Your decision: three unknowns on the same shift

Three unrelated sediments cross the bench this shift. Unknown A is pH 5.8, specific gravity 1.020, with a few colorless bipyramidal envelope-shaped crystals; a same-day repeat on a re-mixed aliquot shows the same few forms, unchanged. Unknown B is pH 8.0, specific gravity 1.012, with several coffin-lid prism crystals and a few elongated prism forms in the same field, no reported symptoms supplied with the order. Unknown C is pH 5.2, specific gravity 1.015, with a small number of colorless hexagonal plate crystals, first seen on this specimen.

For each unknown, the task is the same one: read the chemical context, describe the full shape set present rather than the first shape that looks familiar, decide whether polarization would add anything, and decide whether specimen history changes the read. Then classify the finding as confident, probable, or requires review, and name one additional observation that would either confirm or overturn that classification.

Unknown A's pH and stable, unchanged shape across a same-day repeat support a defensible calcium oxalate dihydrate call at the confident-to-probable boundary; a polarization check adds little here because oxalate birefringence is inconsistent across sources. Unknown B's alkaline pH and coffin-lid shape support struvite, but the elongated prism forms in the same field overlap with calcium phosphate, so this is a probable call that benefits from comparison against the laboratory's reference atlas before it is finalized. Unknown C's hexagonal plate shape and acidic pH are compatible with cystine, and regardless of confidence in the shape call, this pattern routes to the laboratory's timely-review pathway because of what a confirmed cystinuria diagnosis requires beyond urine microscopy.

Confidence in a shape call and the need for review are two separate decisions; a crystal can be a confident morphology read and still require escalation.