Atypical HELLP Syndrome Criteria
Neither ACOG, RCOG, nor NICE have established formal diagnostic criteria specifically for "atypical HELLP syndrome" in their official guidelines. The term "atypical HELLP" is used in clinical literature to describe cases where hypertension develops late or after laboratory abnormalities appear, but this is not a formally recognized diagnostic category by these major guideline organizations.
Understanding the Clinical Entity
The evidence provided consists primarily of older case reports and observational studies 1 from 1991 that describe HELLP syndrome management but do not define "atypical" criteria. More recent research 2 describes atypical HELLP as cases where:
- Hypertension develops after laboratory abnormalities (elevated liver enzymes or decreased platelets)
- Patients may present with nonspecific symptoms (dizziness, nausea, vomiting) before hypertension appears
- The classic triad of HELLP is present, but the temporal sequence differs from typical presentations
Standard HELLP Diagnostic Criteria
Since formal "atypical" criteria don't exist from ACOG/RCOG/NICE, clinicians should use the established HELLP diagnostic criteria 3, 4:
Tennessee Classification System:
- Hemolysis with LDH >600 U/L
- AST ≥70 U/L
- Platelets <100 × 10⁹/L
Mississippi Triple-Class System:
- Further classifies by nadir platelet counts
- Recognizes partial HELLP syndrome variants
Clinical Implications
The absence of hypertension does not exclude HELLP syndrome 2. When you encounter:
- Elevated liver enzymes
- Thrombocytopenia
- Evidence of hemolysis
- Without concurrent hypertension
You should still consider HELLP syndrome and manage accordingly, even if hypertension has not yet developed. Blood pressure should be monitored closely as it may appear later in the disease course 2.
Key Caveat
The 2022 study 5 examining ACOG guidelines in Bolivia found that ACOG criteria enable broader recognition of severe features beyond just eclampsia, but this study does not specifically address "atypical" HELLP criteria. The focus remains on recognizing the full spectrum of HELLP presentations, regardless of when hypertension appears.
In practice: Diagnose and treat HELLP syndrome based on the laboratory triad, regardless of hypertension timing. The term "atypical" is descriptive rather than a separate diagnostic entity requiring different criteria.