In patients experiencing secondary erythrocytosis while receiving both SGLT2i and testosterone, clinicians should i) determine just how sound was the original indication for testosterone therapy (e.g. survivor of childhood cancer versus obese man with mild sexual symptoms and slightly low T level without anaemia or raised LH), ii) evaluate and manage all modifiable risk factors, which should include the aggressive treatment of incident hypertension with vasodilator drugs, and iii) adjust the dose and delivery route, before considering complete discontinuation of treatment. The gene discussed is PLOD1; the disease is anemia (phenotype).