Chondrocalcinosis (calcium pyrophosphate crystal disease): look for a metabolic cause

Fasting laboratory tests

• Serum calcium
• Serum albumin
• Serum phosphate
• Serum ferritin
• Transferrin saturation (in the morning, fasting)
• Serum magnesium (onset before 55-60, diffuse or polyarticular form, or known cause of hypomagnesaemia)if needednon-French guidelineHypomagnesaemia is a recognised metabolic cause ^[2,3]; the search for metabolic causes is particularly needed before age 55 or in diffuse polyarticular chondrocalcinosis ^[4].
• PTH, on the same sample as the serum calcium (if serum calcium raised or high-normal)if neededSerum calcium screens for primary hyperparathyroidism, completed if needed by PTH ^[1]; after age 55, hyperparathyroidism should be considered in all patients ^[4].
• Alkaline phosphatase (ALP) (if onset before 60)if needednon-French guidelineA leading American review (N Engl J Med, 2016) recommends, before age 60, looking for all associated metabolic diseases, including hypophosphatasia, due to a functional deficiency of alkaline phosphatase, by measuring alkaline phosphatase among others ^[5]. The COFER (French College of Rheumatology) says to look routinely for the two main causes, haemochromatosis and primary hyperparathyroidism ^[1]. Low alkaline phosphatase suggests hypophosphatasia ^[5].