Laboratory Blood Tests for Suspected Lower Extremity Bone Cancer
For a patient with suspected lower extremity bone cancer, obtain alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) levels, along with a complete blood count (CBC) with differential, comprehensive metabolic panel including electrolytes (magnesium and phosphate), renal and liver function tests, coagulation profile, and blood group typing. 1
Prognostic Markers
While there are no specific diagnostic laboratory tests for bone cancer, two serum markers have established prognostic value:
- Alkaline Phosphatase (ALP): Elevated levels correlate with adverse outcomes in osteosarcoma and should be measured at baseline 1
- Lactate Dehydrogenase (LDH): Elevated levels also correlate with adverse outcomes and predict higher risk of metastatic disease 1, 2
The NCCN guidelines specifically recommend that CBC, LDH, and ALP should be performed before initiation of treatment for suspected bone cancer 1. These markers are particularly important as elevated serum ALP or LDH are recognized adverse prognostic factors, especially when combined with proximal extremity tumor location, large tumor volume, or detectable metastases 1.
Comprehensive Baseline Laboratory Panel
Essential Tests for Treatment Planning
The following laboratory tests are required before starting interdisciplinary treatment, as chemotherapy for bone cancer can cause significant organ toxicity 1:
- Complete blood count with differential: Assesses baseline hematologic status 1
- Blood group typing: Required for potential transfusions during surgery 1
- Coagulation profile: Evaluates bleeding risk before biopsy and surgery 1
- Serum electrolytes including magnesium and phosphate: Baseline assessment for chemotherapy monitoring 1
- Renal function tests: Critical as chemotherapy can cause renal dysfunction 1
- Liver function tests: Baseline hepatic assessment 1
- Hepatitis and HIV testing: Required before chemotherapy initiation 1
Clinical Context and Interpretation
Understanding ALP and LDH Significance
When ALP is elevated with normal GGT, this strongly suggests bone origin rather than hepatic pathology 3. In the context of suspected bone cancer in an elderly patient or someone with previous fracture, elevated ALP warrants careful evaluation to distinguish between benign bone turnover (fracture healing, Paget's disease) and malignant processes (bone metastases, primary bone cancer) 3, 4.
Research demonstrates that LDH >850 IU/L and ALP >280 IU/L are predictive of skeletal metastases in osteosarcoma patients 5. The percentage of patients with elevated serum LDH at diagnosis is significantly higher in those with metastatic disease (64%) versus localized disease (33%) 6.
Prognostic Value
Both markers have established prognostic significance:
- Elevated LDH correlates with higher disease burden and poorer outcomes in bone sarcomas 2
- Elevated ALP is associated with adverse outcomes in osteosarcoma 2, 3
- These markers are incorporated into risk stratification systems 2
Important Caveats
Do not rely on laboratory tests alone for diagnosis. Plain radiography remains the preferred initial diagnostic test, and tissue biopsy is required for definitive diagnosis 7. The primary symptom of bone cancer is pain occurring at rest or at night, often accompanied by swelling or decreased joint range of motion 8.
Timing matters. All staging investigations, including laboratory tests, should be completed before biopsy to avoid contamination of tissue planes and ensure accurate baseline assessment 1.
Refer promptly. Any patient with radiographic suspicion of bone malignancy should be quickly referred to a cancer center or bone sarcoma reference center for multidisciplinary evaluation before further workup 1, 7.