- Elevated corrected Ca2+.
- Low PO43-.
- Normal alkaline phosphatase.
- Normal or elevated serum PTH.
- High 24 hr urinary Ca2+.
- To exclude Familial Hypocalcuirc Hypercalcaemia (FHH), the calcium clearance to creatinine clearance ratio should be > 0.01. This is calculated as follows:
[Urine Calcium (mmol/l) x urine volume (ml)] / [ Plasma Calcium (mmol/l) x 1440]
Creatinine Clearance (This may be calculated already)
[Urine Creatinine (mmol/l) x urine volume (ml)] / [ Plasma Creatinine (mmol/l) x 1440]
Plasma creatinine is normally expressed in umol/l and needs to be converted to mmol/l by dividing by 1000.
However, this ratio can be reduced to
Urine Calcium (mmol/l) x [Plasma Creatinine (umol/l) / 1000]
Plasma Calcium (mmol) x Urine Creatinine (mmol/l)
Urine calcium 1.0 mmol/l Ratio = 1.0 x [130/1000] = 0.0079
Urine creatinine 6.2 mmol/l 2.65 x 6.2
Plasma creatinine 130 umol/l
Plasma calcium 2.65 mmol/l
Urine calcium 2.2mmol/l Ratio = 2.2 x [74/1000] = 0.035
Urine creatinine 1.4 mmol/l 3.3 x 1.4
Plasma creatinine 74 umol/l
Plasma calcium 3.3 mmol/l
LOCALISATION OF PARATHYROID ADENOMA
None of the techniques are reliable and often a combination of methods are used.
- Ultrasound of neck.
- Sesta-MIBI scanning.
- 123I and sesta-MIBI double isotope scan (higher sensitivity, ask nuclear medicine).
- MRI of neck.
- CT neck (+ upper mediastinum).
- Selective venous sampling for PTH is not routinely used and reserved for difficult cases. Patient requires hospital admission, and investigation needs to be booked with Dr Jackson well in advance.
MANAGEMENT PRIOR TO PARATHYROIDECTOMY
- Usual pre-operative bloods, including U+E, Ca2+, PO4, alkaline phosphatase, albumin.
- Maintain adequate hydration.
- Replace deficit and maintain 3-4 l fluids /day i.v. and then orally if patient able to drink.
- If above measures do not reduce corrected Ca2+ <2.8 mmol/l give bisphosphonates (e.g. pamidronate 30 mg in 1l 0.9% saline over 4 hrs). This will not start to work for 24hrs, with maximum effect 5-6 days. Plan in advance to avoid severe post-operative hypocalcaemia.
MANAGEMENT AFTER PARATHYROIDECTOMY
- Enquire for symptoms of hypocalcaemia (paraesthesiae, cramps etc.).
- Trousseau's and Chvostek's test daily.
- Daily U+E and corrected Ca2+.
- If mild symptoms and corrected Ca2+ >2.0 mmol/l, give effervescent Ca2+ (Sandocal).
- If severe symptoms and corrected Ca2+ <2.0 mmol/l, give Ca2+ infusion (calcium gluconate 15 mg/kg i.v. in 1l 0.9% saline over 4 hours).
- If hypocalcaemia persists, introduce alfacalcidol (0.125 ng od).