16.3 Hematopoietic and Immune Disorders

The current FNP-BC Test Content Outline scores Hematopoietic and Immune as two of the 13 body systems and lists immunologic agents among the official drug-agent classes. Domain II is the smear-and-serology logic. Domain IV is the epinephrine, the iron, the HIV test, and the referral you do not delay. Allergic rhinitis is already taught in HEENT (Section 15.1). This section is the blood, the immune emergency, and the node you should not watch for six months.

Anemia: MCV first, then the right second test

Do not treat a hemoglobin number as a disease name. Start with the mean corpuscular volume (MCV) and a reticulocyte count that tells you whether the marrow is answering.

• Microcytic (MCV <80 fL): iron deficiency, thalassemia trait, and some anemia of chronic disease. Next tests: ferritin, TIBC (or transferrin), serum iron. Iron deficiency is low ferritin, high TIBC, low iron, and often a high RDW. Thalassemia trait is a long-standing very low MCV with a relatively preserved hemoglobin, a normal or high ferritin, and a family or ancestry story — confirm with hemoglobin electrophoresis, do not iron-load the patient. Anemia of chronic disease often shows a normal or high ferritin and a low TIBC.
• Normocytic (MCV 80–100): acute blood loss, hemolysis, CKD, mixed iron-plus-B12, early iron deficiency, and marrow problems. A high reticulocyte count points to loss or hemolysis. A low reticulocyte count points to underproduction — look at creatinine, TSH, and the rest of the CBC.
• Macrocytic (MCV >100): B12 and folate deficiency, alcohol, some medicines (hydroxyurea, zidovudine, methotrexate), and myelodysplasia in older adults. B12 deficiency can add neuropathy and glossitis; folate usually does not. Recheck medicines before you assume MDS.

Iron deficiency is a symptom. In a menstruating adolescent or premenopausal adult, quantify menstrual blood and diet, but still think twice if the anemia is severe or the story is thin. In a man or a postmenopausal woman, plan a gastrointestinal evaluation for occult bleed — including colorectal neoplasia — rather than refilling ferrous sulfate for a year. GU bleeding and repeated blood donation also count. Intravenous iron is for intolerance, malabsorption, or ongoing loss you cannot keep up with, not the first tablet trial in an otherwise well adult.

A 67-year-old man with fatigue, MCV 72, and ferritin 8 does not have “low iron of aging.” He has a bleed you have not found.

Sickle cell, ITP, clot, and bleed

Sickle cell disease primary care is prevention plus disposition. Children need penicillin prophylaxis in the early years (classically at least through age 5, following hematology), and everyone needs vaccines that prevent encapsulated-organism disaster: pneumococcal, meningococcal, Haemophilus influenzae type b as indicated, plus annual influenza. Hydroxyurea reduces crises and is usually comanaged with hematology — do not freelance a start-stop plan from a sports-physical slot.

Uncomplicated vaso-occlusive pain in a person who knows their typical crisis can be treated with hydration, heat, and an agreed analgesia plan. Emergency-department red flags: fever (functional asplenia makes bacteremia an emergency), chest pain or hypoxia (acute chest syndrome), focal neurologic change (stroke), priapism, severe abdominal swelling (sequestration), or a sudden drop in hemoglobin after a viral illness (parvovirus aplastic crisis). Those are not “try another oxycodone at home” visits.

ITP (immune thrombocytopenia) is isolated low platelets with a normal hemoglobin and white count after you exclude drugs, HIV, hepatitis C, and other cytopenias. Children often follow a viral illness and recover. Adults more often need hematology. Red flags that are not simple ITP: wet purpura (oral blood blisters), mucosal bleeding, very low platelets with active bleed, fever, lymphadenopathy, or another cell line down. Those patients go to the emergency department or same-day hematology. Easy bruising on a stable 90,000 platelet count after a viral week is a different visit from gingival bleeding and a platelet count of 4,000.

Thrombosis versus bleed is a planning skill. Do not start a DOAC in clinic because a calf “looks like a clot” if the patient is already pouring blood from a duodenal ulcer. Do not withhold indicated anticoagulation after a confirmed PE because a bruise from a blood-pressure cuff frightened the family. Unprovoked VTE in a young adult or recurrent miscarriage raises antiphospholipid and other thrombophilia questions you will usually work up with specialty, not with a twelve-gene panel on the first afternoon. NSAIDs plus an anticoagulant plus a prior GI bleed is a hemorrhage you can see coming.

HIV screening, PrEP, and immunologic emergencies

USPSTF recommends HIV screening in adolescents and adults aged 15–65 (and younger or older people at increased risk), plus screening in pregnancy. A one-time test is not enough when risk continues. Use a fourth-generation antigen/antibody test. A new positive is a same-week confirmatory and linkage visit, not a voicemail on Friday at 4:55 p.m.

PrEP (pre-exposure prophylaxis) is for people at substantial ongoing HIV risk — for example a partner with HIV who is not durably suppressed, condomless sex in a high-prevalence network, or injection-drug equipment sharing. Do not invent a 2026 brand-by-brand algorithm if the stem does not hand you a labeled product. Teach the indication and the safety scaffold that every regimen shares:

1. Documented HIV-negative test immediately before start (starting PrEP in undiagnosed HIV risks resistance).
2. Baseline creatinine / eGFR (tenofovir-containing orals need a kidney you can defend).
3. Hepatitis B status (some orals treat HBV; stopping them can flare hepatitis B).
4. STI screening and pregnancy testing when relevant.
5. Follow-up about every 3 months: repeat HIV test, adherence, STI screen, and interval renal monitoring per the regimen.

If the patient cannot return, PrEP is not a one-bottle souvenir. Cabotegravir and oral combinations exist; the exam tests the framework, not a memorized 2026 market-share chart.

Anaphylaxis is an immunologic-drug Implementation item. First-line is intramuscular epinephrine in the mid-anterolateral thigh, then EMS. Airway, wheeze, hypotension, or multi-system involvement (skin plus gut plus respiratory) is anaphylaxis even without shock. Antihistamines and steroids are adjuncts. They are not the first syringe. Send every at-risk patient out with an epinephrine autoinjector and a written action plan. Do not re-teach the entire allergic-rhinitis ladder here — that is HEENT.

Autoimmune disease in this chapter is the overlap, not a second rheumatology textbook. Rheumatoid arthritis (symmetric small-joint inflammatory arthritis, morning stiffness, RF/CCP conceptually) is diagnosed and DMARD-started with rheumatology; the FNP recognizes it, screens for infection before immunosuppression, and keeps vaccines current. Do not start a biologic because a single ANA came back at 1:40. Immunologic agents (systemic steroids, DMARDs, biologics) are high-harm classes: infection, hepatitis B reactivation, and live-vaccine mistakes belong on your checklist when you comanage.

Immunodeficiency is recurrent serious infections — repeated pneumonias, deep abscesses, opportunistic organisms, poor growth in a child, or an adult who never clears sinus and lung disease. That is not “three colds in a winter.” Refer to immunology; do not give a twelfth antibiotic course as the only plan.

Lymphadenopathy: watch, image, or biopsy

Most nodes after a pharyngitis or a cat scratch are reactive. Watch localized, soft, mobile, tender nodes for about 3–4 weeks if the patient is well and a source is obvious. Image or refer for biopsy when a node is hard or fixed, larger than about 2 cm and growing, supraclavicular, persistent beyond a month without a source, or accompanied by B symptoms (fever, night sweats, weight loss), unexplained cytopenias, or a hard liver or spleen. Generalized adenopathy is HIV, EBV, lymphoma, syphilis, SLE, or a drug until you sort it — not “allergies.”

FNP traps: iron for a year in a man with microcytic anemia and no colonoscopy plan; calling every sickle pain a home day when fever and chest pain are present; labeling pancytopenia as ITP; starting PrEP without an HIV test; treating anaphylaxis with diphenhydramine first; and watching a rock-hard supraclavicular node through two school semesters.