings can include low haptoglobin, elevated lactate dehydrogenase (LDH), and hyperbilirubinemia, all of which are indicators of red blood cell destruction.
Hepatic and Renal Function
Monitoring of liver and kidney function is routine during ceftriaxone therapy, as abnormalities can occur.
- Elevated Liver Enzymes: Ceftriaxone can cause transient elevations of liver enzymes such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Elevations in alkaline phosphatase (ALP) and bilirubin have also been reported.
- Biliary Sludge: The drug is excreted in the bile and can form precipitates with calcium, leading to biliary pseudolithiasis (sludge). While often asymptomatic, this can affect liver function and is a notable adverse event, particularly in children.
- Renal Function Markers: Elevations in blood urea nitrogen (BUN) and serum creatinine, though less common, can indicate an effect on kidney function. Urine analysis may also show casts.
Coagulation Profiles
For patients on ceftriaxone, especially those on anticoagulants, careful monitoring of coagulation is necessary.
- Prolonged Prothrombin Time (PT): Ceftriaxone has been associated with prolongation of the prothrombin time, which measures how long it takes for blood to clot. This risk is heightened when the drug is co-administered with anticoagulants like heparin or warfarin.
- Reversible with Vitamin K: The effect on PT is typically reversible with vitamin K administration, which suggests the interference is related to vitamin K metabolism.
False-Positive and False-Negative Lab Results
Several diagnostic tests can produce inaccurate results due to interference from ceftriaxone, not because of a true underlying medical condition.
- False-Positive Coombs Test: A direct Coombs test may become positive during ceftriaxone therapy. This indicates the presence of antibodies on red blood cells, but it is not always associated with active hemolysis and can be misleading.
- False-Positive Urinary Glucose: Non-enzymatic methods for measuring urine glucose (e.g., Clinitest) can give false-positive results in patients receiving ceftriaxone. To avoid this, enzymatic methods (like TesTape) should be used.
- False-Negative Blood Glucose Readings: Conversely, ceftriaxone can interfere with some home blood glucose monitoring systems, leading to falsely low readings. This is a critical point for diabetic patients who must use an alternative testing method if necessary.
- False-Positive Galactosemia Test: Ceftriaxone may also cause a false-positive result in tests for galactosemia.
Critical Considerations in Neonates: Bilirubin Displacement
Ceftriaxone is specifically contraindicated in hyperbilirubinemic neonates, particularly premature infants. The drug can displace bilirubin from its binding sites on serum albumin. This increases the concentration of free bilirubin in the bloodstream, raising the risk of kernicterus or bilirubin encephalopathy. Additionally, the co-administration of ceftriaxone with intravenous calcium-containing solutions is contraindicated in neonates due to the risk of ceftriaxone-calcium precipitation.
Summary of Lab Impacts: Comparison Table
| Lab Category | Affected Tests | Specific Effect | Notes |
|---|---|---|---|
| Hematology | CBC (RBC, Hgb, WBC, Platelets), LDH, Coombs Test | Eosinophilia, thrombocytosis, leukopenia, anemia (including DIIHA), high LDH, positive Coombs | Hemolytic anemia is a rare but serious side effect. Erythrocyte agglutination can interfere with automated counts. |
| Hepatic Function | ALT, AST, ALP, Bilirubin | Elevations in liver enzymes and bilirubin. Biliary sludge formation. | Effects can be transient and often resolve after discontinuation. |
| Renal Function | BUN, Creatinine, Urine Analysis | Increased BUN and creatinine; presence of casts in urine. | Changes are typically minor but indicate monitoring is prudent. |
| Coagulation | Prothrombin Time (PT) | Prolonged clotting time. | Important for patients on anticoagulants; reversible with Vitamin K. |
| Glucose Testing | Urine Glucose, Blood Glucose | False-positive urine glucose (non-enzymatic), false-low blood glucose (some home monitors). | Use enzymatic urine tests; verify glucose monitor compatibility. |
| Neonates | Bilirubin, Calcium | Displaces bilirubin from albumin. Potential precipitation with IV calcium. | Contraindicated in hyperbilirubinemic neonates and with IV calcium. |
Conclusion
While ceftriaxone is an effective antibiotic, its potential for influencing laboratory test results is significant and multifaceted. From causing false-positive diagnostic tests like the Coombs and urine glucose to inducing genuine physiological changes in hematology, coagulation, and organ function, a careful approach is warranted. Clinicians should maintain a high index of suspicion for drug-induced lab abnormalities, particularly when unexpected results arise. For patients, particularly those with diabetes or specific risk factors like hyperbilirubinemia in neonates, knowing these interactions is crucial for ensuring accurate diagnosis and patient safety. Communicating all medications to lab personnel is a simple but vital step to prevent misinterpretation of results during therapy.
