Which ONE of the following is the next best step to manage this patient?
Isotonic intravenous fluids
Correct! In a patient with hypercalcemia without evidence of volume overload, the first step is volume resuscitation with isotonic fluid. If the patient develops evidence of overload, loop diuretics can be given with intravenous fluids.
Oops! Try again, there’s a better initial step for this case.
Ouch! We still have some work to do before we might think about a kidney biopsy. Try again!
We may reach for a bisphosphonate later, but there’s a better option for us to start with.
The mechanism of action of calcitonin may be of some benefit here, but this is not the best way to begin the management of this patient.
The following day, the patient’s ionized calcium remains elevated at 2.4 mmol/L. To uncover the etiology of the hypercalcemia, what’s the next best test (more than one may be correct!)
Serum intact parathyroid hormone (iPTH)
Correct! Checking the iPTH level is the first step to solving any case of hypercalcemia. The iPTH is undetectable.
Complement levels (C3, C4)
This is not the highest yield test here, as we don’t have any evidence of complement mediated disease so far. Try again!
Ouch! There are less invasive tests that are likely to provide more information about this patient’s hypercalcemia.
Repeat urine sodium
The urine sodium may be low in hypercalcemic patients due to vasoconstriction of the blood vessels and hypovolemia, but won’t help us differentiate between causes of hypercalcemia.
Pick again! Uric acid levels are less likely to help us figure out why this patient is hypercalcemic.
Pick again! Urine citrate levels may be helpful in a patient with nephrolithiasis, but probably won’t be of use here.
Ventilation/perfusion (V/Q) scan
A V/Q scan may useful if there is clinical suspicion for a pulmonary embolism, but won’t help us narrow down a differential for hypercalcemia.
Serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE)
Great! A patient with hypercalcemia and acute kidney injury should raise suspicion for a monoclonal gammopathy. The SPEP reveals a monoclonal protein (“M” spike) and the IFE identifies it as an immunoglobulin G (IgG).
Parathyroid hormone related protein (PTH-rP)
Good choice. Elevated PTH-rP levels might suggest humoral hypercalcemia. Here, it’s undetectable
Calcitriol (1,25 OH Vitamin D)
Yes! Elevated calcitriol levels might narrow down our hypercalcemia differential diagnosis. Here, it’s slightly below the lower limit of normal (10 pg/mL)
Bronchoscopy with transbronchial biopsy
Careful! A bronschoscopy is an invasive test that doesn’t seem to be indicated yet here. Choose again!
With that additional information, what’s your final diagnosis?
Acute interstitial nephritis
Small cell lung cancer
Click here once you are confident in your final diagnosis!