Why hyperparathyroidism causes kidney stones and what the nurse does

Follow parathyroid hormone to high blood calcium

Parathyroid hormone normally keeps blood calcium in a narrow range. It releases calcium and phosphate from bone, increases calcium reabsorption in the kidney, and stimulates activation of vitamin D, which raises calcium absorption from the gut. In primary hyperparathyroidism, one or more glands secrete too much hormone regardless of the calcium level.

The combined effect is hypercalcaemia. Although the hormone increases calcium reabsorption in each nephron, the much larger amount of calcium being filtered overwhelms that effect. More calcium therefore leaves in the urine, a state called hypercalciuria, and this urinary calcium load is the direct link between the parathyroid glands and kidney stones.

See how urinary calcium becomes a stone

Stones form when urine is supersaturated with calcium and partners such as oxalate or phosphate. Hypercalciuria raises that saturation. High blood calcium also interferes with the kidney's ability to concentrate urine, producing polyuria, nocturia and thirst. If the patient cannot replace those losses, dehydration follows.

Dehydration matters because concentrated urine makes crystals more likely to form and grow. A patient with hyperparathyroidism can therefore enter a cycle of calcium overload, fluid loss and further stone risk. Chronic hypercalcaemia is particularly linked with stone formation, so repeated stones can be the first clue to an overactive parathyroid gland.

Thiazide diuretics are relevant here because they can raise serum calcium, which is why they are usually avoided or stopped in hypercalcaemia. If a patient with known hyperparathyroidism is newly prescribed one, the nurse should check that the prescriber is aware of the calcium history. Medication review is part of stone prevention, not only symptom treatment.

Recognise the wider pattern of high calcium

Kidney stones are one part of a broader picture often summarised as stones, bones, groans and psychiatric changes. Bone loss can lead to osteoporosis and fractures. Gastrointestinal effects include constipation, nausea and loss of appetite. Higher calcium levels can cause confusion, lethargy and, when severe, stupor or coma.

On the ECG, severe hypercalcaemia can shorten the QT interval, and patients taking digoxin face higher arrhythmia risk. Many people with primary hyperparathyroidism have mild symptoms or none and are found on routine blood tests, so the absence of complaints does not exclude kidney or bone effects.

Turn the mechanism into fluid, strain and pain actions

Encourage generous fluid intake, unless restricted for another reason, to dilute urine and reduce crystal formation. Monitor intake and output, daily weight and signs of dehydration. Patients with significant hypercalcaemia are usually volume depleted, and saline hydration is a cornerstone of treatment when prescribed. Report medicines such as thiazide diuretics, which can raise calcium.

During suspected stone passage, strain all urine so a stone can be saved for analysis, which guides prevention. Assess pain that starts in the flank and moves toward the groin, haematuria, nausea, fever and reduced urine output. Give prescribed analgesia, encourage mobility if allowed, and report fever with obstruction promptly because infection behind a blocked kidney is an emergency.

Work a hypothetical exam-style scenario

Imagine a patient with primary hyperparathyroidism awaiting surgery who reports severe left flank pain radiating to the groin, nausea and pink urine. Options are to restrict fluids to reduce pain from distension, encourage fluids within orders, strain all urine and give prescribed analgesia, encourage high-calcium foods, or discard urine samples once pain settles.

Encouraging fluids, straining urine and treating pain is best, because the presentation suggests a calcium stone driven by hypercalciuria, and a retrieved stone guides prevention. Fluid restriction concentrates urine. Deliberately increasing calcium intake is not a standard response and should follow dietitian or prescriber advice. Discarding urine loses the stone. Fever would require prompt escalation.

Sources and further reading

NIDDK: Primary Hyperparathyroidism. Parathyroid hormone effects on bone, gut and kidney, urinary calcium and kidney stones, symptoms, fluid advice and surgery.

MSD Manual Professional: Hypercalcemia. PTH actions, hypercalciuria, nephrolithiasis, concentrating defect, symptom pattern, short QT, saline hydration and thiazide avoidance.

MedlinePlus: Kidney stones. Flank-to-groin pain, blood in urine, straining urine to save the stone and fluid intake.