Evaluation of Low‑Normal Calcium with Elevated Alkaline Phosphatase and Marked Inflammatory Markers

Differential Diagnosis

The triad of low‑normal serum calcium, moderately elevated alkaline phosphatase (≈140 U/L), and markedly raised ESR/CRP most strongly points to chronic non‑bacterial osteitis (CNO), primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC), infiltrative malignancy, or sarcoidosis; therefore, immediate ordering of GGT, a comprehensive metabolic panel, PTH, 25‑hydroxy‑vitamin D, CBC with differential, and abdominal ultrasound is recommended to distinguish hepatobiliary from bone disease. 1

Metabolic bone panel – Simultaneous measurement of serum calcium, phosphate, parathyroid hormone, and 25‑hydroxy‑vitamin D is essential to rule out osteomalacia, Paget disease, hypophosphatasia, secondary hyperparathyroidism from chronic kidney disease, and vitamin D deficiency, all of which can raise alkaline phosphatase in the setting of chronic inflammation. 1
Renal function assessment – Serum creatinine with estimated glomerular filtration rate should be obtained because chronic kidney disease with secondary hyperparathyroidism is a frequent cause of isolated alkaline phosphatase elevation and may coexist with systemic inflammatory conditions. 1
FGF23 measurement – In patients with hypophosphatemia, low‑normal calcium, or clinical suspicion of X‑linked hypophosphatemia or tumor‑induced osteomalacia, intact fibroblast growth factor‑23 should be measured as a sensitive marker of phosphate‑wasting disorders. 5
Auto‑immune serology for CNO work‑up – When chronic non‑bacterial osteitis is considered, testing for anti‑cyclic citrullinated peptide antibodies, rheumatoid factor, and HLA‑B27 can help identify overlapping axial spondyloarthritis or psoriatic arthritis. 1

Whole‑body MRI – For suspected CNO, whole‑body magnetic resonance imaging (including sagittal spinal sequences) is the preferred imaging modality; technetium‑labeled bone scintigraphy or PET/CT with bone‑seeking tracers are acceptable alternatives to map clinically silent but radiologically active lesions. 1
Bone biopsy policy – Routine bone biopsy is not indicated; it should be reserved for cases where imaging is inconclusive or there is specific concern for malignancy or infectious osteomyelitis. 1

Persistent, atraumatic bone pain lasting >6 weeks, especially pain that is nocturnal or unrelated to movement, together with elevated inflammatory markers (ESR/CRP) and low‑normal calcium, is highly suggestive of CNO. 1
Diagnosis of CNO requires exclusion of other conditions; a detailed history—including personal and family history of autoinflammatory or autoimmune diseases—should be obtained. 1
Evaluation should also seek associated inflammatory manifestations such as psoriasis, inflammatory bowel disease, uveitis, or enthesitis, which may indicate a broader spondyloarthropathy spectrum. 1