The Calcium Connection — summary-day capstone

Before the patient: one framework, several connected systems

This fictional summary-day capstone integrates electrolytes, CKD, AKI, stones, monoclonal proteins and nephrotic syndrome. Allow about 22 minutes. Discussion prompts are ungraded and supplement the original 30 cases.

Four urgent assessment domains: heart, brain, breathing and perfusion, and kidney/metabolic threats; stabilize and investigate in parallel, then reassess. — · Download PNG · Download Markdown · Read text and evidence
Name the threat, begin indicated treatment, investigate in parallel, then reassess.

1 · Approach

Assess urgency and volume. Confirm the abnormality. Compare current kidney function with a baseline.

2 · Findings

Use blood, urine and imaging together. A prior diagnosis does not explain every new abnormality.

3 · Interpretation

Let PTH organize the calcium workup. Compare albumin with total urine protein.

4 · Treatment and synthesis

Correct immediate threats, identify the lesion and clone, and reassess organ response.

Urgent-threat framework across the week · Opening lecture: kidney function and the skeleton key

A creatinine rise in a patient with CKD and prior stones

A 64-year-old woman has one week of worsening thirst, frequent urination, constipation, poor intake and new slowed thinking. She also reports several weeks of back discomfort. She is not taking calcium supplements, high-dose vitamin D, lithium or a thiazide.

Her creatinine has been 1.2 mg/dL, with a reported eGFR near 50 mL/min/1.73 m² and UACR 65 mg/g, for more than six months. She passed a calcium oxalate stone two years ago. She took ibuprofen for her recent back pain.

She is afebrile, heart rate 108/min and BP 102/64 mmHg. Mucous membranes are dry; lungs are clear and there is no edema. She is slow to answer but follows commands.

Treat the urgent problem while choosing the next tests

Initial findings in this fictional adult case. Reference intervals are illustrative and laboratory-specific.
Test / finding	Result	Teaching reference / context
Total calcium / ionized calcium	14.8 mg/dL / 1.85 mmol/L	8.6–10.2 / 1.12–1.32
Albumin / total serum protein	3.6 / 9.2 g/dL	Albumin 3.5–5.0; protein 6.4–8.3
Creatinine / BUN	3.0 / 58 mg/dL	Creatinine was 1.2 one week ago
Na / K / bicarbonate	146 / 3.2 / 25 mmol/L	Assess water balance, potassium deficit and acid–base status
Phosphate / alkaline phosphatase	4.7 mg/dL / 96 U/L	2.5–4.5 / 40–129; ALP is normal
Hemoglobin	9.4 g/dL	Previously 12.1 g/dL
Urinalysis	1+ protein; 0–2 RBC/hpf; no pyuria	Dipstick mainly detects albumin
Spot UPCR / UACR	3.8 g/g / 180 mg/g	Total protein versus albumin: convert to matching units
Kidney/bladder ultrasound	Small nonobstructing stones; no hydronephrosis or bladder retention	Stones are present, but obstruction has not been demonstrated

Pause and commit

What begins now, and what can be investigated in parallel? Is the proteinuria necessarily nephrotic syndrome?

Discuss first, then reveal the teaching explanation

Give isotonic saline for documented volume depletion with repeated assessment of BP, breathing and urine output. Start calcium-lowering treatment under the acute-care team; severe suspected malignancy-associated hypercalcemia may need calcitonin plus a longer-acting antiresorptive. Stop the NSAID. Send PTH and directed studies without delaying stabilization.

UPCR 3.8 g/g is nephrotic-range total protein, but UACR 180 mg/g is only 0.18 g/g. Albumin accounts for roughly 5% of measured protein on this sample. The patient has no edema and albumin is 3.6: this is not the usual albumin-heavy nephrotic syndrome. Consider nonalbumin protein, including light chains. The ratio is a clue, not a biopsy diagnosis.

AKI evaluation lecture · Stone and obstruction case · Fluid choice and reassessment

Use the existing calcium chart: which mechanism fits?

Read the seven results as one physiologic pattern, after identifying the urgent problem.
Requested marker	Patient result	Reference / interpretation task
Ca	14.8 mg/dL; ionized 1.85 mmol/L	Confirmed hypercalcemia
PO₄	4.7 mg/dL	Mildly high during AKI; do not use phosphate alone to name the cause
Alk Phos	96 U/L	Within the stated reference interval
1,25(OH)₂ vitamin D	12 pg/mL	18–72; low
25(OH) vitamin D	31 ng/mL	Within this laboratory’s 20–50 interval
PTH	6 pg/mL	15–65; suppressed
PTHrP	<2.0 pmol/L	Not elevated; this assay’s upper limit is 4.2

Six common hypercalcemia mechanisms compared across calcium, phosphate, alkaline phosphatase, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, PTH and PTHrP, with caveats for kidney dysfunction and normal ALP in myeloma. — · Download PNG · Download Markdown · Read text and evidence
Ca, phosphate, alkaline phosphatase, both vitamin D metabolites, PTH and PTHrP.

Typical patterns, not diagnostic requirements. N = the laboratory reference interval; ↑ = increased; ↓ = decreased.
Mechanism	Ca	PO₄	Alk Phos	1,25(OH)₂D	25(OH)D	PTH	PTHrP	Interpretation
Primary hyperparathyroidism	↑	↓ or N	N or ↑	N or ↑	Variable	↑ or inappropriately N	Not elevated	PTH should be suppressed by high calcium; check urine calcium in the appropriate setting.
PTHrP-mediated malignancy	↑	↓ or N	Variable	↓ or N	Variable	↓	↑	PTHrP mimics some PTH effects. An abnormal SPEP is not required.
Calcitriol-mediated disease	↑	N or ↑	Variable	↑	N or ↓	↓	Usually not elevated	Consider lymphoma or granulomatous disease; the lab pattern does not identify which.
Vitamin D₂/D₃ excess	↑	N or ↑	N or ↓	N or ↑	Markedly ↑	↓	Not elevated	Excess nutritional vitamin D raises 25(OH)D; active-vitamin-D medications are a different exposure.
Osteolytic malignancy / myeloma	↑	Variable	Variable; often N in myeloma	↓ or N	Variable	↓	Usually not elevated	ALP can remain normal despite lytic lesions; evaluate monoclonal protein when indicated.
Calcium–alkali syndrome	↑	↓ or N; affected by kidney function/intake	Usually N	↓ or N	Variable	↓	Not elevated	Calcium/alkali exposure, alkalosis and AKI; medication history matters.
Tertiary hyperparathyroidism	↑	Often ↑ in advanced CKD; may fall after transplant	Variable	Variable; often low in advanced CKD	Variable	Markedly ↑	Not elevated	Longstanding secondary HPT becomes autonomous; CKD alone does not prove this diagnosis.
Familial hypocalciuric hypercalcemia	Usually mildly ↑	N or ↓	Usually N	Variable	Variable	N or mildly ↑	Not elevated	Lifelong/familial pattern and relative hypocalciuria; CKD, low vitamin D and thiazides confound urine calcium.

Change one mechanism: three quick counterfactuals

PTH 60 pg/mL with calcium 14.8: a reference-range PTH is inappropriately unsuppressed; investigate PTH-dependent disease.
Suppressed PTH with high PTHrP: consider humoral hypercalcemia of malignancy, as in the earlier renal-mass case.
Suppressed PTH, high 1,25(OH)₂D and normal/low 25(OH)D: consider calcitriol-mediated disease such as lymphoma or granulomatous disease. Very high 25(OH)D instead directs attention to nutritional vitamin D excess.

Full hypercalcemia lecture and laboratory chart · Revisit Case 12: the renal mass and PTHrP pathway

The results identify myeloma; the kidney injury can still be mixed

Serum immunofixation identifies an IgG-kappa monoclonal protein; urine immunofixation identifies monoclonal kappa light chains. Serum free kappa is 2,400 mg/L and lambda 18 mg/L. Directed imaging shows lytic lesions. Bone marrow examination later shows 30% clonal plasma cells. These findings establish multiple myeloma with attributable myeloma-defining disease; a positive protein screen alone would not.

Kidney synthesis: volume depletion and hypercalcemia can reduce filtration, NSAID exposure can worsen perfusion, and the marked light-chain burden with mostly nonalbumin proteinuria raises concern for cast nephropathy. Cast injury is strongly suspected, not proven by the dipstick or FLC result alone. Nephrology decides whether tissue evaluation is needed, especially if the presentation or course is atypical.

Treatment priorities, not a patient-specific order set.
Time / goal	Teaching action
Now: stabilize	Monitored care; isotonic saline for volume depletion with repeated reassessment. Follow calcium, potassium, magnesium, phosphate, urine output and respiratory status.
Bridge: lower calcium	Calcitonin can provide a relatively rapid bridge; limit treatment to 48–72 hours because of tachyphylaxis.
Sustain: control hypercalcemia	For malignancy-associated hypercalcemia, select an IV bisphosphonate or denosumab with attention to kidney function and later hypocalcemia risk. These are not instant substitutes for stabilization.
Treat the cause	Urgent hematology/nephrology coordination for effective myeloma-directed treatment. Lowering calcium alone does not stop light-chain production.
Escalate and reassess	Dialysis is considered for refractory severe problems or when the clinical situation limits other treatment; neither creatinine nor FLC concentration alone is an automatic trigger. Routine loop diuretics are not used to force calcium excretion in a volume-depleted patient.

Full student guide: monoclonal gammopathy and kidney disease

A second protein pattern: nephrotic syndrome from AL amyloid

Compare a second fictional patient: progressive edema, serum albumin 2.1 g/dL, creatinine 1.6 mg/dL, calcium 9.4 mg/dL, UPCR 6.0 g/g and UACR 5,200 mg/g. Monoclonal studies identify a small lambda-producing clone. There are no lytic lesions.

Pause and commit

Why is this different from the first patient, and what establishes AL amyloidosis?

Discuss first, then reveal the teaching explanation

UACR 5,200 mg/g equals 5.2 g/g: albumin is most of the 6.0 g/g total protein. With hypoalbuminemia and edema, this is a glomerular nephrotic pattern. It suggests a different kidney lesion, but does not by itself prove amyloid. In this fictional comparison, tissue biopsy demonstrates Congo-red-positive deposits and proteomic typing identifies AL-lambda amyloid. Biopsy site is chosen clinically; a kidney biopsy is not mandatory if an appropriate alternative tissue establishes and types amyloid.

A small clone can cause major organ injury. Assess cardiac and other organ involvement, which affects treatment tolerance and fluid management. AL amyloidosis is not synonymous with multiple myeloma, and amyloid alone does not ordinarily explain hypercalcemia or lytic bone lesions.

Comparison of light-chain cast nephropathy with predominantly nonalbumin proteinuria and AKI, and renal AL amyloidosis with albumin-heavy nephrotic syndrome; tissue diagnosis and amyloid typing distinguish lesions. — · Download PNG · Download Markdown · Read text and evidence
Tubular light-chain cast injury versus glomerular AL amyloid deposition.

Keep LCDD and MGRS distinct

Light-chain deposition disease (LCDD) has nonamyloid, nonfibrillar deposits and may involve glomerular, tubular and vascular basement membranes. It is another possible cause of proteinuria and kidney dysfunction. Congo-red negativity alone does not establish LCDD; light microscopy, immunofluorescence and electron microscopy define the lesion.

MGRS describes kidney injury attributable to a nephrotoxic monoclonal immunoglobulin from a clone that does not otherwise meet established hematologic treatment criteria. It is not a fixed marrow-percentage rule or a synonym for every kidney problem in a patient with an M-protein. Myeloma-associated cast nephropathy belongs to myeloma-related kidney disease.

Tests are complementary: SPEP/UPEP, immunofixation and serum FLC answer related questions. CKD affects both absolute FLC levels and ratio interpretation; use assay-appropriate reference intervals. A normal ratio does not by itself exclude AL or every MGRS lesion. MASS-FIX may identify a circulating monoclonal protein where available; it does not replace typing amyloid deposits in tissue.

Monoclonal kidney disease student guide · Amyloidosis and myeloma student guide · Edema lecture and diagnostic pathway · Compare Case 24: two nephrotic presentations

Electrolytes, CKD, AKI, stones and proteins: explain the connections

Use the same blood–urine–imaging framework across the week.
System	How it fits this case
Electrolytes	Hypercalcemia explains several symptoms and can impair concentrating ability. Polyuria and poor intake contribute to water and potassium deficits. Phosphate must be read in the context of AKI.
CKD	Documented chronic G3a/A2 disease establishes reduced reserve. It does not explain the new creatinine rise or newly heavy nonalbumin protein excretion.
AKI	Volume depletion, hypercalcemic effects, NSAID exposure and possible cast injury can coexist. An unstable creatinine makes routine eGFR a poor estimate of current filtration.
Stones	Hypercalciuria can promote calcium stones, but an old stone does not establish the present calcium mechanism. Nonobstructing stones do not explain postrenal AKI; obstruction must be assessed.
Urine protein	UPCR and UACR measure different things. Nonalbumin-heavy proteinuria points toward a tubular/overflow pattern; albumin-heavy proteinuria with edema and low albumin suggests nephrotic glomerular disease.
Myeloma versus AL	Myeloma can cause hypercalcemia, anemia, lytic lesions and cast injury. AL amyloid can cause nephrotic syndrome from a small clone; tissue confirmation and typing remain essential.
Treatment	Stabilize immediate threats, treat the cause and track recovery. A calcium improvement, a falling light-chain level and a kidney response are related but separate endpoints.

Exit discussion

Name the threat that could not wait for the full workup.
Explain why normal ALP and non-elevated PTHrP did not exclude myeloma.
Convert UACR to the same units as UPCR and explain what the mismatch suggests.
State what proves amyloid, what types it and what identifies the clone.
Name one finding that would change fluids, drainage or dialysis planning.

Return to Day 5 · Bring the lecture to the bedside · Visual library: summary-day figures

Clinical sources and further reading