PIOPED

Quick Answer

PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis; JAMA 1990) was the multicenter study that defined the probabilistic language of the ventilation–perfusion (V/Q) scan for diagnosing pulmonary embolism. It showed that a high-probability scan makes PE likely and a normal perfusion scan effectively excludes it, but that most scans are non-diagnostic (low/intermediate probability) and must be combined with clinical pretest probability. PIOPED created the interpretive framework — high / intermediate / low / normal — that underlies V/Q reporting to this day.

The trial

Design: prospective, multicenter study (~931 patients analyzed) comparing V/Q scintigraphy against pulmonary angiography (the reference standard) in patients with suspected PE. It stratified scans by probability category and correlated each with angiographically proven PE and with prior clinical suspicion.

Key result

A high-probability scan had high specificity (PE present in the large majority) but limited sensitivity — many PEs occurred with non-high-probability scans. A normal/near-normal perfusion scan made PE very unlikely. Crucially, most scans were low or intermediate (non-diagnostic), and diagnostic accuracy improved markedly when scan probability was combined with clinical pretest probability (concordant high-probability scan + high clinical suspicion ≈ PE; concordant low-probability scan + low suspicion ≈ no PE).

Why it mattered

PIOPED standardized how V/Q scans are read and reported and cemented the principle that imaging must be interpreted with pretest probability — a foundational idea across diagnostic nuclear medicine. Its categories drove later refinements (revised PIOPED / PIOPED II criteria) and still frame modern V/Q and V/Q-SPECT interpretation, which remains valuable when CT pulmonary angiography is contraindicated (contrast allergy, renal impairment, pregnancy, radiation-dose concerns).

Context & caveats

PIOPED II (N Engl J Med 2006) later characterized CT pulmonary angiography, which became first-line in many settings; and PISAPED advanced a perfusion-only reading paradigm. V/Q retains a defined niche, and modern V/Q-SPECT with EANM criteria improves the non-diagnostic-rate problem PIOPED first quantified. The original study reference is verifiable on the JAMA Network article page.

Self-Check

Key References

• The PIOPED Investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism: results of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). JAMA 1990;263:2753–2759. JAMA Network article
• Stein PD, et al. Multidetector computed tomography for acute pulmonary embolism (PIOPED II). N Engl J Med 2006;354:2317–2327. doi:10.1056/NEJMoa052367