Calcium - Electrolytes

Calcium

·        See also Parathyroid

Summary

·        If low Mg, then no ­ in PTH in response to ¯Ca

·        Low:

o   Hypothyroidism: abscess/gland destruction, ¯Mg, resistance to PTH (pseudo)

o   ¯Vit D: renal failure, malnutrition

·        High:

o   ­PTH: primary, secondary or tertiary

o   Paraneoplastic: PTHrH, bone metastasis

o   ­Vitamin D: nutritional, ­conversion (sarcoid)

Hypercalcaemia

·        Signs: “Bones, stones, groans and psychic moans”. Also abdominal pain, vomiting, constipation, polyuria (Ca potentiates ADH effect), depression, anorexia, weakness, ­BP, renal stones, cardiac arrest

·        Most commonly:

o   Primary hyperPTH in the community

o   Malignancy in hospital 

·        NB: acidosis ® H displaces Ca on albumin ® ­free Ca

·        If albumin raised: 

o   Urea raised ® dehydration

o   Urea normal ® cuffed specimen

·        Albumin normal or low:

o   Phosphate low or normal (and urea normal): primary or tertiary hyperparathyroidism 

o   Phosphate ­ or normal: 

§  ­ALP: Bone metastases (most common primaries are breast, kidney, lung, thyroid, prostate, ovary, colon), sarcoidosis (­Vitamin D conversion in the lungs), thyrotoxicosis 

§  Normal ALP: myeloma, vitamin D excess, Ca supplements

·        Treatment: if Ca > 3.5 mmol/l or severe symptoms:

o   Rehydrate and correct any hypokalaemia and hypomagnesaemia

o   Diuretics once rehydrated (frusemide, avoid thiazides)

o   Bisphosphonates (pamidronate): lower Ca over 2-3 days by inhibiting osteoclasts

Hypocalcaemia

·        Normal value of Ca: 2.12 – 2.65 mmol/L

·        40% of calcium is bound to albumin. Adjust Ca for changes in albumin (0.025 per 1g of Albumin). Take sample uncuffed

·        Symptoms: Tetany, depression, carpo-pedal spasm (wrist flexion and fingers drawn together), neuromuscular excitability (eg tapping over parotid causes facial muscles to twitch – Chvostek‟s sign)

·        Causes of hypocalcaemia:

o   ¯Mg ® ¯PTH ® hypocalcaemia

o   Thyroid or parathyroid surgery 

o   If ­PO4 then chronic renal failure (failure of Vitamin D conversion), hypoPTH or PseudohypoPTH 

o   If PO4 normal or ¯ then osteomalacia (­ALP), over hydration or pancreatitis