Case presentation

This retrospective case series included all patients who developed severe iodinated contrast-induced anaphylactic shock following contrast-enhanced CT examinations at our institution between January 2024 and December 2025.

Case 1: breast cancer patient with no prior allergy history

An 88-year-old woman presented with a two-month history of a left breast lump. Clinical examination revealed notable skin tethering with mild nipple retraction. Imaging for further investigation was performed: bilateral mammogram and breast ultrasound (September 2024) demonstrated two highly suspicious left breast lesions. Breast MRI (September 2024) confirmed multiple suspicious masses and multiple left axillary lymph nodes.

Ultrasound-guided core biopsy (September 2024) confirmed invasive ductal carcinoma (no special type), with axillary nodal macrometastasis. A staging contrast-enhanced CT of the thorax, abdomen, and pelvis was subsequently scheduled.

Preprocedural assessment was unremarkable. The patient reported no history of allergies to food or medication, no prior contrast exposure, and no other comorbidities. Baseline creatinine was found to be 68 µmol/L (reference range: 62-106 µmol/L). Vital signs prior to the procedure were within normal limits (heart rate (HR), 68 bpm; blood pressure (BP), 121/74 mmHg; peripheral oxygen saturation (SpO₂), 96% on room air). A 22G intravenous (IV) cannula was placed in the right dorsal metacarpal vein. The CT scan commenced at 09:28 with IV administration of 100 mL iohexol (Omnipaque 300 mg/mL) at 2.5 mL/s.

Although the exact interval between contrast administration and symptom onset was not documented, within minutes of contrast injection, the patient developed nausea, vomiting, and coughing. Oxygen saturation dropped to 86%, and HR increased to 130 bpm. The contrast injection was stopped, and the rapid response team (RRT) was activated at 09:45. The patient was placed in the left lateral position, and oxygen was administered via a non-rebreather mask. On RRT arrival (09:48), vital signs were HR 124 bpm, BP 157/101 mmHg, and SpO₂ 100% on high-flow oxygen. IV hydrocortisone 200 mg and diphenhydramine 50 mg were administered immediately.

The patient was subsequently transferred to the recovery room. BP rapidly became unrecordable with only faint central pulses; the level of consciousness deteriorated. Epinephrine 0.5 mg was given intramuscularly at 09:55, and IV fluid resuscitation was initiated.

By 10:00, BP had improved to 91/57 mmHg with SpO₂ 100%; the patient began to respond. A further dose of epinephrine 0.1 mg IV was administered at 10:10 prior to transfer to the intensive care unit (ICU) at 10:19. ICU admission was undertaken because of profound hypotension requiring repeated epinephrine administration and close hemodynamic monitoring following cardiovascular collapse.

In the ICU, the patient was alert and spontaneously breathing on room air. Neurological status was intact (Glasgow Coma Scale (GCS), 15/15). Laboratory investigations demonstrated reactive leukocytosis, with the white blood cell count increasing from 5.7 x 103/ µL before CT scan to 26.6 × 10³/µL (reference range: 4.0-11.0 × 10³/µL) and mild anemia of hemoglobin 9.9 g/dL (reference range: 12.0-15.5 g/dL), consistent with the acute event and underlying malignancy; an elevated serum tryptase of 82.7 mcg/L (reference range: <11.4 mcg/L), supporting the diagnosis of anaphylaxis. Venous blood gas analysis demonstrated a mildly alkalotic pH of 7.46 (reference range: 7.32-7.43) with an elevated lactate of 4.6 mmol/L (reference range: 0.5-2.2 mmol/L). Renal and hepatic parameters were normal.

Over the subsequent 24 hours, hemodynamics gradually normalized (Table 1). The patient was maintained on corticosteroids, antihistamines, IV fluids, and electrolyte replacement. She was discharged after 24 hours with a short course of prednisolone and antihistamines and was referred to the immunology clinic for further evaluation.

Time | HR (bpm) | SBP (mmHg) | DBP (mmHg) | SpO₂ (%) | O₂ therapy | RR (/minute)
08:54 | 68 | 121 | 74 | 96 | None | Not recorded
09:45 (RRT activated) | 130 | 110 | 71 | 86 | NRBM | Not recorded
09:48 (RRT arrival) | 124 | 157 | 101 | 100 | NRBM | 25
10:00 | 149 | 91 | 57 | 100 | NRBM | Not recorded
13:00 | 72 | 92 | 61 | 98 | Room air | 17
15:00 | 68 | 101 | 57 | 98 | Room air | 17
20:00 | 84 | 106 | 64 | 97 | Room air | 18
07:00 (+24 hours) | 76 | 118 | 65 | 100 | Room air | 21

Case 2: cardiovascular patient with penicillin allergy

The second patient was a 59-year-old man with a background of hypertension, chronic obstructive pulmonary disease (COPD), and ischemic heart disease (IHD), with a documented penicillin allergy characterized by generalized pruritus and gastrointestinal symptoms. He had no prior history of hypersensitivity reaction to contrast media. He was admitted in November 2025, for contrast CT-guided cardiac evaluation. Preprocedural assessment was unremarkable, with baseline vitals demonstrating a BP of 136/83 and a saturation of 96% on room air. Iodixanol (Visipaque 320 mg/mL) was selected as the contrast agent. IV access was established through the right antecubital vein using a 22G cannula, and 90 mL of contrast was administered at 2.5 mL/s.

During contrast administration, a reaction was noted, where the patient developed an erythematous rash with generalized skin flushing and swelling of the lips and oral mucosa. He reported dizziness and tingling in his fingers and was unable to maintain a semiupright position. Oxygen saturation decreased to 94% on room air, and BP fell to 105/58 mmHg. Although the exact interval between symptom onset and treatment was not documented, the contrast injection was stopped, and IV hydrocortisone 200 mg and diphenhydramine 50 mg were administered without delay.

The patient's condition deteriorated with progressive hoarseness of voice, worsening dyspnea, and even further hemodynamic compromise; BP declined to 71/38 mmHg. In response, epinephrine 0.5 mg was administered intramuscularly into the vastus lateralis. The patient was transferred to the emergency department for further stabilization. At the time of transfer, the airway was patent, and the patient was phonating without stridor; lip edema had resolved. Supplemental oxygen was administered, IV fluid resuscitation was initiated, and the patient was stabilized with continued supportive management. He did not require ICU admission (Table 2). Following stabilization in the emergency department, the patient remained hemodynamically stable with cutaneous symptoms over the subsequent hours. Laboratory investigations demonstrated reactive leukocytosis, with the white blood cell count increasing from 9.0 to 22.0 × 10³/µL (reference range: 4.0-11.0 × 10³/µL). Venous blood gas analysis showed a normal pH of 7.40 (reference range: 7.32-7.43) and a normal lactate of 1.4 mmol/L (reference range: 0.5-2.2 mmol/L). Serum tryptase was not obtained or documented during the acute event. He was discharged with a short course of oral corticosteroids and antihistamines, advised to avoid ICM in future imaging unless deemed clinically essential, and referral to allergy/immunology was recommended.

Time | HR (bpm) | SBP (mmHg) | DBP (mmHg) | SpO₂ (%) | Intervention
Baseline | 74 | 136 | 83 | 96% RA | IV access established
During contrast injection | 90 | 105 | 58 | 94% | Hydrocortisone 200 mg IV + Diphenhydramine 50 mg + NRBM
Postinjection (deterioration) | 99 | 71 | 38 | Declining | Epinephrine 0.5 mg IM; emergency transfer + NRBM

Case 3: breast cancer patient with confirmed elevated serum tryptase

The third patient was a 47-year-old woman with an identical oncological background to Case 1: left breast invasive ductal carcinoma confirmed on core biopsy with axillary nodal macrometastasis. Staging contrast-enhanced CT of the thorax, abdomen, and pelvis was requested (March 20, 2025).

Preprocedure screening showed no previous history of contrast reactions, no known drug or food allergies, and no active comorbidities. The patient had not previously received ICM for any imaging study. Baseline hemodynamics and renal function were normal. The CT scan commenced with IV administration of 100 mL iohexol (Omnipaque 300 mg/mL) at 2.5 mL/s.

Shortly after the commencement of contrast injection, the patient became acutely unwell with nausea and vomiting. Although the exact interval between symptom onset and treatment was not documented, the contrast injection was stopped. The RRT was activated at 09:45 and arrived at 09:49. At that time, vital signs were as follows: HR 125 bpm, BP 80/50 mmHg, SpO₂ 86% on nasal cannula, and RR 25/minute. Chest auscultation demonstrated bilateral equal air entry without wheeze. IV hydrocortisone 100 mg and diphenhydramine 50 mg were administered. No cutaneous manifestations were observed; gastrointestinal symptoms predominated throughout the reaction.

The patient was moved from the CT scanner to the recovery room. Rapid deterioration occurred instantly, with the BP becoming unrecordable; the carotid pulse was present, but the radial pulse was absent; and the patient became unarousable. Epinephrine 0.5 mg was administered intramuscularly, and IV Ringer's lactate was commenced as a bolus. Neurological and hemodynamic improvement was evident within five minutes, with BP recovering to 90 mmHg systolic and SpO₂ returning to 100% on 15 L/minute oxygen. The patient began opening her eyes and making sounds but remained agitated.

A further dose of IV epinephrine (0.1 mg) was administered because of persistent hemodynamic instability and the severity of the anaphylactic reaction. Given the need for repeated epinephrine administration, the patient was transferred to the ICU for close hemodynamic monitoring and observation. On arrival to the ICU, hemodynamics and GCS steadily improved without the need for further vasopressors. Serum tryptase, measured in the acute phase, was elevated at 40.30 mcg/L (reference range: <11.4 mcg/L), providing biochemical confirmation of mast cell activation consistent with anaphylaxis. Venous blood gas analysis demonstrated a normal pH of 7.38 (reference range: 7.32-7.43) and a lactate of 1.7 mmol/L(reference range: 0.5-2.2 mmol/L). These findings indicated preserved acid-base status without significant tissue hypoperfusion despite the patient's profound hemodynamic instability. Prior to discharge, the patient was advised to avoid future iodinated contrast exposure unless clinically essential, and a formal allergy/immunology referral was made. The clinical events and parameters for this case are summarized in Table 3.

Time | HR (bpm) | SBP (mmHg) | DBP (mmHg) | SpO₂ (%) | Intervention
Baseline | 79 | 131 | 74 | 99% | -
09:45 (RRT activated) | 125 | 110 | 69 | 85% | Lateral position, O₂
09:49 (RRT arrival) | 125 | 80 | 50 | 86% | Hydrocortisone 100 mg + Diphenhydramine 50 mg IV+ Nasal cannula for O2
Post RRT | 140 | Unrecordable | Unrecordable | 100% 15L O₂ | Epinephrine 0.5 mg IM; Ringer's stat + NRBM
<5 minute postadrenaline | Not recorded | 90 | Not recorded | 100% | NRBM
Pretransfer | 149 | 96 | 54 | 100% | Epinephrine 0.1 mg IV+ NRBM
ICU arrival | 109 | 110 | 55 | 100% | No further adrenaline required

Results

All three patients developed anaphylactic shock following contrast administration, with no prior history of contrast hypersensitivity. Onset was rapid in all cases, occurring during or immediately after the injection. The clinical spectrum ranged from cutaneous and hemodynamic compromise (Case 2) to cardiovascular collapse with loss of consciousness (Cases 1 and 3). Epinephrine was required in all three cases, and ICU admission was necessary in two. All patients survived and were discharged without permanent sequelae. Table 4 provides a comparative overview, and the corresponding clinical management algorithm for suspected iodinated contrast-induced anaphylaxis is summarized in Figure 1.

Feature | Case 1 | Case 2 | Case 3
Age/sex | 88/female | 59/male | 47/female
Underlying condition | Breast cancer (IDC) | HTN, COPD, IHD | Breast cancer (IDC)
Known contrast allergy | No | No | No
Known drug or food allergy | None | Yes, drug (penicillin) | None
Contrast agent | Iohexol (Omnipaque 300) | Iodixanol (Visipaque 320) | Iohexol (Omnipaque 300)
Volume/rate | 100 mL/2.5 mL/s | 90 mL/2.5 mL/s | 100 mL/2.5 mL/s
Presenting features | Vomiting, ↓SpO₂, ↓LOC, hypotension | Rash, angioedema, dizziness, ↓SpO₂, hoarseness, hypotension | Vomiting, ↓LOC, hypotension
Lowest recorded BP | Unrecordable | 71/38 mmHg | Unrecordable
Lowest SpO₂ | 86% | 94% | 85%
Contrast stopped | Yes | Yes | Yes
Oxygen and IV fluids | Yes | Yes | Yes
IM epinephrine first line and route | 0.5 mg IM; 0.1 mg IV | 0.5 mg IM | 0.5 mg IM; 0.1 mg IV
ICU admission | Yes | No (emergency transfer) | Yes
Tryptase level | 82.7 mcg/L (elevated) (reference: <11.4) | Not documented | 40.30 mcg/L (elevated) (reference: <11.4)
Outcome | Full recovery; ICU stabilization | Full recovery; stabilized in ED, no ICU admission required | Full recovery; ICU stabilization
Allergy referral | Yes | Recommended | Yes

Figure 1: Clinical management algorithm for suspected iodinated contrast-induced anaphylaxisCV: cardiovascular; IM: intramuscular; IV: intravenous; ICU: intensive care unit; ABCDE: Airway, Breathing, Circulation, Disability, and Exposure