Tashikin

The Clear Pathway for the PU/PD Workup

Transform one of veterinary medicine's most complex challenges into a logical, step-by-step process designed for diagnostic confidence and efficiency.

From a Long List of Differentials to a Focused Plan

The differential diagnosis list for PU/PD is extensive, often leading to a costly and frustrating 'shotgun' approach. This protocol provides an engineered, three-tiered pathway to systematically and efficiently navigate the workup, preserving client resources and minimizing diagnostic friction.

1

The Foundational Database (Rule Out the Common Culprits)

  1. 1.1 Complete Urinalysis (UA)

    Action: Perform a complete urinalysis on a free-catch or cystocentesis sample, prioritizing a morning sample. Assess USG, dipstick chemistry, and sediment.

    Clinical Rationale

    The USG is the pivot point of the entire workup. A USG > 1.030 (canine) or > 1.035 (feline) makes significant PU/PD unlikely. The rest of the UA can immediately identify major rule-outs like diabetes mellitus (glucosuria) or evidence of pyelonephritis.

  2. 1.2 Comprehensive Serum Chemistry & CBC

    Action: Run a full serum chemistry panel, including electrolytes, and a complete blood count (CBC).

    Clinical Rationale

    This initial screen will identify the majority of common PU/PD causes, including chronic kidney disease (azotemia), diabetes mellitus (hyperglycemia), liver disease (low BUN, etc.), and hypercalcemia. The CBC can reveal evidence of infection or other systemic illness.

  3. 1.3 Total T4 (Geriatric Felines)

    Action: For any feline patient over 7 years of age presenting with PU/PD, a total T4 is a mandatory part of the initial database.

    Clinical Rationale

    Hyperthyroidism is a primary and common cause of PU/PD in older cats and must be ruled out early to avoid unnecessary further diagnostics.

2

Intermediate Investigation (For the Non-Obvious Case)

Entry Criteria: Proceed to this tier only if Tier 1 diagnostics are non-conclusive (i.e., no clear diagnosis of CKD, DM, Hyper-T, etc.) but the USG confirms inappropriately dilute urine.

  1. 2.1 Urine Culture & Sensitivity

    Action: Submit a cystocentesis urine sample for aerobic culture and sensitivity, regardless of sediment exam findings.

    Clinical Rationale

    Occult or 'silent' urinary tract infections, particularly pyelonephritis, can cause PU/PD. This is a critical and often overlooked rule-out before proceeding to more complex endocrine testing.

  2. 2.2 Urine Protein:Creatinine (UPC) Ratio

    Action: If proteinuria is noted on the initial dipstick, quantify it with a UPC ratio.

    Clinical Rationale

    Significant proteinuria can be an early indicator of glomerular disease that may not yet present with significant azotemia. This helps to further characterize potential renal causes.

3

Advanced Endocrine & Dynamic Testing

Entry Criteria: Proceed to this tier for persistent PU/PD after all causes in Tiers 1 & 2 have been definitively ruled out.

  1. 3.1 Hyperadrenocorticism (Cushing's) Testing

    Action: If Cushing's is suspected, perform an ACTH stimulation test using the Tashikin Cortisol Assay or a Low-Dose Dexamethasone Suppression Test (LDDST).

    Clinical Rationale

    Hyperadrenocorticism is a common cause of PU/PD in dogs. The choice between ACTH stim and LDDST depends on the clinical picture and index of suspicion. The ACTH stim is also the definitive test for iatrogenic Cushing's.

  2. 3.2 Modified Water Deprivation Test (WDT)

    Action: For cases where psychogenic polydipsia or central/nephrogenic diabetes insipidus (DI) is suspected. This test requires hospitalization and careful monitoring.

    Clinical Rationale

    The WDT is the final step to differentiate between the causes of profound polyuria with a consistently low USG. A positive response (urine concentration) rules out nephrogenic DI, with ADH response testing differentiating central DI from psychogenic polydipsia.